Automotive Passkey Systems

Ignition lock cylinderIgnition Lock Cylinder

Find out how automotive passkey systems provide an extra level of protection for car owners.

Review some common problems associated with this technology. The passkey is a specially designed main vehicle key that will fit in the door locks, trunk and the ignition.

What is a valet key? On many cars the valet key won't work the trunk lock, so it can remain a secure area. The main key is selected and programmed just for your specific vehicle.

Although another key may fit into the ignition or door lock switch, the system doesn't allow the engine to start without the correct electrical signal from this key. There are two main types of automobile passkey systems.

Resister Type 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 value to the security system.

Unfortunately, this can cause a no start condition. When it's time to replace the main key the original resistance value would have to be obtained from the vehicles security system to cut the replacement keys on the properly coded blank.

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.

They called the older General Motors system VATS or vehicle anti theft system. The dealership parts department selling 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 Coded Transponder Key Systems

GM passkey diagnosis manualGM Passkey Manual

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 power control module 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.

But what if it malfunctions? If you have an old GM VATS system they now make a kit to bypass it. 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 start, 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. Of course, there is nothing wrong with old fashioned non electronic theft deterrent systems like the Club.

The tire club has been around for years and is highly visible and a great theft deterrent. It requires no maintenance or batteries and will never cause an automobile not to start.

My pages about key less entry and security systems are available from this next link about car alarms.

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