strange acting T42 4L60E combo with 4wd tun file

[harascho]

Hi there,

I still have problems finding a suitable 4wd T42 TCM tun file for my 2007 LMG (E38)4L60E (T42) drive train.

Today I tried some different T42 .tun files. Now it is even more strange to me.
I have three different tun files. One 2wd (OS 24235341 cal 24234634)
and two 4wd (1st OS 24235341 cal 24233141 2nd OS 24239036 cal 24237445) ones.

One 2wd and one 4wd even have the same OS. I compared them with EFIlive and they are 100% the same. Isn't that strange?
The other 4wd ( 2007 Silverado) has a slightly newer OS.

First I corrected the speedo seetings ( now possible with the new EFIlive update) in all tun files and then I tried a full flash with the first 4wd file. No success, no part throttle shifts, no downshifts. Then I tried the second 4wd tun file with the newer OS.. full flash.. and the same as before, a strange acting tranny.
Last thing was going back to the 2wd tun file ( this is actual the one my T42 came with..) and with that tun file the tranny shifts as it should.

For me it seems, as soon as I load a 4wd tun file something goes wrong??
Could there be some mixed up wiring ?? I don't remember a TCM connection which has something to do with the transfercase ? The only signal is the 4wd low signal to the ECM and that is wired correct.

So far I can use the 2wd tun file, I have 2hi and 4hi but 4low doesn't work, the tranny doesn't shift at all, except when the rpm reaches the limit.

Any ideas?

Harald

[gmh308]

Hi there,

I still have problems finding a suitable 4wd T42 TCM tun file for my 2007 LMG (E38)4L60E (T42) drive train.

Today I tried some different T42 .tun files. Now it is even more strange to me.
I have three different tun files. One 2wd (OS 24235341 cal 24234634)
and two 4wd (1st OS 24235341 cal 24233141 2nd OS 24239036 cal 24237445) ones.

One 2wd and one 4wd even have the same OS. I compared them with EFIlive and they are 100% the same. Isn't that strange?
The other 4wd ( 2007 Silverado) has a slightly newer OS.

First I corrected the speedo seetings ( now possible with the new EFIlive update) in all tun files and then I tried a full flash with the first 4wd file. No success, no part throttle shifts, no downshifts. Then I tried the second 4wd tun file with the newer OS.. full flash.. and the same as before, a strange acting tranny.
Last thing was going back to the 2wd tun file ( this is actual the one my T42 came with..) and with that tun file the tranny shifts as it should.

For me it seems, as soon as I load a 4wd tun file something goes wrong??
Could there be some mixed up wiring ?? I don't remember a TCM connection which has something to do with the transfercase ? The only signal is the 4wd low signal to the ECM and that is wired correct.

So far I can use the 2wd tun file, I have 2hi and 4hi but 4low doesn't work, the tranny doesn't shift at all, except when the rpm reaches the limit.

Any ideas?

Harald

Dont know that this exactly helps, but the two T42 files with the same OS, if they have different segment part numbers, behavior/compatibility could be potentially quite different.

OS 24235341 cal 24234634 (+ diag & system)
OS 24235341 cal 24233141 (+ diag & system)

The T42 has cal, diag, and system segments + the OS. The only way two controllers are perfectly identical, is if the OS and segment PN's line up.

Even though the cals my appear identical in an EFILive comparison, if the PN's are different, there is a very good chance something is different in there.

I dont recall whether you were running a 2WD or 4WD OS in your ECM???

Cheers and have a good weekend!

[VEGASROBBI]

Hi Harold,

Funny how we are fighting the same issues so far apart.

I think this transfer case thing can be more complicated than you think; depending on what setup you have.

I have been trying to get my trasmission to shift in 4 Lo also.

My powertrain came out of a 07' Siverado 4x4 with the "Selectable" Transfer Case option and the "M" code LH6 engine. There is also a "Manual" Transfer Case offered which is significantly different in terms of wiring.

In my case the 4 Lo signal is sent to the Transfer Case Module from a Transfer Case feedback sensor, interpreted, then sent to the ECM and TCM via the "accessory wake up" data wire. I'm not sure exactly what this wire does but the Transfer Case Module not only shifts in and out of 4 wheel drive, Hi, Lo, etc. but also controls the front and rear axles.

So , I tried to hard wire the 4 Lo signal into the ECM as if it were the "Manual" Transfer case, no luck. Maybe my calibration won't recognize those terminals.

It will up shift in 4 Lo at about 3,500 RPM, too high. My feeling is the ECM thinks it is in 2 Hi and doesn't need to up shift at such a low vehicle speed. Even though the engine is revving up the ECM is not smart enough(or programed) to compare engine RPM vs. VSS. It needs a 4 Lo signal.

I'm going to try and install the VSS in the transfer case adaptor, i.e. on the output shaft of the transmission. This way the ECM will see the 2 Hi vehicle speed all the time. This should make the transmission shift normal in Hi and Lo. I'm sure this is not optimized as if the ECM and TCM knew they were in 4 Lo; but I'm hoping it will shift in Hi and Lo. Fortunatlly my truck has a speedo cable driven speedometer off the Transfer Case so the speedometer should read correct.

