2003 Silverado 2500HD Duramax with 2005 6.6L Duramax Swap Issues

W221.176 · April 15, 2018

Hi Everyone,

I am new to the late model GM diagnostic platform, although I have been reading and absorbing all I can on the subject. I have owned many GM vehicles, wrote EPROMs for 86-87 Grand Nationals in the early 1990s, and have owned a an C4 LT5 ZR-1 Corvette and 1997 LS1 Corvette when they came out, which I think was the first GM vehicle with the dot matrix cluster used in many other models in years to come. I am familiar with the fundamentals of modern diagnostics, and work on Mercedes-Benz vehicles as a hobby (the only non-Domestic brand I have ever owned). Knowing how they work, which is more complex in many ways with the anti-theft technologies built into them and control modules for anything and everything, I had have been asked by someone to look at his truck that has been giving some issues.

It is a 2003 Silverado W/T 2500 and has had the engine changed for an unknown reason before he purchased it. The engine's emissions label is from a 2005 and the PCM reports a 2005 VIN, indicating the entire engine and PCM/TCM was installed into the truck. The truck starts and runs great, however it has been exhibiting a few issues that he asked me to look at that are problematic for him:

1) When the speedometer is reading 55mph, the truck is going around 72mph. In the process of looking for hints that may cause this, I noticed something unusual - the tach went to 6k RPM with no redline. I assume there are a number of possible causes for this with the simplest being that the cluster was changed as the original was defective, but a second hand cluster was installed from a 2500 gasoline truck. The transmission temperature gauge was present, and from my research it should be a 5k RPM tachometer with a 3.5k RPM redline. Also, the oil pressure range was 0-80, and it appears the correct cluster should range 0-120psi. After this discovery, the owner purchased a second hand diesel-correct cluster and had the odometer calibrated up to match the one in the truck (the diesel cluster was nearly 100k lower originally, and the vehicle history shows the reading on the gasoline cluster should be correct and there are no discrepancies or odd jumps in readings - so that is the only thing to go by). The motors were tested in the new cluster when it was calibrated with the mileage, and were tested fine. This cluster was tested when first acquired before mileage correction in the truck, and still read the incorrect MPH.

2) A Service Air Bag indicator is on, which from what I understand is fairly common, and could be a sensor, but was advised by a dealer it could be the same things causing issue #3 below

3) Service Brake System is coming on after a few miles with a very long duration of chimes, illuminating the ABS, BRAKE, and dot matrix warning on the cluster. This happens a few milies into a trip.

4) The fuel gauge is reading inverse of what it should (not sure if related to other issues) but when empty, it reads a tick above full (don't ask how I know!) and when you fill the truck the gauge moves closer to Empty.

An independent mechanic replaced the "ABS module" (I don't know the details on this) attempting to fix the ABS and BRAKE warnings and long chimes, and it did not change anything, as the fault is still there.

Afterwards, it was taken to a dealer to diagnose. Dealer diagnosed as PCM VIN indicated a 2005 year vehicle and vehicle is a 2003. The EBCM and Air Bag module have the truck's correct 2003 VIN entered. The VIN mismatch is causing the ABS and Air Bag warnings to be displayed. When asked if it could be fixed, the response was "It CAN be fixed, yes. Are we allowed to do it? No." (I assume changing the VIN in the PCM violates the either the dealership or GM policy or perhaps they did not want to attempt to fix it if it failed or caused other issues).

Therefore, I have been asked to look at it, and from the research I have done, the VIN can be corrected in the PCM using SPS if replace/reprogram is selected. However, if will attempt to flash the PCM with the latest flash for that VIN. If it attempts a flash, I am 99% certain that either the flash will fail because the PCM will not accept it (I have not looked but I am assuming it uses a different part number for the PCM). If the flash is successful, the PCM could not start the truck as the logic in the flash was not designed to run that model Duramax engine.

Therefore, my questions are these -

What options do I have to change the VIN without flashing the engine code on the PCM?

