Rick's Free Auto Repair Advice

Security light on — GM vehicle

If you own a GM vehicle and have a security light on, read this article and the associated posts

This is one in a series of articles. READ THIS FIRST

GM made several different types of anti-theft systems. VATS, PassKey, and PassLock. The troubleshoot and reset procedures are different for each. PassLock seems to have the highest failure rate. So if you have a key WITHOUT a chip in it, chances are it’s a PassLock system. This article describes how to troublshoot and fix a PassLock system. But here are some more articles to help

Click here to see the resetting procedure for PassLock

Click here to see the trouble codes for a PassLock system

Click here to see a typical PassLock wiring diagram

IF you have a PassKEY system, click here to see the reset procedure

If you swap out a PCM in a late ‘90’s GM vehicle and encounter an anti-theft light, you may not have to take it to the dealer for reprogramming. The PCM is set up to recognize a certain pattern as it relearns the key code. You can duplicate the pattern by performing this sequence exactly:

1) Hook up a battery charger and set at low rate of charge.
2) Turn the key to crank the engine just long enough to engage the starter.
3) Leave the key in that position for at least 10 minutes. (Some shops say it takes as long as 30 mins).
4) When the theft light turns off, turn the key to OFF for 5 seconds and then back to start and leave key in that position for 10 minutes.
5) When the theft light turns off a second time, the PCM has learned the new key code and you can start the engine.

© 2012 Rick Muscoplat

Posted on by Rick Muscoplat


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