My 94 4.3 type w recently started to show code 42. I've done a lot of work on the truck and this was the first time it showed that code. I've replaced plugs, wires, coil, MAP, TPS, alternator, EGR, PCV, IAC, and the list of parts goes on. I've been rebuilding this truck for about 18 months.

I replaced the ECM and reused the PROM. After installing it I still had code 42. I was already planning on replacing the distributor so I took it up and had that done. I asked them to try to find the cause of the 42. After several days a new distributor the truck runs much better but not quite right. They did not resolve the code. Their suggestion was that it is either a faulty ECM or a wiring issue.

So my questions are 1) How likely is it that a new BSE brand ECM from Autozone would be defective out of the box? and 2) If it's not the ECM could it be caused by another sensor? and 3) Is there a common wiring problem to look for? (maybe a particular part of the harness that is prone to damage due to design?)

I'm not above pulling the dash apart if I have to so I can chase the wires but I wanted to see if anyone else had a similar problem and hopefully feel a little less like I'm just blindly searching for something.

 

Maybe this will help:

https://batauto.com/threads/g-m-%E2%...code-42.14056/


George