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Replacing ECM on 1999 GMC Sierra

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by Crawdaddy, Jul 22, 2013.

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  1. Crawdaddy

    Crawdaddy Moderator Staff Member Platinum Contributor 1000 Posts 100 Posts

    I'm working on a 1999 GMC Sierra (90s bodystyle) with a 7.4L engine. It hasn't been quite running right so my uncle replaced the ECM. Now, it won't start with the new computer. It's a reman computer from AutoZone that was supposedly programmed based on his VIN number. Is there some sort of computer re-learn or security learn that needs to be done before it'll start? It cranks, but doesn't pop.
  2. TRPLXL2

    TRPLXL2 New Member Platinum Contributor 1000 Posts 100 Posts

    Usually they do a crankcase relearn also, I had to do one with hptuners when I bought my ECM.
  3. Crawdaddy

    Crawdaddy Moderator Staff Member Platinum Contributor 1000 Posts 100 Posts

    How do you perform a crankcase relearn.
  4. redvett

    redvett New Member

    Does it start and stall? Is the security light on? If so its passlock issue.
    The following procedure allows for anyone to reprogram the EVO/Passlock™ module learned data code with any tools, other than the scan tool, when any of the following parts are replaced:
    - The EVO/Passlock™ module
    - The passlock™ sensor
    - The VCM/PCM

    The following is the Auto Learn Procedure:
    1) Insure the ignition key is in the ON position.
    2) Clear all EVO/passlock™ module and VCM/PCM DTCs. Record and refer any VCM/PCM DTCs to:
    - For 5.0/5.7L engines, refer to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 5.0/5.7L
    3) Momentarily rotate the ignition key to the CRANK position (Do NOT start the vehicle), then release it to the RUN position (Do NOT key OFF in the process).
    4) Wait 10 minutes. Observe the SECURITY indicator. Refer to the following list for the appropriate responses:
    - If the passlock™ sensor was replaced the SECURITY indicator will flash for the 10 minutes duration.
    - If the EVO/passlock™ module was replaced, the SECURITY indicator will flash for a few seconds and then remain ON for the remainder of the 10 minutes duration.
    - If the VCM/PCM was replaced with a new programmed VCM/PCM and connected to the vehicle for the first time, the vehicle will start and this procedure may not be necessary.
    - If the replacement VCM/PCM was connected to any vehicle at any other time, even momentarily, the SECURITY indicator will flash for a few seconds and then remain ON for the 10 minutes duration.
    5) The SECURITY indicator will transition from flashing to ON briefly to OFF after 10 minutes if remaining in the ignition ON position.
    6) Turn the ignition switch to the OFF position and wait for 10 seconds.
    Repeat steps 3-6 two more times. The new security code is ready to be communicated among the Passlock sensor, EVO/Passlock module and VCM/PCM.
    7) The new password is learned on the next ignition lock cylinder cycle from OFF to CRANK to ON (start attempt).

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