General Motors Passlock Security System

Is the security light flashing in your GM vehicle (Chevrolet, Pontiac, Cadillac, Oldsmobile, Saturn, or GMC)? Is this keeping your car from starting? Let me guess, it cranks and as soon as it starts – it just does? This is a very common problem on many General Motors vehicles, due to inherit design flaws in the VATS (vehicle anti-theft system) – Passkey and Passlock I and II systems. There are a handful of potential causes and, fortunately, fixes.

If you’re lucky, you can reprogram it with a learning procedure. This works by retraining the system as to what the correct key resistance value should be. It doesn’t matter whether you have a resistor in your key or if it’s embedded in the ignition switch. The process is fairly straightforward and simple and takes about 30 minutes.

For many, the reprogram won’t work or it works but only for a little while. This is usually due to a faulty ignition switch or BCM (body control module). More often than not, replacing the ignition switch and reprogramming / relearning the key again will fix it. Some report that they have to replace the switch every 4-5 years and that it gets expensive. The BCM is very expensive, and can only be had at the dealer. It’s usually a last resort. The dealership can test your system but it usually costs $85 dollars or more.

The security system can also fail because of old, corroded, or poorly connected wiring. Since the BCM usually relies on a resistance value from the ignition switch, corrosion on the connectors (they’re NOT gold plated) or in the wiring can cause the resistance readings to fade over time. Once it fades out of range, it trips the security again.

So, what do you do if you’ve already replaced your ignition switch, BCM, and checked your wiring? Or, what if you don’t want to spend $300 on a new switch, $800 on a new BCM, and hundreds more in labor to have them installed or checked out? Many people, including car dealerships (believe it or not), are now simply bypassing the passlock system. The most popular system for doing so is from this company. I have personally used their bypass module on my 2000 Chevrolet Tahoe (after trying everything but replacing the BCM) and it fixed the security problem permanently. It’s fairly expensive, but I paid 5x that at my dealership and they wanted another $1000 to replace the BCM – with no promises that would fix it! I highly recommend doing this, bypassing / disabling the entire system, so that you don’t have to keep troubleshooting every time you get stranded because the security light is going off and your car or truck won’t start.