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GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29585
Experience:  GM Grand Master Technician 2007. 14 years experience.
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2003 chevy Impala replaced bcm to cure problems with warning

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2003 chevy Impala replaced bcm to cure problems with warning lights and door locks an A/C. Still have problems starting now and then. Will not turn over at all. I understand the passlock system cuts fuel when it does not recognize the key but my car will not turn over. SAometimes works fine. No warning lights or engine codes.
Welcome. Did you relearn the passlock system or do any programming on this unit?
Customer: replied 8 years ago.

I took the new bcm to the dealer to have it installed and programed. Car started when I left and again later but then did not start when tried and hour later.


OK, try the relearn again.

  • Turn ON the ignition, with the engine OFF.
  • Attempt to start the engine, then release the key to ON (vehicle will not start).
  • Observe the SECURITY telltale, after approximately 10 minutes the telltale will turn OFF.
  • Turn OFF the ignition, and wait 5 seconds.
  • Repeat steps 1 through 4 two more times for a total of 3 cycles/30 minutes (the vehicle is now ready to relearn the PasslockTM Sensor Data Code and/or passwords on the next ignition switch transition from OFF to CRANK).

    Important: The vehicle learns the PasslockTM Sensor Data Code and/or password XXXXX 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 PasslockTM Sensor Data Code and/or password).
  • Customer: replied 8 years ago.
    Everything I have read in the manual and on-line does not say about stopping the car from cranking. Is this part of the passlock system. Also if this does not work then what do I do, or can the passlock system be by-passed?

    The system will prevent the engine from cranking. I suggest we try this first.

    Customer: replied 8 years ago.
    ok I will try this but if it does not work how do I get in touch with you?
    You can simply reply. I need to go out for about 30 mins so I will check in then.
    Customer: replied 8 years ago.
    I did as you said and followed the relearn process you said to the letter. The car did not crank at all.
    Ok, what does the security light do? WHat does the check engine light do?
    Customer: replied 8 years ago.

    security light telltale went out after the first ten mins as you said but after relearn all I get is the security warning on dash and battery symbol cause it will not crank. engine symbol is also lit

    I am thinking there is a problem with the setup or even your new BCM. Was this BCM new or used?
    Customer: replied 8 years ago.
    It was new and problem was happening even before bcm change. Intermittent starting and other problems. Now just intermittent starting
    Hmmmm, what diagnosis was done leading up to the BCM replacement?
    Customer: replied 8 years ago.
    only codes were for cooling fan 1 & 2 which was an unrelated problem. Bad cooling fan motor. BCM was changed for misc. messages like battery and service soon and A/C not comming on and radio locked out and door locks locking and unlocking over and over till fuse blows. also interior lights working and not working also odometer back light sometimes on and sometimes off. All cured by bcm replacement. By the way radio is not locked out now at all.
    OK, Take both battery cables off , touch the ends together for 10 seconds, than attach them to the battery and see what happens.
    Customer: replied 8 years ago.
    What am I looking to happen? This will not damage anything?
    Nothing but a complete system reset. No sparks, nothing but a small spark when you connect the battery, but that is normal.
    Customer: replied 8 years ago.

    ok should I try to start after this or come back here?


    Try to start after.
    Customer: replied 8 years ago.
    I did as you said with the battery cables. Nothing is any different. When I try to start nothing happens. In the on position the radio plays and the driving lights are on and interior lights are on. On the dash all lights are on as normal and also have the little engine symbol lit and the messages -- security , door ajar ( of course door is open) and battery symbol. I am really stumped. prior to changing the BCM the radio was locked and the lights on dash and driving lights did not act normal. Also doors did not lock when going to drive and unlock when return to park. All this works fine now.

    OK, lets try something different. Using a test light see if there is power on the small stud at the starter when the key is in start.

    Customer: replied 8 years ago.
    I checked this afternoon and the answer is no. I am an electronics tech on household equip but not cars. I aslo jumped the starter solenoid and the car started but shut right off. Again as if the security system had sut the fuel off.

    Ok, does the starter relay in the underhood fuse block click when you try to start?

    Customer: replied 8 years ago.
    not sure but I do not think so I can go check if you need

    Please check.

    Customer: replied 8 years ago.
    Going from off to on position I feel the ignition relay click. When go to start position the crank relay does not click. Also in the start position the radio and driving lights and dash lights go out.
    Ok, next under the dash locate the yellow wire from the start switch and see if there is power there in start.
    Customer: replied 8 years ago.

    yellow wire going from ignition switch to BCM?

    It goes to the underhood fuse block, but that does not matter where it goes, we simply need to know if there is power on that in start.
    Customer: replied 8 years ago.

    when I turn key to start position there is power on that wire


    OK, Does anything happen in neutral when you try to start?

    We are almost near the end of what we can check with out a scan tool.

    Customer: replied 8 years ago.
    I tried in neutral and nothing. No codes when checked with a scan tool. Does it sound to you like the security system has it locked out ot the passlock as they call it? I am at my wits end and afraid the dealer will not have much luck but just try and experiment.
    I am starting to think your replacement BCM is the issue. The BCM And PCM talk to take care of security. Your scan tool, is it a code reader only?
    Customer: replied 8 years ago.
    yes code only
    Ok, boy I don't want to tell you to go back to the dealer, but with out a scan tool to see what is being transmitted, we are now going to chase our tails.
    Customer: replied 8 years ago.
    It started fine after the BCM change and again later. but went for a drive and did not start again right away but did start eventually. Now today nothing.

    What is happening is the computer is not commanding the starter relay to engage. You are getting power from the switch on the yellow. The yellow goes to the PCM, not the fuse block. Below is a schematic.

    Object Number: 652717  Size: FS

    Object Number: 798566  Size: FS


    Customer: replied 8 years ago.

    but even when I jumped the starter and the engine started, it quit right away like the security system had cut the fuel


    THat is because the fuel was cut. The security controls the starter and fuel on these.
    Customer: replied 8 years ago.
    what do you suggest I do now. I do not want to get ripped off on a repair.

    I would get a diagnostic done. We are at the end of what we can test.

    HERE is the no start diagnosis.


    Customer: replied 8 years ago.
    what should I get charged at the dealer for a estimate or this diagnosis.
    I would suspect a proper diagnosis will be 1 hour or less so between 75 and 100. Do you have warranty on the BCM that you bought?
    Customer: replied 8 years ago.
    yes I have a one year replacement if bad
    OK, best case you spend the diagnosis cost.
    Customer: replied 8 years ago.

    ok sounds like I need to get it in to the dealer. Hopefully I can get it started. I have had luck unplugging the plugs on the BCM and replugging and then it starts.

    wish you were the one working on it for me.

    So do I!!!
    Customer: replied 8 years ago.

    Thank-you for all your help and I wish I could get back to you with the result. With your next reply I will accept your answer because Sir you earned your money and more


    You may reply at any time to this post. I would appreciate your posting the results.
    Customer: replied 8 years ago.
    I can reply to it even after I accept and we close it out?
    Yes, you can always reply to this post.
    GM Tech (Cam) and 4 other Chevy Specialists are ready to help you
    Customer: replied 8 years ago.

    Thank you Sir for your help this far and I will accept when you say good night. It has been good to know you and your expertise is greatly appreciated.


    Thank you and Good Night

    Thank you as well. Have a great evening and good luck.