A Stack of ECUs Tahoe Won't Program

Michael Mobile Technician Utah Posted   Latest  
Case Study
Programming
2003 Chevrolet Tahoe LS 5.3L (T LM7) 4-spd (4L60-E)
Programming Failure

After doing some work at a shop 4 hours South of my location, I did some warm calling to dig up some local work before heading home. It would be too late by the time I got home and I don't get down there too often. I went to a shop that had two jobs that were plaguing them. One was a Tahoe that would not program a replacement ECU. Hence a stack of ECUs. The other a Jeep Liberty that I will report on at a future time.

So I figure this Tahoe would be a slam dunk. I do these all the time. On first attempt I get the "severe error" code. I look at the dashboard and see an aftermarket radio. The steering wheel has controls for volume. So maybe the aftermarket radio is tied in the comms system. I pull the radio fuse and try again. Same error. So I can either remove the radio and look for the offending module / part or look for another way. I am able to reach under the dash and unwrap the splice pack. Then I remove the comb from the pack and jumper the ECU data line. Attempt programming and Success!!!! One picture is of removed comb. Other picture is of splice pack socket. Hope this helps others faced with issue.

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Sean Technician
California
Sean
 

So you jumpered that back to ECM or the ALDL?

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Michael Mobile Technician
Utah
Michael
 

Sean, I used a breakout box tied to OBDII for the power and ground. The pass-through was also connected to the breakout box. The yellow wire was jumpered to the corresponding pin in order to get communication.

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John Owner
New York
John
 

Michael, Must be something in the air lately. I had two early GM products that would not program due to aftermarket devices "chattering". One was easier to remove the radio and the other I jumped out the splice pack like you did. Nice work.

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Philip Educator
California
Philip
 

Thanks, Michael. I think I will add this tip to my network class. I don't think I would have remembered that splice pack, though I have used it before to troubleshoot a network problem after a transmission replacement. The G103 ground at the rear of the engine broke when the motor tipped back and the class 2 bus had 7.6 volts on it at all times with the missing ground.

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John Owner
New York
John
 

Phil, Those of us that program regularly always are on the look out for add on aftermarket devices, radios, GPS, trackers, etc. One of the first things I do is look at the DLC and make sure there is no aftermarket wiring and that it doesn't have a jumper DLC piggybacked. Usually, you can spot this as a DLC with all 16 terminals populated. Granted, some really late model vehicles will have a…

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Philip Educator
California
Philip
 

Thanks, John. Do you allow ride-alongs? John Anello doesn't do it anymore. I'm looking for the opportunity to learn these idiosyncrasies. I don't know if I will need to go back to something like this or not, but I definitely feel like I don't want to spend what remains of my career teaching to a computer. I'm doing it for now because I have a good job with good benefits, but if O'Reilly keeps…

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John Owner
New York
John
 

Phil, Yes, I do ride alongs. There have been several techs that have rode around with me. Some have started their own mobile business as well. Once this COVID issue clears up I would look forward to having you come on out and ride along. I believe the only way to learn is to do. It speaks volumes to your character that you want to experience what we see in the field. I wish more trainers…

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Andrew Owner/Technician
Iowa
Andrew
 

This is how I always program Trailblazers, they always seemed to be the worst offender.

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Geoff Diagnostician
Hawaii
Geoff
 

Thanks Mike. Not that I would be able to find it, but I think GM had a PI or TSB or two about that way back then. Even without A/M butchery, some cars needed chatter off the network to accept programming.

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Michael Mobile Technician
Utah
Michael
 

Geoff, The software at times will make you aware of the issue like in the case of the Trailblazer. Other times you are on your own. The TIS tech line told the shop that it was defective ECUs. After 3 of them it became very unlikely.

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Francis Owner/Technician
Virginia
Francis
   

Nice hack Mike ! I'm frankly surprised GM-Arlington kept that old ALDL/C ("OBD-1") on the harness-- we used those old 12-pins a lot back in the day (80s-90s) to pull diags. Applying GND to that 8192 TTL data stream nuked that chatter -- those Delphi ECUs are normally easy to program/reprogram (different story with some of those vintage BCMs -- write once).

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Michael Mobile Technician
Utah
Michael
 

Hi Francis, The connector that appears to be a ALDL in the picture is the splice pack that ties one part of the network together. All the terminals are connected together when the comb is placed into the socket. The white piece on the floor liner is the comb.

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Nolan Technician
Bahamas
Nolan
 

These stories keep me on the edge of my set as I read them very informative thanks so much for your time, sir!

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