General Motors Vehicles Equipped with PASSLock

The PassLock system was designed to prevent vehicle theft by disabling fuel to the engine if attempts are made to start the vehicle without the correct bitted key. PASSLock increased the level of security while retaining the ease of service and costs offered by standard ignition lock systems. Unlike the General Motors PASSKey I/II, VATS, PASSKey III, or keyless, the security of the PassLock system is built into the lock and is not dependent on a specialized key or separate device.

NOTE: For the purpose of this article, the terms PassLock, Magnetic Resonance Device (MRD) and Vehicle Theft Deterrent (VTD) are interchangeable.

No programming is required for the PASSLock-equipped vehicle to accept additional keys. Any key blank with the proper profile cut to the correct depths can be used to operate the ignition lock.

For the 1995-1/2 model year, General Motors introduced PASSLock, the first ignition lock equipped with a magnet mounted into the ignition lock cylinder and a corresponding Hall-effect sensor mounted into the housing assembly. When the correctly cut key is inserted into the lock cylinder and rotated, the magnet registers on the sensor’s three switch points. The sensor electronically signals the vehicle’s on-board computer, and the fuel supply remains on if the electronic value matches the code stored in the computer.

If the values do not match, the fuel supply is shut off. After three consecutive failed attempts, PASSLock will enter Long Tamper Mode, disabling the engine for 10 minutes while the Theft System indicator on the instrument panel flashes.

The PASSLock system is designed such that forced rotation normally damages the electronics, immobilizing the vehicle. According to General Motors, should the ignition lock be force rotated, the lock must be replaced in order to operate the vehicle.

Note: The theft deterrent function of the PASSLock System locks out the fuel injectors after the engine is started. However, before a tamper mode engages, the car may run for a few seconds. The engine will then stall.

PASSLock was developed for the General Motors 10-cut lock mechanism. There are three basic styles of PassLock ignition locks: Modular, Modular in-dash, and CSS. When purchasing a replacement ignition lock, make sure the part number is correct for the year, make, and model. PASSLock ignition locks vary by the version (PASSLock I or II), the type of connector, and if wired, the length of the wire. Installing the incorrect ignition lock will usually result in the vehicle not being operable.

Depending upon the year and the model, replacing the ignition lock can result in the need to disassemble the dashboard. Early vehicles equipped with the modular PASSLock ignition locks had a long wire that went from the ignition switch to a connector behind the instrument panel. The modular in-dash ignition locks and the CSS ignition lock cylinders do not have wiring that must be plugged in.

When replacing a PASSLock ignition lock, there is a one in 10 chance the Hall effect sensor is the same value as the lock being replaced. Replacement locks do not have an identified sensor value. When the starter is engaged for the first time and the engine starts but stalls, the instrument panel security light will flash, indicating the vehicle is in the secure mode (it will not start) and must be programmed to accept the new lock.

To reprogram PASSLock I ignition lock:

Step 1. After replacing the lock, try to start the vehicle with a correctly cut key. There is a one in 10 chance that the car will start.

Step 2. If the new lock does not match the electronic value in the vehicle’s computer, an indicator light on the instrument panel will begin flashing and the car will be disabled.