Not sure my dilema will help you but there it is thinking. If could get the 4 Lo and AFM working my conversion would be complete:)

Robbie

[VEGASROBBI]

BTW I don't have the original Tranfer case (axle on wrong side) or Tranfer case module. If you do then it seems to be a software issue. Make sure your truck is wired for the Transfer Case option you have and the calibration matches that.

Robbie

[gmh308]

In my case the 4 Lo signal is sent to the Transfer Case Module from a Transfer Case feedback sensor, interpreted, then sent to the ECM and TCM via the "accessory wake up" data wire. I'm not sure exactly what this wire does but the Transfer Case Module not only shifts in and out of 4 wheel drive, Hi, Lo, etc. but also controls the front and rear axles.

So , I tried to hard wire the 4 Lo signal into the ECM as if it were the "Manual" Transfer case, no luck. Maybe my calibration won't recognize those terminals.

Robbie

Not sure if it helps, but to clarify, the accessory wake up line is an accessory fed power feed to the ECM and TCM (etc).

It is there in most cases to support "wake up" of low speed serial data when the key is on accessory, vs ignition on/engine running.

Cheers.

[VEGASROBBI]

Then the data is sent from the Transfer Case Module via the serial bus and we are back to the AFM issue.

[harascho]

Ok here is my setup. new 2007 LMG engine, E38 with 4wd tun file and OS
4L60E (out of 4wd suburban) and T42 ( came from a 2wd application).

I still use the '97 transfer case the electric push button one not the autotrac 4x4
I think it is a NP 241

I got that 4wd low signal wired correct to the ECM ( and double checked.) So the ECM knows what to to with the transfer case tailshaft VSS when in 4wd low. So far all should be fine.
I will post my tun files tomorrow (have to copy them from the laptop..)
I also have to check if there is any wiring difference for a T42 in 2wd or 4wd applications, as for now I don't see a difference there..

Patrick gave me a hint to log the VSS signal as TCM and ECM see it in low and high range.
Robbie, it's really interesting having the same problems in NV and Germany.

Here's a link with some pics of my swap:

http://s301.photobucket.com/albums/nn67/harascho_album/?start=all

Harald

[harascho]

Hi folk,

I checked all the schematics, 2wd 4wd 4l60 E and transfercase (NP8 option)
So far I could not spot any wiring difference between 2wd and 4wd except that the ECM needs that 4wdlow signal to tell the ECM when the transfercase is in low range. That is exactly what is necessary for proper shifts in 4wdlow..

I have that signal but I have no shifts with a 4wd tun file in 2/4hi... Maybe I should load one again and check it in 4wdlow.. but that makes no sense 'cause it doesn't work in 2/4hi.

Here are the 2007 schematics, just in case...

[harascho]

the rest of the transfercase schematics

[VEGASROBBI]

http://www.chevyavalanchefanclub.com/cafcna/index.php?topic=41895.msg665705

Seems like we have conflicting information. According to Mitchell (not 100% trustworthy) there is no hard wire between the ECM, TCM and Transfer case module in the 2 speed automatic Transfer case.

Mitchell shows the LMG and LH6 having the exact same TC options. I can tell you my harness matches exactly to the selectable TC schematic and the only hard wire between the ECM and Transfer case module I see is the Accy wake up serial data wire. So, if that wire does not transfer data IM guessing it goes thru the computer data lines.

Only the manual TC shows the ECM getting the 4 Lo signal direct. I tried to wire my ECM this way with no luck; my VSS reads the same with signal or not.

For what it's worth here are the three diagrams I show for the LMG, I always trust factory diagrams over Mitchell, so if that is what you have take these with a grain of salt.

Robbie.

[harascho]

Only the manual TC shows the ECM getting the 4 Lo signal direct. I tried to wire my ECM this way with no luck; my VSS reads the same with signal or not.

You are correct Robbie, only the manual TC has that 4wdlow connection to the ECM. That is what I have to use, 'cause my old '97 TC and the TCCM has no other connections to the ECM.
Just to be sure I'll email you some schematics to compare with the Mitchel manual. ( I also have the Mitchel, an Alldata subscription for the '07 Suburban, and the GM manuals from '07..)

Harald

[harascho]

So , I tried to hard wire the 4 Lo signal into the ECM as if it were the "Manual" Transfer case, no luck. Maybe my calibration won't recognize those terminals.

I think this is something we should keep an eye on. If different ECM tun files have different settings for the ECM 4wdlow input then this is an explanation for our problems.
I remember Patrick (PSwired) saying that his combo (LMG plus 6 speed tranny) is shifting fine in 4wdlow but he also uses the 4wdlow input on the ECM and I have his original tun file in my ECM.. ?? even more questions...

Harald

[VEGASROBBI]

I went down the software path at first. Maybe a patch in the ECM to fool it into thinking it had a Manual TC and recognize the 4 lo input. But then what about the TCM calibration? Would it need to be modified? I like my tune and don't want to load a new one.

Since IM still fighting the AFM software issue already, I decided to go around the 4 lo problem.

I need a 40 tooth reluctor VSS anyway, so why not put it on the transmission output shaft and drive the speedometer from the TC.

