A used PCM in a 2004 Trailblazer?

[wallus]

We tried a used PCM in a 2004 Trailblazer 4.2 4x4 today because we couldn't find the cause for multiple codes and fuel gauge pegged at full. Guess what? The codes went away and the fuel gauge works. Darned if it won't crank though.
Has anyone success with a used PCM? Any idea why it won't crank? It cranks and runs with the old PCM but has no throttle response, multiple codes and the fuel gauge reads full (it's only got quarter tank)
We did find the dark blue wire pulled out at the fan clutch connector and repaired that but it didn't change anything. I'm more curious though about a successful used PCM swap though. Thanks to all, Wally

 

[The_Roadie]

People do it all the time when getting a PCMofNC tune.

What was the source of your used one? Guaranteed working, or unknown junkyard dog?

 

[MAY03LT]

With the new (to you) pcm in, if you turn the key to run does the security light flash?

 

[kickass audio]

You guaranteed need to do a security and CASE relearn. The security relearn you can try doing at home however you may fail at doing so as I believe the VIN is learned on them but I may be wrong with that. Here is a vid from May03 about the pcm swap: https://www.youtube.com/watch?v=yg1zcIfkUJY

Again don't think that a security relearn will get it working, and if it does you got lucky but still need a buddy with a high end scan tool or a shop perform that CASE relearn.

 

[wallus]

People do it all the time when getting a PCMofNC tune.

What was the source of your used one? Guaranteed working, or unknown junkyard dog?

An unknown junkyard dog is what it was. We just tried it to give us some ideas. Would a security or CASE problem cause a no crank or just a no start?

 

[Wooluf1952]

The security will cause a no crank situation.

 

[wallus]

The security will cause a no crank situation.

So I assume the PCM is looking for the key from the junkyard vehicle?

 

[kickass audio]

Its not the key that its looking for. It is communicating with your BCM and other components on your truck to see what the VIN numbers all are and if it doesn't match up it stops it. Did you try the security relearn like may03 did in the video in an attempt to get it to crank? Plus you didn't answer his one question on if you start it does the security light flash in the dash? We need more info to help you bro.

 

[wallus]

04 Trailblazer 4.2 L 4x4
Thanks for all your help guys. The used PCM from the wrecking yard accepted the relearn after three tries. It fired up and road tested with only one minor problem . It has a slight surge under heavy throttle. We're going to send the guy to our favorite "Stealer" to have the CASE relearn done to see if that fixes it. If he does take it I will report back to you. Thanks again, Wally