04 Grand Am No Start, PCM, BCM?

NickD

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"The PCM verifies that all parameter are met for starting." Would be nice if listed those parameters, know on some cars, have to step on the brake pedal first before it would crank, could be a dirty brake switch if that is the case.

"The PG-260D is a non-repairable starter motor." Actually it is rebuildable if not completely rusted through. The special tool you need to open it, is a can opener. I have opened solenoids by putting them in my machine lath and using a blunt nose tool to unroll the rim. GM has developed a strong allergy to screws.
 

JAZAuto

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Thanks Nick and Jim for the comments and the diagrams! On the Theft Deterrent schematic there is a rectangle that says "DLC Schematic" (I think) and it ties together PCM serial data, Theft Module, and the Instrument Panel Cluster. This seems to tie all my symptoms together so far. Do you think this will provide further clues or is the problem just one of the units that I just mentioned? Really, if I can fix whatever is inhibiting the PCM serial data at the diagonostic connector (no response from code reader) I believe the car will be running!
 

NickD

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These things do use flashram to store the OS just like in your digital camera. Possible you need to have your ram reflashed with the program, need a laptop, GMTech II scanner and the firmware you can't get or at least don't want to pay the price for it. My dealer wants 80 bucks to do it just as a matter of reference, only takes about ten minutes, but that equipment is extremely expensive to do a reflash. Could check for corroded pins first.

It's just like your home computer, when you have problems, first thing you check is your software.
 

Gus

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Takes more than 10 minutes Nick......I have to go get your vehicle...then I have to hook up a special battery charger.....then I have to hook up your car to our central computer.....and as I'm loading the specifics of your vehicle, some times it asks me if your car has a certain option....now I have to do a VIN check and check your options.....I may even have to pull some fuses before doing the download......then I do the download....after that, I may have to do a crankshaft variation relearn.....then I have to check the vehicle to see if the reflash took care of the problem.....no such thing as 10 minutes....

As for this vehicle, it's a simple job if you can read the BCM and PCM data....if you can't then you don't know if the BCM is sending the correct message to the PCM to ground the starter relay....
 

NickD

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Okay, in my case, just an upgrade, dealer new I was coming, firmware already downloaded into his laptop, and he already had my VIN, so I didn't count those time, hit the starter, engine started, said I was good to go.

But do you agree it's possible that his firmware is corrupted?
 

JAZAuto

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FINAL RESULT: Car fixed by dealer. Installed new ignition switch (don't think it really was bad but OK) and reflashed the BCM firmware. Cost:$350. Thanks Nick and Gus for the input on this. Perhaps intermittent contacts on the switch caused the BCM computer go crazy - who knows. But the car is fixed. Joe
 

NickD

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Good to hear, it's problems with the microprocessor receiving a jagged voltage when the key is first turned on. Has to be a sharp rise in 12 volts that is stepped down to five volts by a voltage regulator. This same jagged voltage is applied to the Vss pin of the processor that powers it so the processor is not really turned on. And this same voltage is applied through a resistor tied to the POR pin or the power on reset pin to a capacitor tied to ground. In theory, this voltage is zero volts or less than 1.2 volts at the POR pin that pulls it low to reset the processor that sets the program counter in the processor to a zero count state that starts the program from zero, the starting point. With a jagged voltage, that capacitor starts to charge, but the microprossor isn't really on at this point. So some ragged numbers appears to start the program from the wrong point. In other words, a mess.

I had to clean several ignition switch contacts, use a jewelers buffing wheel to a high mirror finish that solves this problem and keeps the same ignition key that came with the vehicle. You can see this on an oscilloscope by watching both Vss and the POR pin, POR pin never goes low. Other problems between Vss and the positive post of the battery are in connectors and fuse holders. All recently ignition switch contacts I have seen are made from bare copper due to EPA regulations regarding plating, turn green which is copper oxide, an excellent insulators and the grease also turns rock hard. But is a wiping action switch that does help to keep the contacts clean.

Seen cars where the volume control wouldn't work due to a lack of a good POR, another digital monster that depends upon a sharp clean rise in voltage. Time to clean the switch, that's not too bad, but removing some can really be a pain.
 

Gus

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Was it the Passlock module and lock cylinder that was replaced or the ignition switch? Two different animals....
 

JAZAuto

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You're right Gus, it was the lock cylinder that was actually replaced. I don't have the full paperwork from the GM dealership that ended up doing the job. I will try to get it for my own education. Thanks again for the input. JAZ
 

Gus

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Then it was the lock cylinder/PassLock module(the usual culprit), not the the ignition switch......
 

hoodjuggz

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i was gonna say with the replacement parts a mild corrosion on contacts will have the ad converter give the computer a weird pattern. im glad its fixed for you. instead of seeing 1010101100 the computer was seeing 1010DER010011001. :eek: sorry i didnt see your post earlyer my brother in law has the same car and had the same issue.
 

JAZAuto

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Thanks for the comments above. Yes, the 04 Grand Am on this thread was fixed by re-keying with a new cylinder assembly and then reprgramming the BCM. Is this a correct statement that the key cylinder/Passlock module is a three terminal device that communicates with the BCM to basically "boot up" the car when the key is turned and thus enables the main PCM to allow the car to start and run?
 

alexandjojo

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Say jaz, I am glad you posted this because I am going through the same stuff with a Buick century and drove me nuts.
 

NickD

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Could be in for the same problem with my 04 Cavalier, never paid much attention to it, but see I would have 40 some odd pages to read in the shop manual. It's purpose is to prevent someone from stealing your car that can be done by attempting to force the ignition switch without the key in it. Doesn't say how much force, a gram-centimeter? And would the same thing happen if your key was not fully inserted? Didn't find a circuit of it, but probably wouldn't do much good if I did as the passlock sensor, ignition cylinder, BCM, and PCM, plus the data links are all involved. Just kind of telling me to be easy with the key. Yep, you need a GM Tech II scanner for any kind of troubleshooting.

Not sure why anybody would want to steal my car, last year was at my Chevy dealer and he tried to sell me a new Cobalt, with my car in perfect condition and only 45K miles on it at the time, he only offered 1,500 bucks for it. Could only reply, why in the hell am I paying for collision and comprehensive insurance on this thing? Can see why they put these things for new cars on the lot, but should disable them as soon as you buy one and drive off the lot, your car at that point is worthless.

One of the possible causes is a corrupt password in either the BCM or PCM, on one hand they claim the password is protected in case the battery goes dead, on the other hand, they give long steps with the scanner on how to reprogram it. Any electrical surge can also cause this problem, typical of flashram in general.

Seems like on this board, any form of anti-thief has kept the legitimate owner from starting his vehicle, but just wonder who would want to steal a GM vehicle?
 

alexandjojo

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I just have a question.....Once the ignition lock key/cylinder is replace is there communication with the scanner?
 
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