I guess it's a hardware band aid for a software problem, hope it works.

These programmers are busy guys and will eventually get to all these issues , then it will become a matter of downloading software:)

[gmh308]

Hi guys, what was the original powertrain in these two trucks?

[harascho]

ok this is all to my best knowledge:

Parts summary 1997 Tahoe

Engine 5.3 LMG 1GKFC130X7R239150 2007 Yukon 5.3 2wd

ECM 3GNEC12047G152683 2007 Avalanche 2wd
12605897 YNAU service number 12597121 86ynauk16194d88a


Tranny 4L60E 1GNFK16367R390210 2007 Suburban 5.3 4wd

TCM 3GNEC12047G152683 2007 Suburban 2wd

Engine fuse box 1GNFK13087J142792 2007 Tahoe 5.3 4wd

BCM 1GKFK163X7R007000 2007 Yukon 4wd

Instrument cluster 1GNFK163X7J164217 2007 Suburban 4wd

Gas pedal 1GKFK13J67R003500 2007 Yukon 4wd

Air flow meter 1GCEC19C27Z500313 2007 Silverado 4.8 2wd


My Tahoe is/was 1997 2dr 4wd, engine 5.7 Vortec, tranny 4L60E, TC NP241 (which is the only 1997 part left in the drive train)

Harald

[gmh308]

ok this is all to my best knowledge:

Parts summary 1997 Tahoe

Engine 5.3 LMG 1GKFC130X7R239150 2007 Yukon 5.3 2wd

ECM 3GNEC12047G152683 2007 Avalanche 2wd
12605897 YNAU service number 12597121 86ynauk16194d88a


Tranny 4L60E 1GNFK16367R390210 2007 Suburban 5.3 4wd

TCM 3GNEC12047G152683 2007 Suburban 2wd

Engine fuse box 1GNFK13087J142792 2007 Tahoe 5.3 4wd

BCM 1GKFK163X7R007000 2007 Yukon 4wd

Instrument cluster 1GNFK163X7J164217 2007 Suburban 4wd

Gas pedal 1GKFK13J67R003500 2007 Yukon 4wd

Air flow meter 1GCEC19C27Z500313 2007 Silverado 4.8 2wd


My Tahoe is/was 1997 2dr 4wd, engine 5.7 Vortec, tranny 4L60E, TC NP241 (which is the only 1997 part left in the drive train)

Harald

Ok good. Do you have the correct VIN's these items are out of? Some of the VIN's have been zeroed which makes them difficult to check.

And are you using the BCM?

Cheers.

[PSWired]

To provide some more information, here's my setup:

2009 5.3 LMG engine from 4WD tahoe (unknown transfer case type, but can dig up the VIN if you guys want)
2007 6L80e transmission, 4WD version
NP241 transfer case
1995 GMC Yukon 4WD

The VSS signal comes from the 6L80e internal sensors. The transfer case output shaft mounted VSS is used only for the ABS system and my speedometer (temporarily until I get the CAN interface box built). The 4LO signal from the transfer case goes to the ECM pin per the GM diagrams.

The transmission shifts normally in 4LO. However, the speed as seen by the ECM is incorrect when in 4LO mode. I am going to wait until I have the matching 2009 OS and cal in the TCM before I do any further troubleshooting. There are some little incompatibilities between the '07 and '09 operating systems. Waiting on 2009 T43 support from EFILive before doing anything else.

[harascho]

@ Patrick: Wasn't that a 2007 5.3 LMG with an ECM and 2009 OS or am I confused 'cause it's too cold over here?
And just to be very sure, I think I asked before, that 4wdlow signal to the ECM is a low active signal (low when in 4wdlow)

@gm308: Those VIN infos is all I got. Yes I use the BCM. I wired all my exterior lights in the 2007 way with the BCM as the "master". I also got the auto headlight running thanks to an ambient light sensor. The last thing I wired is the RCDLR to get the tire pressure monitor system runnig. As soon as I have new valve stems I will mount the sensors.

Harald

[gmh308]

@ Patrick: Wasn't that a 2007 5.3 LMG with an ECM and 2009 OS or am I confused 'cause it's too cold over here?
And just to be very sure, I think I asked before, that 4wdlow signal to the ECM is a low active signal (low when in 4wdlow)

@gm308: Those VIN infos is all I got. Yes I use the BCM. I wired all my exterior lights in the 2007 way with the BCM as the "master". I also got the auto headlight running thanks to an ambient light sensor. The last thing I wired is the RCDLR to get the tire pressure monitor system runnig. As soon as I have new valve stems I will mount the sensors.

Harald

That is a real mix of different parts.

Are you 100% sure your ECM and TCM and BCM are a matched set for 4WD?

:)

[harascho]

No I'm not.

TCM, ECM and engine came from 2wd applications only the BCM and tranny were 4wd.

I thought that there is no hardware difference in the components (ECM, TCM..) between 2wd and 4wd this is just a matter of the OS and calibration?

I have Patricks OS and calibration in my ECM (his ECM was 4wd..and had the same OS..) and now I am fighting with the TCM 4wd tunes...

