4L85E TCC Tuning Help

[jlane330]

I've been reading everything I can on here and can't seem to find an answer to some of my questions. A little background:

2006 Duramax Van with 4L85E Transmission
Mild (~40HP) engine tune, Estimate 600 ft lb
75K miles total

Has been running well the last 5 years until last week, when I got a P0894 (Slipping transmission components) code out of the blue. Did not notice ANY slipping issues, cleared the code, and it's reappeared. I dropped the pan, changed the filter and TCC PWM solenoid (just in case), and added new fluid. Old fluid looked excellent when drained, inside of pan was VERY clean, etc. No obvious issues inside. I can drive it around town and no code appears. Hit the freeway and the code pops up while cruising (does not require heavy throttle to cause the MIL). Again, no signs of slipping that I notice (do not have a Tach or Temp Gauge for transmission). I feel like it's related to the TCC as I can be cruising in 4th gear and stomp on the skinny pedal and it moves out very well (no obvious signs of slipping at all). I can't tell if the TCC is locking though or staying locked.

I saved the Freeze Frames that were generated with the DTC. They are .txt files, and in binary format. How do I open these so I can see the parameters present when the DTC was set? The ECM FF are readable, but not the TCM FF.

I see the TCC area of the tune and am a little lost on what to try. I've read a lot about changing the TCC lock-up from PWM to On/Off. Is it as easy as changing {D6031} TCC Solenoid Minimum PWM to be 100 everywhere? It appears that the Maximum PWM table is already set to 100 everywhere.

Recommendations on what to set the TCC Apply Rate to? What are the units for this table? Stock table numbers are between 0 and 12.

Recommendations for {D6035} TCC Apply/Release Max Pressure? Looks like this ramps up as engine torque increases (makes sense), and seems like increasing these values on the lower end of the torque axis and smoothing would mean that the TCC would apply more firmly, perhaps reducing or eliminating TCC slip. Does this sound correct?

How do I change the table scales for Engine Torque? The tables currently go up to 472 Ft-Lbs. What happens if the engine is delivering 550 FT-Lbs, for example? Are the 472 FT-Lbs values used when the engine torque exceeds the table size, or could this be the root cause of the issues? I can't find a place to change this scale but would like to expand the tables to 600 FT-lbs if possible.

I would really appreciate any and all help you guys can provide. I don't feel like the transmission is in need of a rebuild (maybe it does, but my gut tells me something else might be up). I want to make sure that the issue isn't the tune before plunking down money for a new torque converter and tranny. Side note, I've read about others with these vans have issues like this too. They kept replacing torque converters and transmissions and still had issues. I'm not looking for hard core street rod shifting, but can easily deal with firmer shifts than stock (it's pretty soft feeling).

Thank you very much!
Joshua

[ScarabEpic22]

Hey Josh, would you mind posting your TCM tune so we can take a look?

On gassers, I much prefer the "on/off" style lockup on vehicles that can handle it, set the Min TCC PWM table to like 95 or 98 across the board. This can be hard on the lockup clutch, so use with caution.

Engine TQ, if the signal value is greater than the last column value, it will simply use the last programmed value.

[joecar]

Also check if the are any other DTC's...?

[jlane330]

Erik and Joe,

Thanks for the responses. I did some more digging on my issue and here's the progress:

1. Other DTCs. Yes, I had three total DTCs. One was from the TCM (P0894). Another was from the ECM simply stating that the TCM requested the SES light on. Finally, the third was one that I've been battling for the last 5+ years...EGR insufficient flow. In spite of trying various changes in my tune I can't get this to not come up. Of course there is a EGR blocker installed. No other codes present. Would love to solve the EGR code issue one day...

2. I would like to share the TCM tune. What's the best way to attach that file here?

3. I figured out how to datalog and recorded several logs with many of the TCM TCC related PIDs selected. I cleared the codes and started datalogging and driving until I got issues. Good news is that the transmission temp looks reasonable. It hit 196 deg F maximum driving for approx. half an hour down the freeway (75ish mph). This explains why the fluid still looks ok. I don't think I cooked the fluid or tranny with heat...yet. Again, how would I share these datalog files?

