Pcm trouble couldnt afford new pcm went to salvage do it have to be reprogramed to vin or can i reset it some way.

An internal computer problem. Read only memory. This is the factory defaults. These can't be erased by a tech. But can be by a system fault. You can get the computer online for about $160. Plug and play. Dealers 2 to 3 times this.

If you are sure the computer is the problem... remove the original one and it will have a tag on it with part numbers. Find one at a salvage yard and compare part numbers to make sure they are the same and it should work. The only thing that may cause issues is if the vehicle has a security system and a relearn/reprogram may be required

Have to see a dealer-- for that question

Who replaced it & why?
How was it tested?

I would assume it is blank

Has to be flashed to your build date & VIN #
then any updates

The dealers are just telling you thing's it could be , doesn't mean they are just going to replace all of those parts or you need all of them , Doing the diagnostic test procedures associated with the DTC - diagnostic trouble code are were they start . Take it to one an have it diagnosed .

You have to reprogramm the ECM. Here is a bulletin for this problem.
Subject:
Service Engine Soon Light On, P1680 (Reprogram or Replace PCM)

Models:
2004 Buick Rainier
2004 Chevrolet Trailblazer
2004 GMC Envoy
2004 Oldsmobile Bravada
with 4.2L Engine (VIN S - RPO LL8)

Some customers may comment on the Service Engine Soon Light coming on. Upon investigation, the technician may find a P1680 diagnostic trouble codeCheck the resistance of the accelerator pedal position sensors using the procedure in the appropriate Service Information for DTC P1680.

If the resistance of the accelerator pedal position sensor is within the specifications shown in the Service Information and the vehicle was built prior to the following VIN breakpoints, then reprogram the PCM with the latest calibration.

If the resistance of the accelerator pedal position sensor is within the specifications shown in the Service Information and the vehicle was built after the following VIN breakpoints, then replace the PCM. If the resistance of the accelerator pedal position sensor is outside the specifications shown in the Service Information, then continue with the diagnostics for DTC P1680.

VIN Breakpoints
• Vehicles built at Oklahoma City Assembly Plant - 46192755
• Vehicles built at Moraine Assembly Plant - 42315833

Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day.

You have to reprogramm the ECM. Here is a bulletin for this problem.
Subject:
Service Engine Soon Light On, P1680 (Reprogram or Replace PCM)

Models:
2004 Buick Rainier
2004 Chevrolet Trailblazer
2004 GMC Envoy
2004 Oldsmobile Bravada
with 4.2L Engine (VIN S - RPO LL8)

Some customers may comment on the Service Engine Soon Light coming on. Upon investigation, the technician may find a P1680 diagnostic trouble codeCheck the resistance of the accelerator pedal position sensors using the procedure in the appropriate Service Information for DTC P1680.

If the resistance of the accelerator pedal position sensor is within the specifications shown in the Service Information and the vehicle was built prior to the following VIN breakpoints, then reprogram the PCM with the latest calibration.

If the resistance of the accelerator pedal position sensor is within the specifications shown in the Service Information and the vehicle was built after the following VIN breakpoints, then replace the PCM. If the resistance of the accelerator pedal position sensor is outside the specifications shown in the Service Information, then continue with the diagnostics for DTC P1680.

VIN Breakpoints
• Vehicles built at Oklahoma City Assembly Plant - 46192755
• Vehicles built at Moraine Assembly Plant - 42315833

Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day.

DEALERSHIP HAS TO REPROGRAM THE NEW PCM.YOU NEED A GM SCANNER TO REPROGRAM NEW PCMS IN GM VECHICLES THE GM VECHICLES FROM 1996 UP TO 2011 HAS TO BE REPROGRAM AT DEALERSHIP, HOME MECHANIC CANT REPROGRAM IT.YOU NEED GM TECH 2 SCANNER.

If you key has a chip in it, you will probably have to get your ECM reprogrammed with the proper VIN, since it no longer matches the original VIN on your Vehicle. I don't think the dealer would program your keys to a mismatched VIN number, so more than likely you will need your ECM reprogrammed with the proper VIN. This will need to be taken to the Dodge Dealership to be fixed.

I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

Chevrolet OBD Fault Codes
DTC P1680 - Driver 5 (ECU malfunction)

This is any internal ECU problem (ECU = ECM = PCM device); check other details HERE; keep in mind that its possible that you have to reprogramm the ECU.

Here is a bulletin for this problem.Subject: Service Engine Soon Light On, P1680 (Reprogram or Replace PCM)

Models:
2004 Buick Rainier
2004 Chevrolet Trailblazer
2004 GMC Envoy
2004 Oldsmobile Bravada with 4.2L Engine (VIN S - RPO LL8)

Some customers may comment on the Service Engine Soon Light coming on. Upon investigation, the technician may find a P1680 diagnostic trouble code Check the resistance of the accelerator pedal position sensors using the procedure in the appropriate Service Information for DTC P1680.

If the resistance of the accelerator pedal position sensor is within the specifications shown in the Service Information and the vehicle was built prior to the following VIN breakpoints, then reprogram the PCM with the latest calibration.

If the resistance of the accelerator pedal position sensor is within the specifications shown in the Service Information and the vehicle was built after the following VIN breakpoints, then replace the PCM. If the resistance of the accelerator pedal position sensor is outside the specifications shown in the Service Information, then continue with the diagnostics for DTC P1680.

VIN Breakpoints
• Vehicles built at Oklahoma City Assembly Plant - 46192755
• Vehicles built at Moraine Assembly Plant - 42315833

Hope this help

You have to reprogramm the ECM. Here is a bulletin for this problem.
Subject:
Service Engine Soon Light On, P1680 (Reprogram or Replace PCM)

Models:
2004 Buick Rainier
2004 Chevrolet Trailblazer
2004 GMC Envoy
2004 Oldsmobile Bravada
with 4.2L Engine (VIN S - RPO LL8)

Some customers may comment on the Service Engine Soon Light coming on. Upon investigation, the technician may find a P1680 diagnostic trouble codeCheck the resistance of the accelerator pedal position sensors using the procedure in the appropriate Service Information for DTC P1680.

If the resistance of the accelerator pedal position sensor is within the specifications shown in the Service Information and the vehicle was built prior to the following VIN breakpoints, then reprogram the PCM with the latest calibration.

If the resistance of the accelerator pedal position sensor is within the specifications shown in the Service Information and the vehicle was built after the following VIN breakpoints, then replace the PCM. If the resistance of the accelerator pedal position sensor is outside the specifications shown in the Service Information, then continue with the diagnostics for DTC P1680.

VIN Breakpoints
• Vehicles built at Oklahoma City Assembly Plant - 46192755
• Vehicles built at Moraine Assembly Plant - 42315833

Hope help with this (remember rated this).