How did others fix this U1255 code?

[bai78]

I installed a new pcm and was able to successfully do a CASE relearn. Now I am having start problems, as in not at all. It turns over & wants to crank but it is a no go. :shock: I've disabled the VATS & still nothing.

After scanning the PIDS, it seems that in the VTD there is something enabled with regards to the fuel system whereas everything else is either disabled or no in the field.

PRI CAPTION DESCRIPTION VALUE UNITS MIN AVG MAX PARAMETER SYSTEM
1 VTD-VTD1 Vehicle Theft Deterrent Fuel Cont No . No No No GM.VTD Fuel

1 VTD-VTD2 Vehicle Theft Deterrent Fuel System Enabled . Enabled Enabled Enabled GM.VTD Fuel <===HELP

1 VTD-VTD3 Fuel Disabled No . No No No GM.VTD Fuel
1 VTD-VTD4 Auto Learn Timer Not Active . Not Active Not Active Not Active GM.VTD Fuel
1 VTD-VTD5 VTD Fail Enable Not Active . Not Active Not Active Not Active GM.VTD Fuel
1 VTD-VTD6 Password Learning Disabled . Disabled Disabled Disabled GM.VTD Fuel


I've searched through some older threads & some have dealt with various codes like U1255, but didn't really have a clear post for resolution. It seemed it had it one day & the next few post all was resolved. :?

HELP! HELP! HELP!

[Taz]

Hello bai78,

What is the vehicle application ? What engine / transmission ? What PCM and OS ? Is this a "swap" or does the PCM need to communicate with a BCM, etc ?

Most of my experience is with the Gen III family of engines and LS1-B style PCMs .... FYI.


Regards,
Taz

[bai78]

This is a conversion for my GMT400 '99 Tahoe.

- 16263494 black box (09365085 os) to 12200411 pcm (12212156 os)
- 5.7L (L31) / 4L60E

[Taz]

Hello bai78,

Just want to make sure I understand correctly before making any suggestions …..

Your ’99 Tahoe was originally equipped with the L31 5.7 L and 4L60E ?

You are undertaking an “0411 swap” – upgrading your black box Vortec PCM to an LS1-B style PCM (12200411) using 2002 OS 12212156 ?

If this is correct, I then take it you are using a “base tune” from an ’02 Express van – that was originally equipped with the L31 5.7 L and 4L60E ?

If the above assumptions are correct, I also assume you wish the new PCM to communicate with your existing BCM ?


Regards,
Taz

[bai78]

Correct

[Taz]

As a disclaimer, I don’t do black box Vortec tuning, and have never had a customer request an “0411 swap” - I have never done one.

I will assume you did the conversion from the black box Vortec PCM to the LS1-B PCM yourself. If so, you will have wiring diagrams (pinouts) for both PCMs - and will have moved one pin at a time, from the old PCM to the new one.

What I’m going to suggest may amount to overkill - but it should work. There are Forum members that have expertise in this type of PCM swap – if they see this post, perhaps they may have a short cut, or directly applicable suggestions.

You indicated you wanted the new PCM to communicate with the existing BCM. I’m going to assume you also want your existing VATS to function – same truck you’ve always had, but with a superior PCM and OS.

You also indicated you had the engine running, but problems arose after a CASE learn was executed.

OK …. I’m going to suggest starting from a “clean sheet” – full reflash (which you have probably done at least once).

The ’02 Express van “base tune” you have, uses a Class-2 VATS configuration. Older applications used a PWM VATS configuration. Your ’99 Tahoe is of course from a GM transitional year. Pickups in ’99 used Gen III engines with LS1-B PCMs, and a Class-2 VATS. Your Tahoe used a Gen I based engine, and a Vortec PCM.

Hopefully, you already know, or have manual that indicates, which VATS configuration your Tahoe originally used - G1201 (Anti Theft Configuration) needs to be correctly configured to this.