4. Of course the SES light came on after a while.

Here's a screenshot of a peculiar (IMO) spot in the datalog. I'd guess this is about the time that I got the SES light on. BTW, can I datalog exactly when the DTC is set? If so, how?
20150
20151

Based on what I see, I was cruising down the freeway (speed constant at 71 mph, rpm constant around 2100 rpm, in 4th gear). Around frame 15350 it appears that the TCC is commanded not to enable (based on the TCCC PID). The RPM remains quite constant whether TCC is ON of OFF. It appears that TCC ON made no difference to the TCCSLIP rpm. Not sure how the TCCP pressure is measured, but when commanded ON, it appears that there is pressure, and when OFF, no pressure is recorded.

My understanding is that slippage could be the result of either the TCC not locking, or 4th gear not holding. TCCSERR seems to indicate that it's the TCC not locking, but not sure how reliable that is. I would assume that if it was 4th gear clutches not holding, that it'd have more TCCSLIP as engine torque increased. What I notice in the datalog is that the TCCSLIP decreased as the RPM and engine power increased. Maybe it's the converter approaching stall speed, so the slip decreases? Anyway, how do I separate these and decide is the trans needs a build or if the converter is the issue? Or, any other ideas on what could be wrong?

Thank you in advance for any and all help!
Joshua

[ScarabEpic22]

Click "Go Advanced" at the bottom of the quick reply box, then you should be able to see an attachments icon (next to emojii and fonts). Tune and datalogs can be added this way.

It looks like in one screenshot the slip error is rising and matching the pressure (I'd expect that, adding pressure to try and control slip), but slip keeps rising. I wonder if you're hitting a slip limit? (I know the Allisons have this, not sure about the 4LxxE family.) TCMPSLIP looks like it's going crazy, but I dont know it that's normal or not as I've never logged it. At the beginning and end of the log, there is significantly more slip occuring TCCSLIP and it looks like it never gets to 0 RPM of slip. Usually a few RPM isnt a big deal, but that looks pretty significant across the board (maybe zoom in and see what the actual slip values are).

[jlane330]

Thanks for the tip on attaching the tune/datalogs. I'll attach them when I get home this evening.

I haven't noticed any slip limit parameters in the tune to set. The only slip limit I know of is in regard to setting the P0894 code. I forget the actual numbers, (-20 to 40 rpm IIRC) but if a slip is detected for a period of time, then it will throw the code. I'd have to look this up again in the FSM for the exact conditions. I have followed some of the diagnostic tests in the FSM. One test that needs to be done is to drive in 3rd and force the TCC lock-up. Apparently this test will tell if it's the TCC or the clutch pack slipping. MY hunch is that it's the TCC, but want to confirm before throwing parts at it.

I have no idea what TCMPSLIP is. Any ideas? It seems to just bang back and forth, full on then full off repeatedly. Not even sure what that PID means.

Ah, the slip at the beginning and end of the datalogs I believe is normal. When the vehicle is at rest and idling, the TCCSLIP = Engine RPM. I believe that TCCSLIP is simply Engine RPM - Output shaft speed. Although labeled TCCSLIP, if there is any slip in the clutches, I believe it would show itself in TCCSLIP. TCCSLIP while cruising down the freeway is fairly consistent. It changes slightly with engine torque, but overall it seems to be more stable. Anyone know what a typical converter slip would be at stall speed? This converter stall should be approx. 1900-2100 rpm. I would assume that stall does not mean zero slip (otherwise a TCC wouldn't be required). My guess is that the TCC isn't working and the slip I'm seeing is the natural slip of the converter at the RPM. Why the TCC isn't working, I have no idea. Could be in the transmission actuation/circuit/seals or in the converter itself (cracked piston, burned clutch, etc).

