VIDEO: GM Passlock Diagnostics – UnderhoodService
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VIDEO: GM Passlock Diagnostics

Jon Nelson discusses the GM Personalized Automobile Security System. This video is sponsored by CARDONE.

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CC: You are at the end of a repair on a GM vehicle, you might have replaced the engine or body control module, and now the engine will not start, or it runs for a few seconds and stops due to a lack of fuel.

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What is the problem? The GM Personalized Automobile Security System.

On this Pontiac G6, we just replaced the Engine Control Module due to a short to ground problem in the wiring harness. The unit is located under the hood next to the battery. Replacement is easy. The replacement ECM came pre-programmed.

Will it start? No. Is the problem with the PCM we installed? No. The issue is right here in my hands, the car doesn’t know the keys.

On just every GM model made since 1995, GM incorporated anti-theft features designed to prevent thieves from stealing a vehicle by removing the lock cylinder with a slide hammer and attempting to start the vehicle with a screwdriver, just like in the movies. The system is based on a key that can be identified by the lock cylinder. If the key matches the vehicle, the engine can be started.

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GM has made changes to the system over the years. The first systems used a key with a resistor chip. The next development was a magnet in the key that worked with a hall effect sensor in the lock cylinder. The next generation used a transponder chip in the key.

In all the systems, the lock cylinder or ring antenna communicates with a dedicated anti-theft module, body control or theft deterrent module. GM calls these systems VAT, Passlock, Passkey, Passkey II and Passkey III.

You can identify the different systems by the keys.

-This is a VATs key, with a resistor in the body of the key.

-This is a key for the Passkey and Passkey 2 system. Just like the VATs key, there is a resistor in the key’s blade. These keys can be found in both the single key and dual-key arrangements

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This is a Passlock key. It does not have a resistor. Instead, it has a magnet inside that signals a stationary hall effect sensor a coded lock cylinder. -PassKey 3 systems have a chip in the key. The easiest way to identify these keys is the stamped letters PK3 at the base of the key.

When a new ECM, BCM or Theft Control Module is installed, the key codes are lost. The modules must relearn the keys for the vehicle so it will start.

The key words to search for in your service information database are, Passlock, Passkey or VTD.

The Passkey III system on this G6 does not require a scan tool to relearn the keys, just a little time, patience and maybe a stopwatch. Let’s get started…

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This video is sponsored by CARDONE.

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