I was told that an ECM will rarely go bad on its own and that there is usually a outside cause( a short in the wiring, a voltage spike etc. etc.) Is this true? when replacing the ECM is it neccesary to replace the prom also? Or is it moved to the new ECM from the old one? Do they go bad? My second question is a rather easy one, is the ECM located behind the glovebox or behind the passinger kick panel on a 91 bonneville. I'm haveing some real issues with the car and as you can tell I'm in no way a mechanic. As a matter of fact I just bought my first set of tools lol. I have put them to use though. Replaced the ignition modual, the 3 coil packs,the O2 sensor, the cam sensor, the maf sensor, and gave it new plugs and wires. I won't go into the cars problems untill I get updated post codes so I don't waste your valuable time. Thank you in advance!

The potential for them to go bad on their own. There'* no great mystery inside the box, it'* just a bunch of IC'* on a circuit board. While a modern TV is more complicated, it'* just as prone to failure.


<snip>when replacing the ECM is it neccesary to replace the prom also?<snip>

No, you can (and should) transfer the calibrator prom from the old PCM to the new one. However, Proms can go bad too (they also have the knock sensor logic built in on a piggy-backed circuit board inside the plastic housing) The calibrator will have a 4 character code on it... something lke "ASSK"...the 4 character code is the broadcast ID that identifies the software version on the chip and what specialized code your car needs. If you have to replace the calibrator, it should be with one with the same code, or a replacement with a higher revision of the same software.

<snip..>I'm haveing some real issues with the car and as you can tell I'm in no way a mechanic.<snip..>

No problem, the ECM is easy to replace, and getting a used one from a junk yard is probably the first purchase to make (they are pretty cheap..handy to have a spare that you can test with.) If the car is running and throwing codes, then the ECM may be OK. You got to do some digging to trace down the problem.