The more I dig into it the more confusion is in my head....

Harald

[harascho]

I made some runs this afternoon.....

The speed is ok in low range...didn't expect anything else with the VSS in the transfercase tailhousing.

The shifts appear at about 3500rpm... when I revved it to about 2800 - 3000rpm and lifted the throttle a bit the tranny shifted.
I attach a log file but as I did my first data logging today don't expect miracles from it...

Harald

[VEGASROBBI]

Here is my info;

VIN 2GCEK13M071547739, 5.3 LH6 from a 2007 Silverado.
E38 ECM OS 12614088, Calibration 12614085
4l65E Transmission
T42 TCM OS 24239036, Calibration 24237445
I am not running a BCM.

The engine, transmission, TCM, and ECM are all from the same vehicle which was a 4WD. IM using the original wiring harness from the same vehicle.
My Transfer Case is a NP208 from an early Blazer.

Harold, I think that is the point. Your VSS will always read correctly while in the TC; but, until the ECM/TCM knows it is in 4 lo, they will try and shift as if they are in high range.

I see no 4 lo shift table available. In my tune under "Drivetrain" 4WD is selected. Then the 4 lo ratio is specified, say 2:1. EFI Live reads "4WD Low gear ratio, used to adjust the transmission output speed ratio when in 4WD Low."

So IM guessing in 4 lo the TOS is used to calculate shift points, not the VSS.

Robbie

[PSWired]

@ Patrick: Wasn't that a 2007 5.3 LMG with an ECM and 2009 OS or am I confused 'cause it's too cold over here?
And just to be very sure, I think I asked before, that 4wdlow signal to the ECM is a low active signal (low when in 4wdlow)

Harald

Yes, the engine hardware is 2007 model year, the ECM is just loaded with a 2009 OS and calibration.

[harascho]

Robbie, that's exactly what my tun says:

see:



Harald

[gmh308]

No I'm not.

TCM, ECM and engine came from 2wd applications only the BCM and tranny were 4wd.

I thought that there is no hardware difference in the components (ECM, TCM..) between 2wd and 4wd this is just a matter of the OS and calibration?

I have Patricks OS and calibration in my ECM (his ECM was 4wd..and had the same OS..) and now I am fighting with the TCM 4wd tunes...

The more I dig into it the more confusion is in my head....

Harald

Yes this is a confusing situation, but i think you will need the ECM and TCM to match the BCM based on a VIN.

:cheers:

[harascho]

I must agree. So I planned a visit to a German Opel/GM Dealer to get the latest updates for my ECM / TCM and BCM.

I looked up for a suitable 2007 Tahoe on ebay motors ( same configuration of engine , tranny and 4wd)
Took this VIN and ran it in TIS. I think this way I will get some matching OS and calibrations for ECM, TCM and BCM.
I also looked into 2008 Tahoes, but I think I will better choose the 2007 system.

In a few hours I will know more...

Harald

[harascho]

As I wrote in my last post I went to a GM dealer to get all the TIS updates which were avaiable for that 2007 Tahoe I have choosen as a base line. (Same engine /tranny combo as mine..).

All went fine, and now I have matching OS and calibrations in ECM, TCM and BCM.

The first testdrive was interesting. Again that strange acting not shifting tranny in 2hi. No part throttle shifts no TCC lockup. Then I tried 4wdlo and that was even more interesting, 'cause the tranny was shifting quite normal. For me it seems the speedo was only half of the real speed in 4lo but I could be wrong with this.

For me it's obvious that I might have mixed up the 4wdlo signal to the ECM. I think I wired it as a low active signal (low when in 4wdlo) but I guess it's worth a trial wiring the 4wdlo signal as a high active signal.

Harald

[VEGASROBBI]

Harald, does sending the 4 low signal have any effect on the ECM?

I recieved my new Transmission Output Shaft VSS today, I will it install it this weekend.

Harald I uploaded some pics of my project for you, check them out.

http://s418.photobucket.com/albums/pp265/VEGASROBBI/

[gmh308]

Harald, does sending the 4 low signal have any effect on the ECM?

I recieved my new Transmission Output Shaft VSS today, I will it install it this weekend.

Harald I uploaded some pics of my project for you, check them out.

http://s418.photobucket.com/albums/pp265/VEGASROBBI/

One of the purposes of the 4WD Lo input to the ECM is to change the speed limiting number.

[harascho]

Hi there,

I had some time for a few trials. Fresh from the GM dealer I have a matching set of 2007 4wd Tahoe 5.3 LMG 4L60E files in ECM, TCM and BCM.

4wdlo works, tranny shifts nice. 2hi doesn't work no part throttle shifts no downshifts, I only realize one shift at all.

Ok I built a harness where I could change the logic of the 4wdlo signal which goes to C1 pin 2 of the E38 ECM. I now can change the 4wdlo signal to active high (12V) or active low (GND). I also checked the ECM tune for correct tire size, gear ratios and 4wd type. Then I set the speed limiter to 170km/h and the low range speed limit to 70km/h. The T42 tune file has the same tire size settings. After flashing both controllers, the first testdrive was a disapointment: 2hi not working, 4lo working, no matter what logic setting I use for the 4wdlo signal. I went back to a 2wd tune (my t42 came with this one) And did a second check... funny I ended with the speed limiter cutting in in 2 hi at 70km/h and guess what, it did so no matter what logic setting I used for the 4wdlo signal.

