hey im trying to remove a PCM on a 1991 oldsmobile tornado. i know its not a cadillac but i figured someones done it before because it is a GM. Its located under the glove box. It almost looks like i have to remove the big black box which im guessing is the heater. It looks like the PCM should just slide out but its not, what do i need to disconnect.

ECM is located between programmer and heater case. Disconnect 3 connectors, mounting bracket and wiggle it out. You may find vac. harness is in the way, if so disconnecting it from programmer may help. ECM has chip that will need to be transferred to new ECM.

alright so i dont have to remove the heater case, by the way what is the difference between the PCM and ECM? and ECU also, are they all the same thing?

PCM - Powertrain Control Module (because it controls trans.also), ECM - Engine Control Module, and ECU - Engine Control Unit are all essentially the same part.

alright, i got the old one out and just bought the new one. it says with the new one that i have to diconnect the negative ternminal before removing the PCM to avoid risk of electrical damage, i didnt do this. am i going to have problems? ill disconnect when i install the new one.

It's always best to disconnect negative cable, before connecting or disconnecting modules. Having out of ignition will minimize risk if you don't. Some body control modules (BCM) can be powered up with just the key in the cylinder even in the "Off" position. The concern is about voltage spikes the could damage computer circuits if battery is connected while module is being serviced.

alright i got the new PCM in now and the car runs great. Thanks for all the helpful advice, id be lost without this forum.