Thanks again for looking at this! Any and all input is much appreciated!
Joshua

[joecar]

Check for these:
- is TCC brake switch coming on by itself (it's in one of the TSTATE pids)...?
- is ABS detecting rough road and telling ECM/TCM to disengage TCC...?
- are any misfires occurring (which causes ECM to tell TCM to disenage TCC)...?

Also there is a pid GM.TCCMODE which may be interesting, log this also.

4L80E/85E has ISS sensor, so also log GM.TIS and GM.TOS.

Also log throttle position, GM.ETCTP.

[joecar]

Post tune and log files as Erik said above.

[joecar]

GM.TCMPSLIP is a counter, it counts individual slip events.

[joecar]

Log GM.TSTATE03 for TCC brake switch state.

Log GM.TSTATE09 and 10 for TCC off reason.

Log GM.TFMPRS to see what line pressure is doing.

[jlane330]

Here is the tune (essentially stock, slightly decreased shift times (10% quicker), increased shift pressure (7%), decreased torque reduction (15%)). The rest is factory stock parameters.
20158

[jlane330]

Here is one of the two datalogs from yesterday.20159

Appears that there is a size limit for uploaded files? The other is slightly over 2MB.

[jlane330]

Check for these:
- is TCC brake switch coming on by itself (it's in one of the TSTATE pids)...?
- is ABS detecting rough road and telling ECM/TCM to disengage TCC...?
- are any misfires occurring (which causes ECM to tell TCM to disenage TCC)...?

Also there is a pid GM.TCCMODE which may be interesting, log this also.

4L80E/85E has ISS sensor, so also log GM.TIS and GM.TOS.

Also log throttle position, GM.ETCTP.

- I don't know about the TCC brake switch. Is this the same as the brake switch on the pedal that turns the brake lights on, or something different? I can't find a PID for TSTATE in V8 BBX...
- I don't have ABS in the van anymore. I removed it completely and replumbed when I converted it to 4wd. I will say that this all started occuring immediately after working on the slip yoke/u-joint. I replaced the slip yoke and a u-joint as I was getting a vibration from my d-shaft. May be purely coincidence. I still have a vibration and need to investigate further. I drove in 3rd gear today for logging, up to 70+ mph, and it felt much smoother than yesterday when I was in 4th gear. Need to reconfirm this by driving again...it was after the fact that I realized it.
- I don't notice any misfires while driving, and am not getting any codes. Being a D'max, how would I check for misfires more thoroughly?

I also can't seem to find GM.TCCMODE in V8 BBX. I am looking in E35A and T42.
I was logging TIS and TOS, sorry I didn't plot them. The data should be in the logs currently.

Throttle position...doesn't respond either. I was logging TP, and it didn't work. I can't find GM.ETCTP.

I don't understand why V7.5 has so many PIDs but none seem to work for the TCM. V8 doesn't seem to have the same PIDs available. What am I doing wrong? I'd like to be logging the right stuff...

THANK YOU!!!

[jlane330]

Had a chance to do a quick test drive. First datalog is while transmission is in 3rd gear (mostly, I did shift to 4th manually a couple times, but overall it was 3rd- see data current gear). I happened to log TSTATE3, which ends up is a bunch high idle switch states, etc. I do have a high idle switch installed (GM parts plugged into GM factory harness, new switch as of a few months ago). Why does the switch bounce around on/off? Strange. I assure you I was not playing with it while driving. I also don't understand what's going on with the brake apply, etc PIDs.
20162

I then shifted to D4 and came back. Same crazy High Idle Switch crap. Hmmm...
20165

Could it be that a vibration is making the switch contacts bounce in the High Idle switch? Maybe I need to disconnect the switch and see if it fixes the issue. Seems silly, but in general I'm not opposed to trying stuff like this. I do have a small vib in the driveline right now that needs sorting out. Not sure what that's all about.

Edit: I did confirm that the High Idle switch PID responds when I press the switch on the dash.

Any other suggestions? There are a lot of PIDs in the data logs. Not sure what all of them are, wanted to record as much as seemed to make sense.
THANK YOU!!!