Next test.. I did a full flash of the T42 with the tune file of the matching set I described above and checked that:

Transfer Case Ratio TCRATIO :1 Transmission 2 GM.TCRATIO PID

but no matter to which controller I connected that PID gave me strange values. If I look into the ECM that value is 8.00 : 1 and If I look into the TCM I see 2,65:1 and that doesn' change with 2hi or 4lo at all....

any ideas are very very welcome....

Harald

[VEGASROBBI]

Well as usual it was not as easy as it could have been. The reluctor did not fit my output shaft, so I had to machine the adaptor and make a split collar to fit the shaft since the output splines were a larger diameter than the shaft where the reluctor mounted.

I now have a strong 40 pulse 12v AC sine wave:).

My transmission now shifts well in both 4lo and 4 hi.

Of coarse the vss reads incorrectly when in 4 lo but so far it has not thrown any codes; and drivability seems fine in 4 lo. This will have to do till the rocket scientists decode the software.

I guess my built in speed limiter(right foot) will have to suffice.

[VEGASROBBI]

Harlod,

I feel your pain. A couple questions;

When you had your modules flashed; was it with the "manual" TC calibration?

Do you notice any pid change when you switch the 4 lo input from hi to lo? ECM, TCM or BCM?

I guess what IM getting at is; is pin C1-2 active or is the ECM looking for the dreaded serial data? I tried every parameter with different inputs to pin C1-2 with no results.

Can you activate pin C1-2 with the 4WD parameter in EFI Live, or is it a different OS than the automatic TC's?

Seems like your ECM is treating 4 lo as 4 hi?

IM hoping some knowledgable programmers can help?

[VEGASROBBI]

OK, after being in 4WD lo for a while it threw a code 2771, "4 Lo Input Signal". I cycled the key now it is in history and CEL out..

4 lo and hi still work fine. Running this code may help.

[harascho]

yes, it seems my ECM sees no difference between 2hi, 4hi and 4lo and even worse, it seems that the ECM is thinking we are in 4lo all the time. That would explain the correct shifting in 4lo, the not so correct shifting in 2hi and the speed limiter cutting in in 2hi at the desired speed limiting setting for 4 lo.

( I didn't realize that earlier, 'cause no extra 4lo speed limit was set.. hmm maybe that also explains my bad mileage in 2hi, maybe some parameters are different in 4lo ??.. Strange is also with a 2wd tune in the TCM and no speed limits set for 4lo in the ECM I have quite nice shifts..? huuuuhhhhh)

All together I see a bad thing comming towards me: I had to wire that ECM C1,2 PIN by myself, so just in case something went wrong with that PIN when I first connected the C1 ( maybe a bent pin??) then the signal 4lo, which I checked several times at the connector, doesn't reach the ECM itsself..?????

I will look at the ECM's PIN's later the day....

By the way great pics, Robbie.... snow so close to Vegas,, that's a very rare occasion. Also your swap pics look good, great welding on the exhaust parts..

Harald

[harascho]

ohhhh I was goofin' around with some of the Speedo parameters.
I had the speed limiter H0129 at 170km/h and the low range limiter H0155 to 70km/h. The speed limiter source H0156 was ECM and in other tests "other module".
Then I had the possibility to play with the ECM's C1,2 (4wdlo) input. I could set this to active high logic and active low logic.

What I can say is the following: once I had a setting where I had good shifts in 4wdlo, changed the logic of the 4wdlo signal and that resulted in good shifts in 2hi. In both!! cases the speed limit in H0155 was cutting in in 2hi.

I then raised the H0155 to the same as H0129 and I guessed to have a good low range or a good 2hi depending on the choosen logic of C1,2... No,... that was not the case... Goofing around with the speed limiter in 4wdlo (H0155) showed me that a set H0155 cuts in in 2hi, no matter what the input C1,2 is set to. A few more tests showed, that I wasn't able to get good shifts in 2hi again.
I guess (hope..) there is something wrong in the area 4wdlo input of the ECM (and its logic..) speed limiter H0155 and maybe the speed limiter source. Sadly I wasn't able to produce any conclusive results maybe some other things are also a player in this "game".

here are my tun files... just in case.. EFI live is latest built 78

Last question:

if H0159 is activated, can I adjust that output with H0105 and is H0105 only acting on the ECM's VSS output ( I think pin 57..) and not on all the other VSS values on the GMLAN?

I know.. lots of questions.... I know....

Harald

[VEGASROBBI]

I could not find P2771 in Mitchell so take a look at this.

P2771 is '4wd low switch circuit'

Circuit Description with 4L60-E / 4L65-E Automatic Transmission
For vehicles equipped with an active transfer case, the four wheel drive (4WD) low circuit consists of the powertrain control module (PCM) , a transfer case control module and the circuit wiring. The transfer case control module controls the 4WD low signal on the low signal circuit. When the operator selects 4WD low, the transfer case control module grounds the signal circuit, and the 4WD low signal voltage on the circuit changes from ignition voltage to zero volts. The PCM then compensates for transfer case gear reduction in the transmission output shaft speed (OSS) sensor signal. The PCM uses the transmission OSS sensor signal to adjust shift points, line pressure and torque converter clutch (TCC) scheduling.

