An expensive mistake
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05-29-2008, 09:29 AM
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An expensive mistake
I posted the following a week or so ago to detail my misadventures with the fickle PCMs of a couple of 2000 Dodge Neons. It has been a learning experience and an expensive one for me because I did not do my homework before I acted. I now have both cars running and my mistake has cost me almost $600. I’m adding one more fact that I just learned and if I help even 1 person avoid the costs and time I’ve incurred then it’s worth it. I'm adding what I just learned to my other revalations that I'm reposting.
Did you know that if you swap computers between a car with the Mopar anti theft/ keyless entry system that the first thing the computer does is communicate with the anti theft module? I certainly didn’t know that. I put a computer from my anti theft equipped ES into my standard SE foolishly trying to troubleshoot a starting problem. The anti theft module in the ES talked to the SE computer while it was in the car so when I put the computer back into the SE it thought it had an anti theft system. When it couldn’t find it, it assumed someone was trying to steal the car and shut down the fuel and ignition systems. This resulted in a non functioning computer that couldn’t be reprogrammed. So I had to buy a new computer. Another painful and expensive lesson learned that I can pass on. I had this all explained to me by an experienced local shot that specializes in Mopar computer problems. I also got the same answer from several mechanics on the Internet so I have no reason to think it’s not true. Makes me yearn for the good old days of carburetors and distributors.
I’m going to post my misadventures as a warning to anybody like myself that doesn’t do their homework before they start diagnosing computer problems. I’m sure this has all been posted before somewhere but a lot of this information I got from talking to people that work with MOPARs. If I’m wrong in anything I say I apologize and I hope someone points it out to me.
First and most important the PCM in any Neon after 2000 cannot simply be swapped for one you get out of a similar car, even the same year. There are 4 numbers on the PCM that must match and then you can swap them but you will have to tow the car to the dealer to have the VIN programmed into the new computer. I didn’t know this and thought I could swap computers between two 2000 Neons. I was lucky and only hosed the computer in one of them.
Second you can hose a car that runs perfectly by taking the computer out and putting it in another car. I thought that was impossible but it’s not. Apparently there are systems in the car that can spike a PCM and if you simply replace it then you wind up with 2 dead computers. My local dealer and a repair shop that specializes in MOPAR computer problems verified this to me.
Third the PCM in a Neon can ‘forget’ if you remove it. I couldn’t understand how this can happen but I’ve been assured it can. It doesn’t always happen but apparently it can. You disconnect the computer and when you hook it back up it’s forgotten the VIN. This is apparently something that happens to OBD2 computers in MOPARs and GMs. If it happens you have to tow the car to the dealer or a shop that has the equipment and have the computer reprogrammed. Again this was verified by my local dealer and a local shop that specializes in MOPAR computers. I still don’t understand how this can happen but occasionally it will. Just disconnecting the battery doesn’t do it but unplugging the PCM can.
I’ve learned this all by very expensive experience. I now know more than I ever wanted to about the PCMs in Neons. I spent an entire day running around looking for a computer before a guy in one of the last junkyards I went to told me about the VIN problem. If you need a new computer order one off of ebay and they’ll program it and ship it to you. Just remember if it died then it’s possible that it was one of the systems in the car that killed it and when you put the new on in you could kill it too. The best thing to do is tow it to the dealer and let them fix it. The only downside to that is they’ll charge you for a new PCM.
Did you know that if you swap computers between a car with the Mopar anti theft/ keyless entry system that the first thing the computer does is communicate with the anti theft module? I certainly didn’t know that. I put a computer from my anti theft equipped ES into my standard SE foolishly trying to troubleshoot a starting problem. The anti theft module in the ES talked to the SE computer while it was in the car so when I put the computer back into the SE it thought it had an anti theft system. When it couldn’t find it, it assumed someone was trying to steal the car and shut down the fuel and ignition systems. This resulted in a non functioning computer that couldn’t be reprogrammed. So I had to buy a new computer. Another painful and expensive lesson learned that I can pass on. I had this all explained to me by an experienced local shot that specializes in Mopar computer problems. I also got the same answer from several mechanics on the Internet so I have no reason to think it’s not true. Makes me yearn for the good old days of carburetors and distributors.
I’m going to post my misadventures as a warning to anybody like myself that doesn’t do their homework before they start diagnosing computer problems. I’m sure this has all been posted before somewhere but a lot of this information I got from talking to people that work with MOPARs. If I’m wrong in anything I say I apologize and I hope someone points it out to me.
First and most important the PCM in any Neon after 2000 cannot simply be swapped for one you get out of a similar car, even the same year. There are 4 numbers on the PCM that must match and then you can swap them but you will have to tow the car to the dealer to have the VIN programmed into the new computer. I didn’t know this and thought I could swap computers between two 2000 Neons. I was lucky and only hosed the computer in one of them.
Second you can hose a car that runs perfectly by taking the computer out and putting it in another car. I thought that was impossible but it’s not. Apparently there are systems in the car that can spike a PCM and if you simply replace it then you wind up with 2 dead computers. My local dealer and a repair shop that specializes in MOPAR computer problems verified this to me.
Third the PCM in a Neon can ‘forget’ if you remove it. I couldn’t understand how this can happen but I’ve been assured it can. It doesn’t always happen but apparently it can. You disconnect the computer and when you hook it back up it’s forgotten the VIN. This is apparently something that happens to OBD2 computers in MOPARs and GMs. If it happens you have to tow the car to the dealer or a shop that has the equipment and have the computer reprogrammed. Again this was verified by my local dealer and a local shop that specializes in MOPAR computers. I still don’t understand how this can happen but occasionally it will. Just disconnecting the battery doesn’t do it but unplugging the PCM can.
I’ve learned this all by very expensive experience. I now know more than I ever wanted to about the PCMs in Neons. I spent an entire day running around looking for a computer before a guy in one of the last junkyards I went to told me about the VIN problem. If you need a new computer order one off of ebay and they’ll program it and ship it to you. Just remember if it died then it’s possible that it was one of the systems in the car that killed it and when you put the new on in you could kill it too. The best thing to do is tow it to the dealer and let them fix it. The only downside to that is they’ll charge you for a new PCM.