20160
20161

[jlane330]

Sorry to overwhelm with data here, and possibly dumb posts. This High Idle switch stuff is strange. It appears to be semi-correlated with engine RPM or torque, no? Almost appears that if the torque exceeds a level, or the RPM hits a level, it sets the high idle switch. No idea how this might affect the transmission lock-up or slipping, if at all, but strange none-the-less.

I left the horizontal cursor at the crossover of point where RPM = High Idle (mostly):
20167

[joecar]

Here is one of the two datalogs from yesterday.20159

Appears that there is a size limit for uploaded files? The other is slightly over 2MB.

This log shows (on V7 scantool Data tab):
1. TCC Control (i.e. PWM) Solenoid Short to Power Test: failed.
2. TCC Enable Short to Power Test: failed (this is for 4L60E/65E/70E only, not used for 4L80E/85E).
3. Trans Line Pressure Short to Power Test: failed.

I don't know if those are meaningful, but you may need to check/test the wiring for 1 and 3.

Also, I see that the pid GM.TPS shows 99.6% always... this is a problem.

[joecar]

BTW: when TCC is locked, the TCCSLIP pid should show zero rpm slip.

[joecar]

High Idle Switch... I'm not familiar with that, what is it and how does it work...?

[jlane330]

This log shows (on V7 scantool Data tab):
1. TCC Control (i.e. PWM) Solenoid Short to Power Test: failed.
2. TCC Enable Short to Power Test: failed (this is for 4L60E/65E/70E only, not used for 4L80E/85E).
3. Trans Line Pressure Short to Power Test: failed.

I don't know if those are meaningful, but you may need to check/test the wiring for 1 and 3.

Good observation. I noticed those too in the logs. When I first started logging and monitored the data via the handheld, everything was a PASS IIRC. I try to look over all the data prior to spending time driving around. Anyway, I don't know what all those mean either. Any ideas?


Also, I see that the pid GM.TPS shows 99.6% always... this is a problem.

Yeah, so that clearly does not log throttle position on the D'max. The may have forgotten to remove that PID from the logs I took last night, but there is a PID that does show throttle position. I think it ended up being TP_A IIRC.


BTW: when TCC is locked, the TCCSLIP pid should show zero rpm slip.

That's my assumption too. At least it should be significantly less than what it is right now. Sure seems like the TCC tries to engage but the slip never changes.


High Idle Switch... I'm not familiar with that, what is it and how does it work...?
High Idle Switch is a physical switch on the dash that I can push and it will kick the idle speed of the engine up to 1200 rpm I believe. I added this when I added the engine drive air compressor, to increase the CFM output. It'll also be handy for charging the batteries a bit better when winching (whenever I get the winch installed...was supposed to be working on that until this trans stuff came up). Anyway, if engaged, High Idle turns off when the brake is depressed or the switch is pressed again.

[jlane330]

Quick update:
Still working on diagnosing this. Been a bit of a wait for parts and a pressure test gauge. In the mean time I did wire in a manual switch to lock the converter clutch. Test drove it in both 3rd and 4th and locking the TCC manually with the toggle switch resulted in a VERY slight (maybe 10-20 rpm) drop in rpm, but there was still a lot of slip happening even under light load. Romp on the skinny pedal and slip would jump to hundreds of rpm. I think I can safely say that the TCC is not holding, just not sure why now.
Noticed the other day a new phenomena. Occasionally at idle I hear a buzzing sound coming from the converter/bell housing area. Sounds like a vacuum pump, but it's clearly from the bell housing. It comes and goes, and I assume it could be related to line pressure, the converter or maybe the pump itself. It's pretty loud, and distinct. The buzzing seems to vibrate the seats and floorboards slightly too, enough to be felt.
On the suspicion that it is the converter, I ordered a custom one from Precision Industries (in TN) today. I'll plan on swapping it ASAP and then collect some new data logs with the TCC locked.

[joecar]

It sure sounds like TCC is not holding... (if it doesn't hold you should see TFT temperature on the high side).

The buzzing sound is most likely the pressure regulator rapidly cycling at some pressure (resonance between fluid, valve, spring).