How did others fix this U1255 code?

[bai78]

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

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°

[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.