I generally prefer to bench program PCMs to eliminate electronic interference or background “noise”. You probably don’t have access to a bench top harness, so the next best thing is to isolate the PCM while installed in the vehicle. Sometimes removing fuses is sufficient. In your case, you have just moved all the PCM pins, so you are familiar with how simple that task is – so I would isolate the PCM that way.

Steps:

1. configure G1201 to the appropriate value - in the tune you previously flashed and resave the tune
2. disconnect the POSITIVE battery cable – touch this cable to ground (to eliminate any residue energy)
3. temporarily remove the pins from the PCM harness connectors that go to the BCM and ABS systems (to eliminate interference / noise)
4. reconnect the POSITIVE battery cable
5. prior to reflashing the tune – in the Tune Tool - Flash\Program PCM calibrations\ - uncheck (don’t use) the “use high speed” box (also helps eliminate noise). Also confirm the “Ignition cycles before VAT relink” box is set to zero
6. reflash the tune - don’t touch anything during this process (I try not to breath !)
7. when the reflash is complete - and you are prompted to disconnect / turn off ignition – wait a moment (15 seconds or so) to make sure the process is actually complete – then turn off the ignition.
8. take a 5 minute break (well deserved)
9. disconnect the POSITIVE battery cable
10. reconnect the BCM and ABS pins to the PCM harness
11. reconnect the POSITIVE battery cable
12. take another 5 minute break

At this point, you should be good to go. As an overly caution person, I would cycle the ignition “on” for 5 minutes, and then “off” for 5 minutes – prior to attempting to start the engine. If G1201 was properly set, the PCM and BCM should now be linked.

Start the engine and let it run for a few minutes. Again, as a cautious person, I would do this 3 or 4 times. (If the engine fails to start initially, or on subsequent attempts – try another VAT relink via the Tune Tool – Flash\PCM security\VAT relink option).

If the above is successful, initiate a CASE learn sequence (as you had done previously).

I know this seems long and tedious, but the intent is to eliminate variables in a step wise progression. The question is, did your current problems arise as a result of the initial reflash, VAT relink (attempted relink), or the CASE learn ?

Good luck ...

Regards,
Taz

[bai78]

Thanks Taz for the detailed info.

Out of curiosity earlier I did enable the VATS with class II as well as do a relink. Low & behold, no more VTD codes. While researching I stumbled across info that stated '98 - '03 Tahoes & '98 - '06 Express Vans share the same class 2 VATS. I figured it couldn't hurt to try & see what happens.

All this troubleshooting has taken a toll on the battery. Now it is out of the truck & on a charger waiting to go back in for a crank.

[joecar]

You used the scantool to do VATS relink... :cheers: good deal.

[Taz]

Nicely done !! I got to ramble on, and it turned out to be an "easy" fix !!

Thanks for posting the outcome, and the info on the Class-2 VATS ... will squirel that away for future use.


Regards,
Taz

[joecar]

That info is still useful to someone who is doing a 0411 install from scratch.

[bai78]

I connected the battery after it was charged and still wouldn't fire up. One code gone & another pops up in its place. :doh2:

U1016: Loss of Communications With PCM

Seems I need to do a security relearn procedure.

[Taz]

Chasing “Gremlins” can consume a lot of time and resources …… we’ve all been there.

I should have mentioned battery voltage in the previous posts. Most 12 volt automotive batteries when new hold at least 13 volts with a full charge. PCMs and BCMs can be “fussy” about the voltage they have. Personally, I won’t flash a PCM if the battery source has less than 11.5 volts at the start of the session, because as you have discovered, battery voltage can be quickly consumed.

I have various OEM manuals for Gen III applications (singlehandedly keeping Helm publishing in business !) - but I don’t have one for your ’99 Vortec Tahoe. The BCM in ’99 Gen III pickups needs to have 9 to 16 volts to function appropriately. I would suggest applying my 11.5 volt guideline to this also.