Is it likely the VIN mismatch is causing the ABS/EBCM errors and/or Air Bag warnings?

The tire size matches the ones listed in the door jamb, so it has the correct tire and has not been lifted. What module is the speedometer calibration done?

Is a Tech2 the best device to perform these tasks?

Thanks to anyone that could offer and sense of direction!

EDIT: AFTER READING THE POST FROM THE ADMINISTRATOR REGARDING QUESTIONS ABOUT VEHICLES NOT IN AS-SHIPPED CONFIGURATION ARE NOT TO BE POSTED HERE, I ASK THE ADMINISTRATORS TO PLEASE MOVE THIS POST TO THE APPROPRIATE FORUM. THANKS, AND SORRY FOR THE INCONVENIENCE.

Doug_Scott · April 15, 2018

What engine did this truck originally come with? Was the entire drivetrain swapped? What gears are in the rear end? You should be able to get all the RPO numbers from glove box door to find out what this trucked started life with. Speedo readings can be altered by transmission, rear axle gears, and/or tire size. To be off as much as it is is not going to be tire size, and if it's gears, it must be programmed for 4.10 gears but has 3.08 gears. You are going to need do a complete survey of what you currently have and what is expected to be there by the ecm/bcm/tcm.

W221.176 · April 15, 2018

4 minutes ago, Doug_Scott said:

What engine did this truck originally come with? Was the entire drivetrain swapped? What gears are in the rear end? You should be able to get all the RPO numbers from glove box door to find out what this trucked started life with. Speedo readings can be altered by transmission, rear axle gears, and/or tire size. To be off as much as it is is not going to be tire size, and if it'

Good question. Here is the SPI.

Doug_Scott · April 16, 2018

Truck was originally a 6.6 Duramax with Allison 5sd, 3.73 rear axle, manual transfer case, 9800 or 9900(cant recall off hand) lb towing, and came with the standard 245-16 tire size.

With the vin from the ECM you could ask a dealer to run the vin to see what that 05 came with stock.

W221.176 · April 16, 2018

5 minutes ago, Doug_Scott said:

Truck was originally a 6.6 Duramax with Allison 5sd, 3.73 rear axle, manual transfer case, 9800 or 9900(cant recall off hand) lb towing, and came with the standard 245-16 tire size.

With the vin from the ECM you could ask a dealer to run the vin to see what that 05 came with stock.

Assuming the other garage changed the EBCM, will it need to be coded? I was also told the hubs were changed (but ironically 4WD will not engage and I haven't researched that). Where would I need to go to check the gear ratio it is programmed for?

Thank you for your help!

Doug_Scott · April 16, 2018

I do not know about what vin number can do to the ECM, and would imagine dealers will not reprogram it is fear of being accused of "vin washing". Do you have access to the original engine or original ecm/tcm? Really have to wonder why they did not just change the engine itself and swap sensors over from the 03 engine.

I wonder if the transfer case is the original one or if it is the automatic transfer case and if it is the required wiring may not be present. If you can locate an ecm at the wreckers, perhaps you could reprogram the vin into it to see if it changes anything. You would still have the current one in case it screws up the wrecker one. You will have to go through the security relearn sequence though.

The speedo difference can't be just a gearing issue. Mathematically the truck would need to have a 2.80 gear. 72 to 55 is a huge jump.

You could try contacting Justin at blackbear regarding updating vin and what it may impact. You have your hands full with this one, I would just do one thing at a time. Can you contact the owner that did the work?

W221.176 · April 16, 2018

The person who present owns it has only had it perhaps a month or two. I think that he was so impressed by the way it ran and the power it had (and perhaps the asking price, in which I have no idea what it was) and figured the warning lights could be addressed fairly straightforward. If I recall correctly, the current owner has tried to call the person that he purchased it from and has not receive and response or reply (which is fishy in and of itself)

I have heard of many of these being done, but I don't know anyone personally. How would I go about getting in touch with this "Justin" gentleman?

Thanks!