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Carhelp4u, ASE CERTIFIED TECH
Category: Chevy
Satisfied Customers: 5203
Experience:  ASE CERTIFICATION
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1998 silverado wont start security light on

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i''ve replaced the pcm and now truck won''t start. security light flashes three times on stays on.how can i get past this.
This is a common problem and is normally caused by a faulty passlock sensor. The testing for this problem requires a scan tool with the ability to read body failure codes such the theft system. There is a relearn that you could try to make this vehicle operable. Here is what you can try.
  1. Turn ON the ignition, with the engine OFF.
  2. Attempt to start the engine, then release the key to ON; the vehicle will not start.
  3. Observe the SECURITY telltale; after approximately 10 minutes the telltale will turn OFF.
  4. Turn OFF the ignition, and wait 5 seconds.
  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.

    Important: The vehicle learns the Passlock 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.

  6. Start the engine. The vehicle has now learned the Passlock Sensor Data Code and/or password.
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Customer: replied 8 years ago.
i have tried these steps no luck,thanks.
Ok then you really need to have this truck scanned to see what the exact trouble code is. There is no way around this one. I would figure that the new pcm you have installed is not programmed to the correct vin# XXXXX would be causing this problem. This will be something a dealer will need to do to make your truck operable once again. See upon turning the key the truck is smart enough to check all of the modules to verify that they are programmed with the correct vin#. If they are not, you will run into the trouble you are having.