Hopefully you find the solution sooner, rather than later. Ultimately, you may end up starting with the “clean sheet” I mentioned a few posts back - if issues cannot be consistently resolved. Appropriate battery voltage is a factor in flashing the PCM and relinking the VATS.


Good luck …

Regards,
Taz

[bai78]

When the charge completed, it was holding 13.01 ish volts.

It's interesting, just got back from hooking up the scanner & no more U1016. That was odd as I was going to do the security relearn procedure but noticed that the light went off after a few seconds. This prompted me to drag out the laptop & take another look. Again, nothing as far as VATS/VTD codes....just the same C0235 ABS codes.

Now I am faced with the possibility of a bad PCM. Well I've always been faced with that possibility from the beginning. Would a bad pcm still connect, scan, reflash, etc....? As stated before it fired up when I connected it as well as for the CASE relearn. I kinda know the answer, but do they just get up & die on you all of a sudden?

I do have a spare 12200411 pcm that hasn't been flashed yet. However, I would like exhaust all possibilities before purchasing another VIN license.

[Taz]

Others may have different experience with PCMs, but I have had very few actual PCM failures. They are durably constructed and often have Intel or AMD flash chips inside - just like a Laptop / PC.

I try and take a “scientific” approach (can’t think of a better description) - isolate variables, one change at a time, record changes and observed results.

Now that you have a fully charged battery, I would embark on the “clean sheet” approach - detailed in previous posts. This should ensure the PCM is properly flashed - no interruption in data transfer, etc.

After that, encourage the VATS relink process – key on / off for 5 minutes.

Then try and start the engine. There is no rush to do a CASE learn – sometimes these are omitted and the vehicle will often run “OK”.

If the engine starts, let it idle for at least 5 minutes. Then repeat this several times - to ensure the VATS link is actually established, and holding.

After you are satisfied with the above, attempt the CASE learn.

This way, if / when issues arise there are fewer variables to consider, as each phase must be successfully completed (and tested several times) before moving on to the next phase.

Don’t blame the PCM just yet ……


Regards,
Taz

[bai78]

I was out scanning again & selected some pids. A few things caught my eye:

1. Battery Voltage showed 0 across the board.
2. Engine size had 5.3.
3. Ignition timing advance for #1 cylinder is -64°

:nixweiss:

[Taz]

Your PCM is a “0411” with an ’02 OS.
Was the PCM purchased from an auto recycler, or of unknown origin ?
Was the original vehicle that PCM was from a 5.3 L Gen III ?
Did you initially conduct a FULL reflash of the PCM (OS and Calibration from ’02 Express) ?
Or just a Calibration only flash ?


Regards,
Taz

[bai78]

This particular pcm was purchased from another forum member who had this 0411 running in his GMT400 Tahoe. I am not certain where he acquired the pcm. His tune had an '02 extended cab VIN with the 4.8L.

Yes, I did a full reflash of the OS & calibration. Should this operation be done again? Yeah, I know the answer.

[Taz]

OK … initial full flash should have loaded the OS and calibration from the Express. Something is not right ….

Where did you get the ‘02 Express tune from ?

There is one on the Holdencrazy site …. not a bad idea to download it …. then compare it to the tune you have …. just to make sure you are starting from a “stock” tune …

Not sure if you’ve ever used the “Load alternate calibration for comparison” function in EFILive Tune Tool …. works fantastic. You can configure it subtract (for tables with values) the Alternate calibration from the Current calibration - or the reverse, whatever your cognitive preference !

And yes, I think it is “clean sheet” time - start fresh, full reflash - but not before you confirm the validity of your base tune.


Regards,
Taz

[bai78]

The base tune was downloaded from the Holdencrazy site. I just gave it a whirl & the normal (non highspeed) flash would fail. It would repeatedly attempt to replace/retry blocks. The highspeed would take the tune & calibration though. I'm sure it is supposed to work either way, right?

I have not used the comparison function as of yet but will explore that option.