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lcorrell

Bcm Programming?

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Background: I recently purchased a non-running 2003 Chevy Silverado 2500HD 4x4 ext cab with the 6.0 and I've been working to diagnose the problem. I have no signal on the Class 2 serial data line, thus no communication with a code scanner. Following the troubleshooting steps I have isolated the BCM from all other modules on the data line and still have no communication with the BCM. I have checked the wiring for opens, shorts to ground or power, or high resistance and the wiring seems to be fine. So the next step in the troubleshooting procedure is to replace the BCM. GM dealer wants $257 for a new BCM and minimum $90 charge for programming it. Says I have to install the module then bring the truck in to be programmed.

 

Now the questions: If I buy a new BCM through GM and install it, will the truck start and run off the blank un-programmed BCM so I can drive it to the dealer for programming? If that won't work, I can get a used BCM for $75 - will the truck start and run off the used BCM with non-matching VIN (after passlock re-learn)? Can the used BCM then be re-programmed at the dealer to have the proper VIN info and match my truck?

 

Thanks for any help.

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Have you checked to see if the cig. lighter has power. If that fuse is blown, you'll get no communication from the port.

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Yes, I have verified that. All fuses are good. I have ground at DLC pins 4 and 5 and I have positive voltage at pin 16. Scan tool powers up, but does not communicate. I have also already replaced the ignition switch and nuetral safety switch (PNP) and verified good battery and cables/connections.

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So you can't connect with the PCM either? Each device is connected independent of each other. The BCM is not what is preventing it from starting.

Edited by Jennabear

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So you can't connect with the PCM either? Each device is connected independent of each other. The BCM is not what is preventing it from starting.

 

I'm just following the diagnostic procedure in my repair manual. It says the bcm is the Power Mode Master (PMM) and controls all other modules including the pcm (on my truck anyway). The wiring diagrams show there is no direct link between the pcm and the diagnostic link connector, it shows the pcm connects directly to the bcm which then connects to the dlc. The bcm is what receives the ignition switch signal and sends out the signals to all other modules to activate. So if the bcm is dead and sends no signal to anything, the truck would not start. Which means the bcm is what is preventing my truck from starting - according to my repair manual.

 

Believe me, I've been all over this truck checking things and testing. At this point my next step is to replace the bcm. But, I need to know about programming the replacement bcm as I asked above to know what to expect.

I have three possible scenarios:

1)I buy a new replacement bcm from my gm dealer, install it, start the truck and drive it to the dealer for programming.

2)I buy a new replacement bcm from my gm dealer, install it, the truck won't start, I have it towed to the dealer for programming.

3)I buy a used replacement bcm from the salvage yard, install it, start the truck and drive it to the dealer for programming.

 

I'm just looking for info from someone who knows for sure which of those scenarios is realistic.

 

Thanks again

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So you can't connect with the PCM either? Each device is connected independent of each other. The BCM is not what is preventing it from starting.

 

I'm just following the diagnostic procedure in my repair manual. It says the bcm is the Power Mode Master (PMM) and controls all other modules including the pcm (on my truck anyway).

I think your manual is for a newer vehicle, power mode mastering was not used on chevy trucks till 05-06.

The wiring diagrams show there is no direct link between the pcm and the diagnostic link connector, it shows the pcm connects directly to the bcm which then connects to the dlc.

That is the second clue that the manual is wrong. The diagram should show the bcm and pcm in a loop to a splice pack then to the dlc. The way your truck should be wired is that the bcm and pcm are wired togeather then they have independant circuits back to the dlc so that either module can communicate with the scan tool independant of the other.

The bcm is what receives the ignition switch signal and sends out the signals to all other modules to activate. So if the bcm is dead and sends no signal to anything, the truck would not start. Which means the bcm is what is preventing my truck from starting - according to my repair manual.

Again on an 07 this would be true but not on an 03. The truck will not start without the bcm because of the security but it does not send out the on signal for the other modules like a new one would.

 

Believe me, I've been all over this truck checking things and testing. At this point my next step is to replace the bcm. But, I need to know about programming the replacement bcm as I asked above to know what to expect.

I have three possible scenarios: All that said if you still want to go with the bcm I'll tell you what I know. You could get lucky and need the bcm but I wouldn't put money on it (which you are).

1)I buy a new replacement bcm from my gm dealer, install it, start the truck and drive it to the dealer for programming.

 

You could do this, you will have to program the security code first. Then drive it in to have the RPO's programmed in the BCM.

 

 

  1. 1 Turn ON the ignition, with the engine OFF.

     

 

  1. 2 Attempt to start the engine, then release the key to ON; the vehicle will not start.

     

 

  1. 3 Observe the SECURITY telltale; after approximately 10 minutes the telltale will turn OFF.

     

 

  1. 4 Turn OFF the ignition, and wait 5 seconds.

