INS & OUTS OF VEHICLE ANTITHEFT SYSTEMS, THE

Motor,  Apr 2006  by Pattengale, Bob

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Without the necessary service information and tools, you may have more trouble negotiating the intricacies of a factory antitheft system than a slimjim-equipped 'professional.'

Vehicle antitheft systems vary in design and application, but their primary purpose is to prevent unauthorized vehicle access and theft. The remote keyless entry options on many systems also provide customer convenience and security. When the first unique ignition keys and door locks were introduced, engineers undoubtedly thought they would be enough to prevent vehicle theft. Over the years we've seen many changes to vehicle antitheft systems to improve on those original design intentions.

Diagnosing these systems requires knowing how they interact with the vehide and other systems, and is a significant challenge. For example, General Motors' 2004 technical service bulletin (TSB) "Emissions - Catalytic Converter Damage/Misfire Codes Set" (No. 0206-05-004A) suggests looking for aftermarket alarm systems if you have misfire diagnostic trouble codes (DTCs) P03XX, P1380 or P1381, or catalytic converter damage. The bulletin points out that some aftermarket alarm systems designed to interrupt the ignition circuit may intermittently disengage the ignition circuit while the vehicle is being driven. The ignition circuit disruptions, which occur in milliseconds, can create misfires and cause excessive fuel to be delivered to the catalytic converter, which ultimately may damage it.

The TSB recommends changing the alarm system disable point from the ignition circuit to the starter circuit. What are the chances you'd be looking at an after-market alarm system as a cause for misfire or catalytic converter DTCs? If you're attempting to correct a no-start or driveabiliry issue, don't overlook an aftermarket alarm system, and don't forget to check for any applicable TSBs.

If you suspect an alarm system might be the source of the problem, the first step is to determine who designed and installed the system. The system may be original equipment installed at the factory, an OE system installed at the dealership, an aftermarket (non-OE) system installed at the dealership or an aftermarket system installed privately. For example, a late-model Dodge Durango might have the factory-installed Sentry Key Immobilizer System (SKIS). Or, if a customer purchases a Durango without the SKIS system, he can request a factory electronic vehicle security (EVS) system, with remote keyless entry.

An EVS security system module is shown in photos IA and IB on page 50. Depending on the dealership, you might find additional antitheft options, like MobileGuardian, which can track the vehicle with a GPS transponder and disable the vehicle once the key is turned off. The customer might also decide to visit a car stereo installation shop and have an aftermarket system installed. Your diagnostic options will be directed by the system or systems that are installed on the vehicle and the service information that's available. If you're dealing with an aftermarket alarm system that lacks adequate documentation, your only option may be to disable or remove the system.

Many antitheft problems begin as an intermittent issue, which makes them difficult to diagnose. The problem will normally get worse over time, which means you'll eventually find the problem, but the customer may not be pleased with the amount of time required.

In cases such as this, it's important for the service advisor to get as many details as possible. He should ask the customer if a nonfactory alarm system or starter-interrupt system is installed on the vehicle. This should be a standard question when the vehicle is checked in for service. Some vehicles require a special key or magnet to start. If the customer forgets and leaves only the ignition key, this will delay work. The service advisor should also ask these further specific questions:

* When did the problem begin?

* Have any accessories recently been added to the vehicle?

* How often does the problem occur (once a day, several times a day, etc.)?

* When does the problem occur (cold weather, hot weather, wet conditions, etc.)?

* What does it normally take to get the vehicle to start (jiggle the key, several key cycles, wait a specific period of time, etc.)?

* Is there a specific key that's causing the problem? Perhaps the problem happens for the wife, but the husband has a different key and it never happens for him. Make sure you have the key that causes the problem.

* Are there other transponder keys on the key ring? Also, look for wireless gas passkey transponders.

* Does the security light blink or flash at times? In most cases, once the vehicle is started it will remain running even if a problem occurs. But if the security light blinks or flashes while the vehicle is being driven, it may help with the diagnosis.

Diagnosing OE Antitheft Systems

One issue in diagnosing factory-installed antitheft systems is having the correct tools for the job. In order to efficiently diagnose OE theft-deterrent systems, you'll need the factory scan tool. The OE service information may require the technician to perform pinpoint tests with a DVOM, but the primary focus will be following steps with the scan tool.