GM Passlock Security System

Many FixYa posts are asking for ways to bypass the security system and immobilizer. This is what you are up against and explains how the system works. Thanks to our FixYa Professional Vehicle Electronics Wizard Jeff Armer for the factory explanation.

Passlock™ System

The Passlock™ System is provided in order to prevent vehicle theft if the ignition lock cylinder is forced to rotate or the ignition switch is operated while separated from the ignition lock cylinder case. If starting is attempted without authorization from the Passlock™ System, the powertrain control module (PCM) will disable engine starting. Start disable may be in the form of fuel disable or starter disable, depending on engine application.

The components of the Passlock™ System are as follows:

• The ignition lock cylinder and key

• The ignition lock cylinder case, including the Passlock™ sensor

• The ignition switch

• The body control module (BCM)

• The security indicator on the instrument cluster

• The powertrain control module (PCM)

Ignition Lock Cylinder Case, Including the Passlock™ Sensor
The ignition lock cylinder fits inside the ignition lock cylinder case and operates the ignition switch when turned by a key with the proper mechanical cut. When the ignition key is used to turn the ignition lock cylinder to crank, start, a magnet on the lock cylinder passes close to the Passlock™ sensor within the ignition lock cylinder case. The magnet activates the security hall effect sensor in the Passlock™ sensor which completes a circuit from the security sensor signal circuit through a resistor to the security sensor low reference circuit. The resistance value will vary from vehicle to vehicle.

If a magnet from outside of the ignition lock cylinder case is used to attempt to steal the vehicle, the tamper hall effect sensor will be activated. This completes a circuit from the security sensor signal circuit through a tamper resistor to the security sensor low reference circuit bypassing the security resistor. If the ignition switch is forced to rotate without the correct key, or if the ignition lock cylinder is removed by force, the Passlock™ sensor will be damaged and will not operate.

May forums suggest connecting a resister into the transponder receiver circuit, but jumping a 2200 ohms resistor into the wiring of the pass-lock system will do nothing.