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Automotive passkey systems

Automotive passkey systems provide an extra level of protection for car owners. The passkey is a specially designed main vehicle key that will fit in both the door locks and the ignition.

This key is selected and programmed just for your specific vehicle. Although another key may fit into the ignition or door lock switch the system does not allow the engine to start without the correct electrical signal from this key. There are two main types of automobile passkey systems.

Resistance passkey system

A resistance key appears to be a normal key but has a small resistor built into it. When the key is inserted into the ignition switch the circuit must recognize that the resistance value is correct before the engine will start.

The resistance key type system is one of the first that was used widely on automobiles.

This system had some troubles as these resistance keys became worn and old. General Motors used a resistor that was susceptible to wear from being inserted into the lock cylinder thousands of times.

The resisters on these keys would eventually fail to provide the correct resistance value to the security system causing a no start.

When it was time to replace the key the original resistance value would have to be obtained from the vehicles security system to cut replacement keys.

For many this was the first time that they were unable to go to a hardware store to get a duplicate car key made.

Instead a trip to the dealership was necessary and a total cost of about $30 was the average bill.

The older Gm system was known as VATS (vehicle anti theft system). The dealership parts department that would sell and make replacement keys had a tool called the VATS interrogator.

This would supply the resistance value of the blank to be used for the replacement keys.

The transponder or passkey systems

Transponder keys are based on a communications between the vehicles power train control module and the transponder in the key itself.

Each time the key is inserted into the ignition switch the pcm sends out a different radio signal. If the key's transponder is not capable of returning the same signal the engine will not start.

Some late-model vehicles use the ignition kill system that prevents the vehicle from being hot-wired. In fact, when the ignition kill is activated, not even the ignition key starts the car.

The ignition kill system has a definite advantage as a theft deterrent. There is nothing to program, no codes to remember, and nothing visible on the exterior of the car or to alert a thief this system is being used.

Automotive passkey systems

On some passkey systems, a new password must be learned by the PCM when the vehicles main control module has been replaced. If the computer is replaced the calibration is flashed into the new unit.

After the calibration is complete you can attempt to start the vehicle. It will not, but leave the ignition on until the theft system-warning lamp turns off.

Then turn the ignition off and attempt to start the engine again, the engine should start this time as the learning procedure is completed.

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