For vehicles not equipped with an active transfer case, the 4WD low circuit consists of the PCM, a transfer case switch and the circuit wiring. The transfer case switch controls the 4WD low signal on the signal circuit. When the operator selects 4WD low, the transfer case switch closes and the 4WD low signal voltage on the signal circuit changes from ignition voltage to zero volts. The PCM then compensates for transfer case gear reduction in the transmission output shaft speed (OSS) sensor signal. The PCM uses the transmission OSS sensor signal to adjust shift points, line pressure and TCC scheduling.

When the PCM detects a continuous open, short to ground or short to voltage in the 4WD low circuit, then DTC P2771 sets. DTC P2771 is a type B DTC.

DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P2771 Four Wheel Drive (4WD) Low Switch Circuit

Conditions for Running the DTC

No TP sensor DTCs P0122, or P0123.
No VSS DTCs P0502 or P0503.
No TCC solenoid valve DTC P0740.
No TCC stuck ON DTC P0742.
No 1-2 SS valve DTCs P0751 or P0753.
No 2-3 SS valve DTCs P0756 or P0758.
No TFP manual valve position switch DTC P1810.
No TCC PWM solenoid valve DTC P2761.
The engine speed is greater than 450 RPM for 5 seconds.
The engine is not in fuel cutoff.
The vehicle speed is greater than 11 km/h (7 mph) .
The TP angle is 17-50 percent.
The engine torque is 54 - 542 Nm (40 - 400 ft. lbs.) .
The engine vacuum is 0-105 kPa (0-15 psi) .
The gear range is D4.
The shift solenoid performance counters are zero.
The TFT is 20-130°C (68-266°F) .
Conditions for Setting the DTC
DTC P2771 sets if one of the following conditions occurs:

Condition 1



The 4WD low switch is in 4WD low.
The transfer case is not in 4WD low.
The TCC slip speed is -3,000 to -50 RPM.
The transfer case ratio is 0.08-1.2, the transfer case ratio is the engine speed divided by the transfer case output speed.
All conditions are met for 5 seconds.
Condition 2



The 4WD low switch is not in 4WD low.
The transfer case is in 4WD low.
The TCC is commanded ON.
The TCC slip speed is 100 to 3,000 RPM.
The transfer case ratio is 2.5-2.9.
All conditions are met for 10 seconds.
Action Taken When the DTC Sets



The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
The PCM commands a normal shift pattern, not a 4WD low shift pattern.
The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
The PCM stores DTC P2771 in PCM history during the second consecutive trip in which the Conditions for Setting the DTC are met.
Conditions for Clearing the MIL/DTC



The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
A scan tool can clear the MIL/DTC.
The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
The PCM cancels the DTC default actions when the fault no longer exists and/or the ignition switch is OFF long enough in order to power down the PCM.



So... it seems that if the switch set to 4wd low and the t case is not in 4wd low, or vise versa you will get the code... seems like it could be the encoder?

[harascho]

That's a brief description.

Now we have +12V at C1,2 in 2hi, 4hi and GND in 4Lo so that is answered. Or in other words we have an open circuit in 2hi/4hi and C1,2 is grounded in 4wdlo.

I think I know what is wrong with my circiut. I use the NP246 4wdlo switches control bulb as my signal source. It is GND when the bulb is switched on... (transfer case in 4wdlo) but it doesn't reach IGN Voltage cause the bulb itsself is in series, I only read 10,3 V. ( the C1,2 input has a internal pullup resistor to 12V so that Voltage drop of 1,7V seems to confuse the things.)

If I take this in consideration it could explain that my tranny always thinks that the transfercase in in 4wdlow.

I will check this tomorrow..

Good work Robbi

[harascho]

Ok... the signal polarity of 4wdlo is clear and I corrected my circiut according to that. The open ECM pin C1,2 has IGN voltage through an internal pullup resistor. When the TC is in 4lo that circuit is grounded.

Now the strange things begin: The 4L60E shifts normal in 4lo and a bit strange in 2hi. I cannot get any downshifts when I press the pedal to the metal...
I then tried the 4wdlo speed limiter with both settings of the source "ECM" or "other source" and it didn't kick in , nor in 4lo, neither in 2hi as the days before.

I don't know if I make mistakes or if there is a bug somewhere in the area 4wdlo signal, speed limiters in 2hi 4 lo and the ratio settings for the transfer case.
My problem is I am not able to produce any conclusive results cause the behavoiur is always different.

I checked the factory setting of that tune file ('07 Tahoe 1GNFK13037R238413) and saw that the speed limiting source was "other" and that the limits for 4lo and 2hi were the same. I also checked the 4wd option of that Tahoe, it's NP8 which says that the ECM C1,2 should work as 4wdlo input PIN.