     

 

  1. 5 Repeat steps 1 through 4 two more times for a total of 3 cycles/30 minutes; the vehicle is now ready to relearn the Passlock Sensor Data Code and/or passwords on the next ignition switch transition from OFF to CRANK.

     

 

  1. Important: The vehicle learns the Passlock Sensor Data Code and/or password on the next ignition switch transition from OFF to CRANK. You must turn the ignition OFF before attempting to start the vehicle.

     

    Start the engine. The vehicle has now learned the Passlock Sensor Data Code and/or password.

     

With a scan tool, clear any DTCs, if needed. History DTCs will self clear after 100 ignition cycles.

 

2)I buy a new replacement bcm from my gm dealer, install it, the truck won't start, I have it towed to the dealer for programming.

Follow the above and you should be able to drive it in.

3)I buy a used replacement bcm from the salvage yard, install it, start the truck and drive it to the dealer for programming.

You can try this and try the above but I wouldn't know if it would work or not. All year, make and model bcm's are a little different and without trying this on your particular make and model. If you can get the security to work the RPO's might not be able to be programmed, it's really just trial and error with this method.

 

I'm just looking for info from someone who knows for sure which of those scenarios is realistic.

 

Thanks again

Edited by sparkstech

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I have the same problem with my 2002 LTZ Trail Blazer. My mother has a 2002 LS I took her BCM out and put it in my 2002 LTZ and did the key learn and my2002 LTZ started right on up. So I went to the junk yard and got a BCM from a newer TrailBlazer did the learn key and it started. I let it run for about six minutes and it stopped. I tried to put my mother's BCM back in and it will not start. I think I burned something out. Any help would be appericated

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I have the same problem with my 2002 LTZ Trail Blazer. My mother has a 2002 LS I took her BCM out and put it in my 2002 LTZ and did the key learn and my2002 LTZ started right on up. So I went to the junk yard and got a BCM from a newer TrailBlazer did the learn key and it started. I let it run for about six minutes and it stopped. I tried to put my mother's BCM back in and it will not start. I think I burned something out. Any help would be appericated

 

 

I suggest that you open a new thread and ask your question rather than hijacking this one... OP is looking for help for his problem, not yours...

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What sense would that make to start a new thread if we have the same problem? Maybe he can help me by sharing his experience with this problem. No hijacking intended. If you cannot help shut up!

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Kindly don't tell people to shut up. It kinda rubs people the wrong way sometimes......You've made me decide to leave this thread without helping you. G'bye. :(

 

BTW, the OP hasn't been here since August 24th, 2010. So doubt he'll be any help

Edited by txab

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the op wont help u as this thread was over in Aug,

 

take it to the dealer,no one will help u now ,,,bye bye

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Well he got under my skin accusing me of hijacking a thread. If he could not or would not help then he should keep his negative comments to him self. My intent was to seek help nothing more! From the response I see a few of you take exception with me telling him to shut up, well you few can shut up also. OK, so you will not help, fine, in all probability you could not. The information on the thread was a big help anyway.

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No I do not have it figured out yet, but I do have a pretty good idea what to check. Beside you are not going to help anyway.

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What sense would that make to start a new thread if we have the same problem? Maybe he can help me by sharing his experience with this problem. No hijacking intended. If you cannot help shut up!

 

 

I suggested that you start a new thread since a 2002 Trail Blazer is not a 2003 Silverado and the problem is not the same and so on. I see by your attitude that you got all the help you need. I have a Haynes manual that you can have if it will help.

 

btw, your problem is not the same as the original poster, his is fixed, yours is not!

Edited by Hawkeye-08

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Your are correct! Not the same Vehicle, but the same principles. I do not have an attitude, but I will not allow anyone to chastise me in a degrading tone for something so trivial. This is all I will have to say about this. If members thing I have an attitude or have done something wrong then do not bother to reply I have heard enough. I get the picture. Those that want to help thank you. Maybe I should have started my own thread but his problem was so much like mine and I asked a question. Do not mean for this to get out of hand with a few members.

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First, let me appologize for not coming back an updating my topic! I hate when I find topics that could contain the exact info I need only to find that the topic was never updated with the resolution.

 

The key to me figure out my issue was that the position of the shift lever changed the behaviour of my problem. I don't remember how I figured that out, but it turned out to be very important info. I started tracing the wiring diagrams in my repair manual. I focused on the shift position switch that's mounted on the side of the transmission. I individually checked each wire against the repair manual for ground, power, etc. I found that the ground wire to the switch did not have ground. Traced that to a broken ground connection on the rear of the passenger side cylinder head. Apparently the ecm, bcm, or something along those lines used this same grounding point and due to the lack of ground they were backfeeding through other circuits. Fixed that ground point and everything was fine!

 

So, I never really did find out about the BCM programming issue since I didn't have to replace mine. I think it's rediculous that I'd be at the mercy of GM to program a part - that makes it impossible for me to work on and repair my own vehicle - I think that's illegal or something!

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