Can I replace Saturn S-series PCM without VIN programming?

I have a 2000 Saturn SL with manual tranny that started reporting EGR valve issue P1404. I traced fault to missing 12V at EGR valve from PCM. Wiring between PCM and EGR OK, no opens or ground faults. I ordered a salvage-yard PCM of exact same part number and type as original unit; it arrived and looks identical to existing faulty PCM, same part number. I did this because I assumed it would be plug-and-play, no need for dealer to program car VIN number into replacement PCM. I installed it and observed 12V to EGR valve now present; primary problem solved. But new problem #2 is now car won't start, it cranks but will not start. Also fuel gauge doesn't move off 'E' even though tank has 1/2 tank of gas. I reinstalled 'faulty' PCM and engine starts fine and fuel gauge reads 1/2 of gas. I contacted salvage yard and they say I need to take PCM to dealer and have them program in car VIN, allegedly because PCM is unable to communicate with other car components such as IP cluster. This sounds contrary to what little I've read about this type of PCM. I had understood that VIN didn't matter. It would mean other items like Instrument Panel cluster, if replaced, also require reprogramming with VIN. If replacement PCM requires reprogramming with existing VIN then what is PCM communicating with that is checking for legacy VIN? BTW, this car is no frills, manual transmission, no security, manual windows, no key fobs, probably most basic, least expensive car they produced.

 

My experience up to this point is that answer is PCM requires programming with VIN. Why? Because PCM communicates with BCM and both programmed with VIN. I observed this when I replaced unprogrammed PCM. Scan tool showed VIN had not changed from legacy number with new, unprogrammed PCM installed and odometer still reflected legacy mileage which I think both were coming from BCM. Also while fuel gauge was displaying correct level with new, unprogrammed PCM the car would not start. It was like the fuel injectors weren't working.

 

You need to do a pass lock II relearn procedure to marry the PCM to the BCM.

Surfing the net for the instructions and follow them to the letter. Meaning if it does not say to remove the key from the ignition, don't do it. Leave it in there. Hook your battery up to a charger as this is a 30 minute procedure. I don't think a 10-minute procedure will work when marrying a PCM and BCM. Alternatively, hook your battery up jumpstyle to a running vehicle's battery.

The new PCM is not talking properly with the existing BCM. I don't actually know what information they are handshaking with. But the PCM must receive what it expects from the BCM in order to enable the fuel injectors. The default state for a pass lock II enabled Saturn is "injectors inhibited".

Only when the passlock ignition sensor, BCM, and PCM are all properly married and communicating with each other will the vehicle disinhibit the injectors allowing fuel to the engine and the engine to start.

The other issue you will run into is that indeed each PCM and BCM are VIN programmed. However, what matters when buying salvage yard PCMs and bcms is what vehicle it came out of.

Saturn may have used PCM part number 228133 in both SL1 manuals and automatics. If you put the PCM from an automatic into a manual, it may run the engine but will be forever looking for the auto trans and throwing SES codes till the end of time.

More problematic is trying to find a suitable BCM. It controls almost all of the non-engine related functionality in the vehicle. This is where the vin programming is most important. The VIN is tied to the option list and what is installed in the actual vehicle as built. It is shall we say customized to the exact vehicle. If you buy a used BCM, again you really need to know what vehicle it came out of and on top of that, what options vehicle had. If it's close enough to identical to your vehicle, you can probably get by if you can handle a few things not working because the donor BCM was in a car that didn't have them. Otherwise you need to get a refurbished BCM and just have it programmed to match your VIN so everything works.

 

Thanks for the reply, great information. I did get a programmed PCM that works great and resolved my EGR problem so I'll keep this information in my back-pocket in case this question ever comes up again in the future.