PassKey III
This system uses a special key (PK3 stamped on the shoulder of the key) with a transponder under the rubber cover. The receiver module is located next to the lock cylinder. When the key is positioned next to the lock cylinder receiver module, it energizes the transponder which sends a coded signal to the receiver. The receiver module checks its memory to see if the signal is correct. If it is, the module sends a signal to the PCM to enable the engine. If the value is valid, the indicator light will remain steady for 2 seconds. You cannot test this system with an ohmmeter. You need a scan tool. If the signal is not correct, the PCM disables the injector and the starter and flashes the light once per second. If an illegitimate key is used or a system problem exists, the light flashes twice per second.
Maybe check this?^^^^^^^^
All I can think of is the new PCM/VIN is incorrect, a conflict between the PK3 receiver/BCM and the PCM.
An exciter located at the opening of the lock cylinder activates as the key is inserted. The exciter sends a radio signal that’s received by the transponder. The signal actually energizes the chip in the key head and the key responds by broadcasting a unique identity code that’s received by the Theft Deterrent Exciter Module (TDEM). The TDEM transmits the data to the BCM. The BCM consults its memory and if the identify code matches, it sends a fuel enable code to the PCM. If wrong, the BCM sends a fuel disable code to the PCM. The BCM is also equipped to detect an
![theft deterrent exciter module]()
intermittent condition with the transponder. If it loses the code for one second, it sends a fuel disable code to the PCM and the vehicle won’t start. That’s why it’s always best to try a different key if you encounter a car won’t start security
This system uses a special key (PK3 stamped on the shoulder of the key) with a transponder under the rubber cover. The receiver module is located next to the lock cylinder. When the key is positioned next to the lock cylinder receiver module, it energizes the transponder which sends a coded signal to the receiver. The receiver module checks its memory to see if the signal is correct. If it is, the module sends a signal to the PCM to enable the engine. If the value is valid, the indicator light will remain steady for 2 seconds. You cannot test this system with an ohmmeter. You need a scan tool. If the signal is not correct, the PCM disables the injector and the starter and flashes the light once per second. If an illegitimate key is used or a system problem exists, the light flashes twice per second.
Maybe check this?^^^^^^^^
All I can think of is the new PCM/VIN is incorrect, a conflict between the PK3 receiver/BCM and the PCM.
GM PassKey and PassLock overview
How the GM PassKey and PassLock anti-theft systems work.
ricksfreeautorepairadvice.com
An exciter located at the opening of the lock cylinder activates as the key is inserted. The exciter sends a radio signal that’s received by the transponder. The signal actually energizes the chip in the key head and the key responds by broadcasting a unique identity code that’s received by the Theft Deterrent Exciter Module (TDEM). The TDEM transmits the data to the BCM. The BCM consults its memory and if the identify code matches, it sends a fuel enable code to the PCM. If wrong, the BCM sends a fuel disable code to the PCM. The BCM is also equipped to detect an
intermittent condition with the transponder. If it loses the code for one second, it sends a fuel disable code to the PCM and the vehicle won’t start. That’s why it’s always best to try a different key if you encounter a car won’t start security
PassKey III system
If you own a GM vehicle with PassKey III antitheft or a previous PassKey II or PassLock system and have a car won’t start security light on, this article is for you.
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