I have a '99 Chevy Tahoe with a 5.7L Vortec engine. After I start the engine the security light on the dashboard will go on and stay on. I'm able to start the engine sometimes, with difficulty.
The security light is part of the Passlock system and is not working properly. I checked the fuses and used another key but neither helped.
Passlock is a second generation General Motors' theft deterrent system. With the use of a Passlock sensor (mounted in the steering column) the Passlock system can determine improper ignition key and lock cylinder operation by monitoring magnetic fields emitted by the lock cylinder assembly. Once improper operation is confirmed, engine startup is disabled.
The Passlock system eliminated the resistor chip mounted in the ignition key used by the previous Passkey system, including the headaches and expense that went along with it.
Passlock is a subsystem of the vehicle's Powertrain Control Module. The Passlock sensor sends a signal to the Passlock control module. The Passlock module reads this signal and sends the appropriate information to the Powertrain Control Module. If the ignition key and lock cylinder operates normally the engine will start as usual. If it was operated improperly the Powertrain Control Module will be directed to disable fuel injector operation, prevent engine startup, and there will be a diagnostic trouble code set in the Passlock Control Module's memory.
I just wanted to give you an understanding of system operation. It's gonna require the correct scan tool for proper diagnosis. Weak links are the circuits to and from the Passlock Sensor in the steering column. It's a very sensitive signal and can be easily affected by shoddy electrical connections.
If a scan tool displays diagnostic trouble code B2960 (Passlock sensor voltage out of range), the next step would be a resistance check and a complete inspection of connections and wiring involving the sensor. Pay the diagnostic time at a heads-up auto repair shop.