Pontiac Repair: 2001 grand prix ecm, upper intake manifold, coolant temp

Question
We have determined that the ecm in my 2001 Pontiac Grand Prix (3.8 engine) is bad. It will not give codes to tell us what caused the ecm to fail. We have a new one to install, but we are aware it too will fail unless we find out what caused the old one to fail. Is there a chart that tells us what the pin resistance should be on each of the pins and how to decifer the code? Or is there a way to get the codes from the old ecm that is not reading? I know that we uses to do the "key" test to get codes, but honestly its been so long I have forgotten how. Will that give the codes we need since it doesn't throw codes when we hook it up for diagnostics? The fans on the cooling system do not come on, causing the car to overheat very quickly...then the car does not shift properly. I have to replace water a couple times a week, but cannot find any leaks. There is no water in the oil, but the coolant seems to disappear. We are perplexed. The car runs rough, overheats and shifts badly...can't afford a new one...Help!

Answer
Hi Linda:

the new cars like this one will not flash out codes like the older cars that went away in 1996. So it may not have a bad computer. the fans not going on my not bee a computre issue it could be a lot of other things like a blown fan fuse to a bad wire or connection in any of the fan control ckts. A bad coolant temp sensor could cause it as well. I do not have a chart for pin out for the ckts. If you do find a wire diagarm for this car any of the solenoids the computer controls being either in the transmission or for the engine none of the solenoids or valves should have less then 25 ohms of resistance. If any do that could be one of your issues. Did you have the car scanned for codes at one of the big box auto parts stores? As fars as the coolant chances are the upper intake manifold is bad and it's sucking coolant into the combustion chanbers and burning it off. if you over heated it bad enough it may need head gaskets :( !  good luck :-}