mjm-1957

Make sure that a PF63 filter is on there and that they used 5-30 oil and not 0-20. I work on the line at a GMC-Buick dealer and can tell you that the oil changes are usually done by the newest inexperienced ****** heads that they can find. Mistakes happen every day. I would not let half of them put air in a bicycle tire. Just something to check.

Check for trouble codes.

Get an accurate dvm and check alternator output right at the output terminal of the alternator and then check at the battery. Are they close? If not perform a voltage drop test on all battery cables. Disable the fuel injectors and crank the engine while monitoring the voltage drop.Those are noted to have questionable battery cables. Gm doesnt want more than .5 voltage drop on the cables . We change a fair amount of them at work.Also that battery sensor is supposed to be on the negative battery cable. Ground connections are another constant source of problems. Loose or corroded grounds will drive you crazy.

Do you have the vin from the truck it came out of? I can VIS it and give you the size and year.

Time to check those head gaskets.

Did you have the customer satisfaction program number 17456 done? It is for this exact problem? Retainers were not made correctly and allowed the retaining nuts to back off. Unfortunately this expired 2/29/20. Are you the original owner? You should have gotten a notice to have it repaired from GM. We were doing them a few years ago at my dealer.

I hope that you can read this. I fix cars much better than using a computer.

Document ID_ 803013.html

Your parts buddy is wrong, See if code p1626 or p1631 is current or history in the PCM.That truck has theft deterrent and that could be giving you your problem.I dont know how to send a link to something but if you have access to GM si this is the document ID number that should point you in the right direction 803013. The TSB number is 01-08-56-002A

The squeaking is never good, could be a roller let go on one of the lifters and is grinding down the cam lobe.

Check the mega fuse on top of the battery.

We change a lot of starters on those trucks at work.

Pin 14 is circuit 2500 dark blue wire is high speed communication circuit, you were correct, pin 13 is blank on your model,sorry about that. If I could post the schematic you would have seen that. These old eyes aren't as sharp as they used to be. Glad ypu got it going.

Pin 13 is high speed communication circuit 2501. I cant figure out how to upload the schematic. If you have access to service information from GM the document ID number is 3627766. That should get you talking with the TCM again.

Make sure the connector at the transmission is fully seated and there are no bent or backed out terminals, the scanner should see the TCM at start up.If that checks out okay make sure the passthru in the case is fully seated and that the retainer is fulled locked.It should snap and click into place when fully seated.