Questions and Answers
Rebuilding A Jeep Grand Cherokee Alarm System
Q. Vince, I just found your site and for a do it yourselfer like me it's wonderful! Thank you for doing this. I do have a question for you though.
I am currently restoring my neighbor's 1993 Jeep Grand Cherokee with the 4.0 liter engine. The vehicle was abused tremendously and the overhead console is missing along with the keyless sensors etc. Every time it is unlocked he has to unlock the tailgate to deactivate the security system. What are my options to:
- Dismantle the system?
- Put the system back together?
Can I junkyard salvage keyless sensors and get a new programmable remote? Where is the VTSS module you mentioned in your other articles and will simply removing it do away with this inconvenience?
Any advice you have will be much appreciated, I'm trying to give him a decent running car for when he leaves for Coast Guard basic training next week.
Mary Esther, FL
A. Let's first look at the system and how it works. This will help us understand what is involved and how it is integrated into the vehicle.
The Vehicle Theft Alarm (VTA) is a logic-controlled system. It monitors the vehicle doors, hood, trunk or lift gate, key cylinder, and ignition for unauthorized operation.
The system has the following components:
- Vehicle Theft Alarm Module
- two door ajar switches
- hood ajar switch and striker
- two door key cylinder disarming switches
- instrument panel ser lamp
- engine controller
- horn and horn relay
- park and tail lamps
- power door lock circuits
- ignition switch
When something triggers the alarm, the system will signal for about 18 minutes. For the first three minutes the horn will sound. Then the park and turn signal lights will flash for another 15 minutes.
Tamper Alert: If the horn sounds three times when either front door is unlocked, the alarm was activated. Check the vehicle for tampering.
Manual Override: The system will not arm if the doors are locked using the key or the manual lock control.
When an unauthorized entry into the vehicle occurs, the VTA module sends a message via the CCD bus to the engine controller that it is not OK to start the engine. The engine controller then zeroes out the pulse width to the fuel injectors after the engine has been started, thus shutting down the engine (start and stall condition).
The engine will not start until the system is disarmed.
The VTA module has the capability of providing bias on the CCD bus when the body controller is powered down.
To avoid both an audible alarm and the engine kill feature causing a problem in the assembly plant, an initialization procedure is included in the VTA system. This procedure requires that the vehicle has recorded 20 engine cranks. Therefore, the VTA system will be functional on all vehicles and will require dealer verification.
To verify the system, proceed as follows:
- Open the driver's door.
- Remove the ignition key (but keep it in hand).
- Lock the doors with the power lock switch.
- Close the driver's door.
- If the instrument panel theft alarm "SET" lamp flashed, the system is operational and verified. If not, 20 engine cranks have not occurred, or there is a problem with the theft alarm system.
To dismantle the system, all you need to do is remove the Vehicle Theft Security System Module (VTSS) and whatever sensors may be left in the vehicle.
You can get whatever sensors or switches from a junkyard vehicle and put the system back together. It's just a matter of finding what is missing and replacing it. Once all the parts are replaced, the VTSS should begin to work properly. You can get up to four RKE transmitters for the system.
This is the procedure to reset the VTSS module.
Alarm Module Reset Procedure
NOTE: This information applies to a Vehicle Theft Security System (VTSS) that was armed when the battery was disconnected and reconnected.
When the armed VTSS senses that the battery has been disconnected and reconnected, it enters its power-up mode. In the power-up mode the alarm system remains armed following a battery failure or disconnect. If the VTSS was armed prior to a battery disconnect or failure, the system will have to be actively or passively disarmed following a battery reconnection.
The power-up mode will also apply if the battery goes dead while the system is armed and battery jump-starting is attempted. The engine no-run feature will prevent the engine from starting until the alarm system has been actively or passively disarmed.
Passive disarming of the Vehicle Theft Security System (VTSS) occurs when the vehicle is unlocked using the key to unlock either front door or the lift gate. Active disarming of the VTSS occurs when the vehicle is unlocked by depressing the Unlock button of the Remote Keyless Entry (RKE) transmitter.
Once the alarm has been activated (horn sounding, lights flashing, and the engine no-run feature), either disarming method will deactivate the alarm.
Depressing the Panic button (if equipped) on the RKE transmitter will also disarm the VTSS, but the horn will sound and the lights will flash for about three minutes as part of the Panic feature. The horn and lights can be stopped by pressing any of the RKE transmitter's buttons or driving the vehicle above 15 mph.