I then compared that Tahoes TCM tune file with the 2wd tune file I have as the only one which lets my tranny shift as it should. From a first comparison I cannot see any differences in the settings.

Please can someone bring some light in this dark TCM , ECM tuning ....

Harald

[VEGASROBBI]

There are two orange/black wires from the ECM, pin 1 and 71 that say "replicated TOS signal". One goes to the TCM, the other to the Transmission Range Switch; are they in place?

[harascho]

Isn't that the P/N switch signal??? .. I will check this afternoon.

here is what I have:

Summary:

2hi ok -- 2wd tun in TCM -- 4lo not ok

2hi not ok -- 4wd tun in TCM -- 4lo ok



Conversion:

'97 NP241 electric shift TC. VSS in TC tailshaft. This VSS signal wired to the VSS inputs of the TCM.


Important:

parallel to the TCM's VSS inputs is a '95 VSSB to get the necessary signals for the '97 antilock

(128.000 pulses/mile) . The signals look ok.


speed limit 4lo:

intermittent works on 4lo and 2hi
intermittent doesn't work on 4lo and 2hi this happens without changing anything

Facts:

4wdlo input ECM C1,2 PIN is grounded when in 4lo, circiut checked and ok

guesswork:

1st guess: The OS (2007 Tahoe with NP8 option) isn't reading the C1,2
2nd guess: the VSSB parallel to the TCM's VSS inputs confuses things.. sometimes.. which could

explain those non conclusive results I have when testing.

help:

how can I check/activate the 4wdlo C1,2 input on the E38. My OS and tune support option NP8 which indeed should activate that pin.

Can I programm the E38 VSS output to get my '97 antilock working with it.?

Harald

[gmh308]

This wont help, but it will give an insight into how much may still be sitting in the background:

http://forum.efilive.com/showthread.php?t=9761&goto=newpost

E38 C1 Pin 1 is the P/N safety start signal. Pin 71 as VRobbie mentions is the speed sensor repeat line. The TOSS feeds into the T42 which repeats it and sends it on into the E38.

It looks like you are trying to mix '95 and '97 subsystems with '07 controllers. IMHO: If the systems arent compatible, it would be pure luck that would enable them to work.

Does '97 ABS expect a raw TOSS or speedo signal? Or VSS via CAN?


Isn't that the P/N switch signal??? .. I will check this afternoon.

here is what I have:

Summary:

2hi ok -- 2wd tun in TCM -- 4lo not ok

2hi not ok -- 4wd tun in TCM -- 4lo ok



Conversion:

'97 NP241 electric shift TC. VSS in TC tailshaft. This VSS signal wired to the VSS inputs of the TCM.


Important:

parallel to the TCM's VSS inputs is a '95 VSSB to get the necessary signals for the '97 antilock

(128.000 pulses/mile) . The signals look ok.


speed limit 4lo:

intermittent works on 4lo and 2hi
intermittent doesn't work on 4lo and 2hi this happens without changing anything

Facts:

4wdlo input ECM C1,2 PIN is grounded when in 4lo, circiut checked and ok

guesswork:

1st guess: The OS (2007 Tahoe with NP8 option) isn't reading the C1,2
2nd guess: the VSSB parallel to the TCM's VSS inputs confuses things.. sometimes.. which could

explain those non conclusive results I have when testing.

help:

how can I check/activate the 4wdlo C1,2 input on the E38. My OS and tune support option NP8 which indeed should activate that pin.

Can I programm the E38 VSS output to get my '97 antilock working with it.?

Harald

[harascho]

Hi,


E38 C1 Pin 1 is the P/N safety start signal. Pin 71 as VRobbie mentions is the speed sensor repeat line. The TOSS feeds into the T42 which repeats it and sends it on into the E38.

It looks like you are trying to mix '95 and '97 subsystems with '07 controllers. IMHO: If the systems arent compatible, it would be pure luck that would enable them to work.

Does '97 ABS expect a raw TOSS or speedo signal? Or VSS via CAN?

'97 ABS expects 128.000 pulses/mile speedo signal on it's VSS input PIN
I use that '95 VSSB to built the signal out of the '97 TC tailshaft VSS sensor. (from the VSS sensors sine wave to the square wave with the correct resolution in respect of tire size and axle ratio)

It works, but it seems to disturb the VSS signal to the TCM .. at least somtimes I am not sure, cause the signals look good.

That thread is interesting, but on my side as I have a E38 /T42/BCM combination with the correct drivetrain OS and tunes, and my schematics say C1,2 is for option NP8 TC then I should be fine. C1,2 isn't doing what it shoud do. Could be a glitch in my schematics (GM manual..) or it could be that we have a software bug somewhere that the 4wdlo input on the E38 isn't activated although it should be according to OS and tun file.

A PID which shows the TC state would be nice but that TC state I found reads incorrect, from 8.00:1 when looked into the E38 to 2,65:1 when looked into the T42, and it doesn't change at all when I ground E38 pin C1,2.

So there is definetly something wrong... maybe a thing for Paul and Ross to take a look at??

Harald

[waynehartwig]

Dredging this back up from the dead.

