WTH checksum failed after flash on 2 pcms, now 2 dead pcms

[joeygc5]

I've never worked on a vehicle with so many Gremlins.
Flashing using V8 2..2.258
Firmware 2.07.64
LS1B controller with OS #12606807
2006 GMC Sierra C1500Vortec Max with a small camshaft. I loaded the initial tune with some problems, had to try three times to get connection to PCM, and it drove decently well and no idle issues after the tune. After the tune I could log with no issues or comm problems. I then go to load a revised tune (same original OS) and at he end of the Cal flash I get a "Checksum failed" error. I'd never seen the error before and after looking all through the search threads I just turned the key off (truck had ignition on for over 30 minutes waiting for checksum retry or status message update).

Well I go to start the truck and PCM is in dead poll mode, no fuel pump, no cranking, nothing. I pull the PCM connectors, check all power and ground wires, as well as data wiring to OBDII port with no issues found. I had another PCM and hooked it up to the truck, truck cranked over but wouldn't start, b/c OS difference, with no issues (4.8 Van pcm). I then tried the PCM status and security runs on 2nd PCM, no issues, then I read from the 2nd PCM with no issues. So I go to full flash the original tune in the PCM and it goes all the way through the erase and write functions, then stops at "Checksum Failed" again. I left the ignition on for over an hour with no change after he error message. I had the truck on a charger, AC fuses and anything that might affect the tune transfer was unhooked/disabled. I then had to just turn the key off as the software would only let me either stop writing, or close the window. Now the 2nd PCM is in the same dead poll'esque state. I even tried the power and ground battery wires short for over 90 seconds to clear any BCM fault, with no outcome.


Any suggestions? Tune is attached also

Cliff notes "Checksum failed" message has resulted in 2 dead PCM's and 2 used licenses with no running vehicle. Truck won't even crank over with either PCM, but truck will crank with a spare PCM from another DBW vehicle. Then thinking it might be my V2, I read and wrote to an LS1B, E40, and E38 controller with no issues.

[GMPX]

Given it is a pre CAN bus vehicle please make sure they have no aftermarket devices that are wired in to the VPW communications bus, if there is anything on there that will not stop communicating during the flash then you will see the sort of errors you are getting. It is not normal but also try the BCM and Radio fuse.
When in 'dead poll' that means the PCM's will be recoverable, if you have access to another vehicle or a bench harness you could try bringing them back to life that way.

[joeygc5]

Used a bench harness and got third pcm running in truck fine. Both previous pcm's wouldnt even show up on flashscan. So progress one way and taking it in the shorts the other.

[GMPX]

Did the two previous PCM's work on the bench harness ok as well?

[joeygc5]

No on the bench harness I cant get anything on the auto search, just the flashscan as end of path, for lack of better description. Connection of now in truck pcm, or another spare DBW pcm has no issues connecting. Just the original and then the 2nd pcm are basically just nonexistant to my flashscan.

[GMPX]

I cant get anything on the auto search,
When you say 'auto search' I'm not sure what you mean, but when a PCM does not have a completed flash in it they are in a reduced function state. What you should try is a Full Flash on the bench to see if they come back to life. If you are using V7.5 it will tell you at the start the PCM may not have a complete flash, just click to continue on.

[joeygc5]

When you say 'auto search' I'm not sure what you mean, but when a PCM does not have a completed flash in it they are in a reduced function state. What you should try is a Full Flash on the bench to see if they come back to life. If you are using V7.5 it will tell you at the start the PCM may not have a complete flash, just click to continue on.

If I'm using V8 and got to the tune utility, read utility, or full flash utility; the two bad pcms won't even show up. Even if I try using the auto detect function. If I connect to the currently in use pcm, or a spare DBW pcm the pcm is shown as soon as I go to the same read/cal-flash/full-flash utilities. If I'm using V7.5 I can't connect in the same situations, even trying to use the pcm security or pcm status functions, nothing is shown but the Flashcan V2 when connected to the 2 bad pcms. This is using an EFILive benchtop harness also.

[GMPX]

It sounds like they must have failed during the very early stages of a Full Flash?

[joeygc5]

It sounds like they must have failed during the very early stages of a Full Flash?

Both pcms went through the sequence and stopped at the exact same time after writing to the pcm, but having the "checksum failed" alarm. Once geting the "checksum failed" everything just stopped dead in it's tracks. Ive had comm issues before that were resolved by pulling the BCM or radio fuses, but nothing like this.

[joecar]

"checksum failed"

my understanding: sounds like the tune file you were flashing had been edited by some other tuning software (that added extra bytes to force/hack the checksum).

[GMPX]

Both pcms went through the sequence and stopped at the exact same time after writing to the pcm
Ok, but at what point? The start, the end, the middle? I know initially you said a Cal Flash right at the end, is that the same on both PCM's?

[joeygc5]

As far as I know it was at the end of process through observation. The pcm was connected> validations run> old tune erased>new tune OS file written> then checksum failed message appeared. I have no screen shots nor further info. Because watching my laptop with the PCM's in the vehicle (while tuning), the process stopped with both PCM's after the tune file was written (status display) and then the checksum failed message appeared. Then I wasn't able to do anything, no communication, no vehicle start, no finish of the tune process after the checksum error.

The truck is running and driving fine, idk what tune was in it, but it looked like a basically stock tune from the PE tables and timing maps.

[GMPX]

On these PCM's there is really only two things that will stop them being recoverable.

1 - Failure of a Full Flash within the first 20 seconds or so.
2 - A faulty calibration that causes the PCM to do an endless reset (divide by zero error it's called, can happen with speedo calibrations).

Given your situation it seems like neither of the above should apply. If it got to the end and the checksum failed then the flash finalisation would not have occurred, in which case the PCM should be in what we called "dead poll". Meaning it just sits there and broadcasts a message saying "I'm here but not 100% functional", kind of like a tortoise tipped on its shell, it's alive and kicking but not much else.

With a PCM in this state hooked up to a bench harness you should see one of the orange LED's on the V2 flashing about twice a second, that is the poll from the PCM to say it is not functional 100% but it can be bought back to life. Do you see that happening?

[joeygc5]

On these PCM's there is really only two things that will stop them being recoverable.

1 - Failure of a Full Flash within the first 20 seconds or so.
2 - A faulty calibration that causes the PCM to do an endless reset (divide by zero error it's called, can happen with speedo calibrations).

Given your situation it seems like neither of the above should apply. If it got to the end and the checksum failed then the flash finalisation would not have occurred, in which case the PCM should be in what we called "dead poll". Meaning it just sits there and broadcasts a message saying "I'm here but not 100% functional", kind of like a tortoise tipped on its shell, it's alive and kicking but not much else.

With a PCM in this state hooked up to a bench harness you should see one of the orange LED's on the V2 flashing about twice a second, that is the poll from the PCM to say it is not functional 100% but it can be bought back to life. Do you see that happening?

Connecting each "bad" pcm has the right side LED'S flash once then nothing and V8 is unable to auto-detect. Connecting good pcm constant LED flashing and no need to auto-detect as the V8 instantly recognizes.

[GMPX]

Where are you located out of interest?

[joeygc5]

Kansas City area.