2001 3.5 Trouble Starting

My 2001 3.5 with about 200K miles on it is suddenly difficult to start and my entire dash freaks out intermittently. All warning lights come on and I'm also getting error messages where there should be numbers like the odometer reading etc. I thought the starting problem was just a bad starter but I had a GM dealer diagnose the problem and they tell me it's a problem with the main engine, the Body control and the abs computer units not communicating properly or going off and on. The car does eventually start and drive so the problem is intermittent and getting worse. Of course, it's too much money for a dealer to fix so I'm thinking of swapping these units out myself provided it's feasible. I'd appreciate any help in locating the affected units. Where is the main engine computer, the body control computer and the ABS computer located on the 2001 3.5 Aurora?

Protek22

These units are not plug and play units.....they have to be programmed specifically to the car.....I am not sure of the year this happened, but some units are programmed to the vehicle's VIN number, so you can't just take one out of another vehicle and put it in yours....if you try to, when the modules start to communicate with one another, and they don't see the same VIN in the module, they set communication codes and in some cases don't function....

Fortunately, I had sense enough to doubt the dealer's diagnosis and refrained from going out and buying computer units. I always thought it was just a bad starter so I took some time to examine the 2001 Aurora's starter wiring and function to see exactly what part the computer plays in it. I found that the only thing the PCM does with the starter is energize the starter relay if the transmission is in park or neutral. This confirmed that the computer issues I was having were a completely separate issue and had nothing to do with my starting problem. Since the dealer's diagnosis was clearly nonsense. I replaced the starter myself and voila, starting problem fixed! As for the computer problems I was having, they vanished too when the system was down for 24 hrs and reset after the starter repair. These issues were apparently due to faults in the BCM rather than the PCM or ABS unit.