I just put an 08 Sierra 4x4 5.3/4L60E into my 04 Jeep Wrangler and I'm having the same weird shifting issues - no wot/partial shifts. Well, not always. In 3500 miles, it has shifted correctly on it's own 4-5 times. No matter what I set my shift points to (in any of th etables), it won't follow them.

Sounds like I need to put a 2wd ECM/TCM OS in my rig?

[ScarabEpic22]

All ECM/TCMs are the same, just have to flash them with the proper OS to make it work. Since you're swap is custom, just make sure you use files with the same OS (and preferably same year too). Maybe get 08 Sierra 2wd 5.3/4L60E files and flash that.

[waynehartwig]

All ECM/TCMs are the same, just have to flash them with the proper OS to make it work. Since you're swap is custom, just make sure you use files with the same OS (and preferably same year too). Maybe get 08 Sierra 2wd 5.3/4L60E files and flash that.

The problem is there was apparently never a 2wd version of my donor - I've been playing with that over the past week, before I even saw this thread. I went through the trouble of making a new VIN and the new VIN shows invalid on the TIS website. 1GTEK19J58Z is the correct VIN and 1GTEC19J98Z is my made up VIN. It's a correct VIN as far as VIN's go, just not according to GM.

However, I found a Silverado :D 1GCEC19J28Z :rockon: If you know how to read VIN's, you'll notice the only difference is the make (model isn't in the VIN), 2x4 and check digit. :grin:

I've already compared his stock tune with mine and they are the same, but when you look at the segment/file numbers, some are different. Both are the same OS.

...I think I'll go change my VIN to match his, then apply his tune and see what happens. Worst case I use up some credits, right? Best case it works and I'm still able to use my Edge controller. :cheers:

[joecar]

You will use up a credit only if you flash a different PCM/ECM/TCM...

i.e. you can flash different file/os/vin for free.

[harascho]

Hi waynehartwig,

just read here : http://forum.efilive.com/showthread.php?t=9960&page=2

and see what we did. Summary is for a correct setup with 4wd tunes in T42 and E38 you need the TCCM of a TC of the year your components are.

I am running 2wd tunes in E38 and T42 right now with the drawback of a not shifting tranny in 4wdlow. This will be addressed soon. I will use a 2007 NP8 option TCCM to control my '97 Tahoes TC (NP243). This will involve some electric workarounds but I think I will be able to get it running, without auto 4x4 that's clear.

Harald

[waynehartwig]

You will use up a credit only if you flash a different PCM/ECM/TCM...

i.e. you can flash different file/os/vin for free.

I don't believe the other guys work this way, as I don't have EFILive. :doh2: I believe with them I have to license the file and then relicense the ECM with the new VIN. But we'll see. If this fixes it, I'm more than happy to pay for this. At this point I just want it fixed. The drag strip is open and I'm itchin' to go play!

[waynehartwig]

Hi waynehartwig,

just read here : http://forum.efilive.com/showthread.php?t=9960&page=2

and see what we did. Summary is for a correct setup with 4wd tunes in T42 and E38 you need the TCCM of a TC of the year your components are.

I am running 2wd tunes in E38 and T42 right now with the drawback of a not shifting tranny in 4wdlow. This will be addressed soon. I will use a 2007 NP8 option TCCM to control my '97 Tahoes TC (NP243). This will involve some electric workarounds but I think I will be able to get it running, without auto 4x4 that's clear.

Harald

I don't have access to the TCCM or TC from the donor rig. I also am running an Atlas transfer case, fully manual. So if I don't need to add all of this extra stuff or downgrade TC's, I'd be happier.

[waynehartwig]

Hi waynehartwig,

just read here : http://forum.efilive.com/showthread.php?t=9960&page=2

and see what we did. Summary is for a correct setup with 4wd tunes in T42 and E38 you need the TCCM of a TC of the year your components are.

I am running 2wd tunes in E38 and T42 right now with the drawback of a not shifting tranny in 4wdlow. This will be addressed soon. I will use a 2007 NP8 option TCCM to control my '97 Tahoes TC (NP243). This will involve some electric workarounds but I think I will be able to get it running, without auto 4x4 that's clear.

Harald

As I mentioned in the other thread, I have my VSS on the output shaft of the trans and mine shifts the same, regardless of where the TC is. So maybe this and a 2wd tune is what you guys need? And a manual transfer case of course :D

[ScarabEpic22]

See you're in Mead, Im in Spokane right now man. If you need someone with EFILive to test this with, hit me up and if you pay for the VIN license (99 bucks) Id be happy to help you out with this. Got finals tomorrow and friday, but if you want to meet up for an hour or so on saturday before I head back to Seattle Id be more than happy to.

[waynehartwig]

See you're in Mead, Im in Spokane right now man. If you need someone with EFILive to test this with, hit me up and if you pay for the VIN license (99 bucks) Id be happy to help you out with this. Got finals tomorrow and friday, but if you want to meet up for an hour or so on saturday before I head back to Seattle Id be more than happy to.

Already got it fixed, but thanks! I basically just put an 08 Silverado 2x4 tune into the ECM/TCM and that solved my shifting issues. :rockon:

[GAMEOVER]

Good info in this thread...
Ooops didn't realize it was so old...:shock: