http://www.gmupfitter.com/files/media/photo/284/Bulletin_20.pdf
PASSLOCK
The Passlock system is designed to prevent vehicle operation if the key is not used to start the vehicle. The key, which does not contain a resistor will turn the Passlock lock cylinder. The Passlock lock cylinder will relay a resistance code to the instrument panel cluster (IPC). It does this by rotating a magnet past a stationary hall effect sensor, creating a resistance code. At this point the IPC will determine if the resistance code is correct and within an acceptable time frame. If the code is correct, the IPC will send a coded password to the powertrain control module (PCM). If the PCM receives the correct password, it will allow the fuel injectors to operate normally and the vehicle will start and run normally. If the correct resistance code from the lock cylinder is not received within the acceptable time frame, the vehicle will go into a short tamper mode during which the theft deterrent system will not allow the vehicle to operate for approximately 4 seconds. When this occurs, the security indicator will flash. After three consecutive failed tries, the system will enter into a long tamper mode. In this mode, the fuel injectors will be disabled for approximately 10 minutes, and the security indicator will be flashing. Please note that in any of the tamper modes, the vehicle may start, but it will quickly stall.
Default
The Passlock system is designed to prevent vehicle theft even if any of the theft deterrent parts are replaced. Passlock eliminates the need for the key mounted resistor. Parts that can no longer be replaced without the possibility of the system going into a tamper mode and prevent starting are: the lock cylinder, the instrument panel cluster (IPC), and the powertrain control module (PCM).
In order to initiate the relearn:
1. Hook up your scan tool to erase any of the passlock/vehicle theft deterrent trouble codes. If there are any other codes, note them before you erase them, so you may address them after the relearn has been completed.
2. With the ignition key in the “On” position from the code-clearing step, attempt to start the vehicle. At this point, if the vehicle starts, and the security light has not illuminated, a relearn is not necessary, and you’re done. If the vehicle starts and stalls, leave the key in the “Run” position and wait for the “Security” light to turn off. This will take approximately 10 minutes. At any time during this relearn, the light may flash or be on steady. If the ignition switch is turned off at any time during this relearn cycle that the security light is illuminated, the entire cycle must be restarted from the beginning. For most cars, one cycle will be sufficient for the relearn. If the vehicle will not start after the first cycle, then continue the process from step #3 to the end. Most trucks will require that you continue from step #3 to the end.
3. When the light turns off, turn the ignition switch to the “Off” position for approximately ten seconds.
4. Next, repeat steps 2 and 3 two more times for a total of three cycles. After the third time, the new code will be relearned on the next start attempt when the ignition switch is rotated from the “Off” position.
5. From the “Off” position, start the vehicle, observing the security light. If the vehicle starts and runs normally, and the security light is off, the relearn is complete. If the vehicle does not start, check for trouble codes before proceeding further.
