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Does the starter engage, or you get nothing when you try to start? The PassLock system does not prevent the engine from turning over. The only thing that PassLock does is keep the injectors from operating, thus preventing a start. Usually, if there is a problem with the PassLock, the security light will flash when the key is turned to "start".

 

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If nothing happens when you turn the key to "start" you have a problem not related to the security system. That doesn't rule out the possibility of a PassLock issue also. Just that PassLock doesn't prevent the starter from operating. Do you hear a clicking sound from under the hood when you turn the key to "start"? How old is the battery? Have you checked the battery cables?

Whether or not this is a Dealer fix will depend entirely on your troubleshooting and mechanical skills.

 

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For trucks produced for the US market: other than the ignition switch and the security light, there are two main components in the PassLock system.

BCM; (From the GM Service Manual.) The BCM contains the logic of the theft deterrent system. The BCM provides the 5-volt reference to operate the security resistor. The BCM also measures the voltage of the off/run/crank voltage. The voltage measured will indicate whether the security resistor has been activated and whether the resistance value is a valid value or the tamper value. If voltage measured is in the valid range, the BCM compares this voltage to a previously learned voltage code. If the voltage codes match, the BCM sends a serial data message containing fuel enable password to the engine control module (ECM). If the voltage codes do not match, the voltage is in the tamper range, or there is a circuit fault, the BCM will not send a start disable password to the ECM, and the vehicle will not start.

ECM: (From the GM Service Manual.) The ECM contains the remainder of the logic of the immobilizer system. If a serial data message containing a valid fuel enable password is received from the BCM, the ECM will continue to allow the fuel injectors to operate. The ECM will allow the fuel injectors to operate until it decides there is no valid password coming from the BCM. If the ECM does not receive a serial data message, or receives a serial data message with an incorrect password, the engine will crank and will not run or will start and stall immediately