Pattengale, Bob

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.

In some cases, access to the antitheft or immobilizer data is restricted to dealership personnel, even if you have the factory scan tool. The screen captures in photos 2A and 2B are from a Vetronix 3100 Mastertech, running Honda software. If you select the immobilizer option, the next screen shows “Test not available.” At present, only Honda dealerships have access to the necessary scan tool software to repair these systems. The National Automotive Service Task Force (NASTF) has formed a security committee to address issues for locksmiths, as they relate to immobilizer systems. Most vehicle manufacturers are looking for solutions to help shop owners deal with antitheft and immobilizer issues.

Many vehicle manufacturers have two types of antitheft systems. The first is a system that’s designed to draw attention when someone attempts to break into the vehicle. The horn sounds and the headlamps and park lamps flash. The GM version of this system type is called the Content Theft Deterrent (CTD) system.

The second antitheft system type prevents the vehicle from starting. The GM system is called Vehicle Theft Deterrent (VTD) or Passlock, the Ford system is called Passive Anti-Theft System (PATS) and the Chrysler system is called Sentry Key Immobilizer System (SKIS). Most of these systems use a key with transponder, transponder receiver, transponder module and powertrain control module (PCM). In some cases the transponder receiver and module are combined in a single component.

Operation is simple. The transponder-equipped key is inserted into the ignition cylinder and the ignition switch is turned on. The transponder module wakes up and checks the transponder receiver to determine if the appropriate key was used. If the key matches, the transponder module sends a signal to the PCM authorizing vehicle start. If the key does not match, the vehicle will not start and the security lamp will flash. Checking the security lamp is the quickest way to determine if the antitheft system is operating properly.

Here’s a rundown of several of the OE theft-deterrent systems out there:

GM Antitheft System. The GM VTD or Passlock system uses the body control module (BCM) and ignition lock cylinder to activate the start function. The ignition cylinder uses a magnet that produces a unique voltage value when rotated in the ignition housing across the Hall effect sensor. The BCM compares this voltage value to the value stored in the BCM. If the voltage values are the same, the BCM sends a signal to the powertrain control module to enable fuel. If the voltage values are not the same, the engine will briefly start, then stall.

There are two ways to determine if the Passlock system is the cause of a nostart condition. The quickest way is to look at the security indicator lamp on the instrument panel. If it’s flashing after an attempted start, the fuel disable command has been energized. The second method is to use a scan tool to check the antitheft or fuel system status parameter. If the parameter shows “fuel system disabled” or a similar description, then it’s a Passlock issue.

Fig. 1 on this page is a Vetronix Tech 2 screen capture taken from a 2000 GMC Denali, using the Powertrain section. The DTC present is a P1631-‘Theft Deterrent System – Password Incorrect.” This general trouble code indicates the correct password was not received to initiate vehicle start, but does not provide a suggestion for the failure. The failure record data did not provide any diagnostic help.

The next step is to check for BCM trouble codes. In this case, a B2960 was stored, which relates to the BCM monitoring the Passlock Data Voltage. The Tech 2 is the only scan tool capable of displaying Passlock parameters. The Vetronix 3100 Mastertech will now display the Passlock data on 2004 and newer GM vehicles. Fig. 2 shows the data from the Passlock section of the Tech 2. The Passlock Data Voltage (red graph) and Passlock Code (green graph) parameters are graphed. The graph shows the Passlock code changing from Valid Code 2 to Valid Code 3. This should remain stable while driving.

The diagnostic flow chart for this DTC recommends monitoring the Passlock Data Voltage for approximately one minute. The voltage value should not change by more than ± .02 volt. The peak voltage on this vehicle is 1.67 volts and the low voltage is 1.29 volts, which exceeds the recommended voltage vanation. The ignition housing was the cause in this case. Also check the connection points between the ignition housing and BCM.

If you don’t have a Tech 2, you still have a few options in diagnosing the Passlock system. The Passlock Data Voltage can be checked with a voltmeter or lab scope. If the voltage does not remain steady as explained above, you could reach the same conclusion-the ignition housing/Hall effect sensor might be at fault.

If the condition is a no-start, monitor the Passlock Data Voltage. If the voltage does not change from 5 volts, check the ignition housing. The Passlock Data Voltage has a potential of 10 different values, ranging from .86 to 4.28 volts. If the voltage changes but does not permit a start, you’ll need the Tech 2 to complete the diagnosis.

If you retrieve a Passlock DTC on a GM truck in the Powertrain section but no DTCs are present in the BCM, check the Ignition 1 voltage supply to the BCM. The Ignition 1 voltage is used to initialize the Passlock software in the BCM. If Ignition 1 input voltage is lost, the engine will start briefly, then stall-similar to the behavior when an incorrect password is detected. But when you check for BCM Passlock DTCs, none will be present, because the Passlock software was not initialized.

Toyota/Lexus Antitheft System. Photo group 3 above shows three scan tool captures taken from a 2004 Lexus ES 330. The first capture is with the key out of the ignition switch, the second is with the key in the ignition switch and the third shows the antenna coil parameter.

The scan tool data is essential to diagnosing the Toyota system. For example, the Antenna Coil parameter can read Normal or Fail. The value of Normal has two potential meanings. If the immobilizer system is malfunctioning and a B2784 “Antenna Coil Open/Short” DTC is retrieved, the Toyota diagnostic data points to replacing the transponder key ECU. If the scan tool value shown is Fail with the B2784 code, the diagnostic data points to checking the wiring between the transponder key ECU and transponder key amplifier, if the wiring checks good, the diagnostic data recommends replacing the amplifier.

If you don’t have the enhanced diagnostic data, you might be able to retrieve the fault code with another scan tool, but you wouldn’t know in which direction to begin the diagnostic process. The parameter value provides that direction.

Toyota Smart Entry System. Some Toyota vehicles are now equipped with a Smart Entry system. Photos 4A and 4B on page 56 show two components of the Prius Smart Entry system. The Prius does not use a normal key or ignition switch system. The Smart Entry system controls the locking and unlocking of the doors and permits vehicle starting.

To unlock the vehicle, the system automatically checks the key ID code when the customer gets within two to three feet of the driver’s door handle. The Smart Entry system assumes the unlock standby condition, waiting for the handle to be touched. Once it’s touched, the drivers door or all doors unlock.

To lock the vehicle, the customer gets out, then presses the trigger switch on the door handle. The Smart Entry ECU checks the ID code and verifies that the smart key is outside the vehicle, then locks the doors.

Starting a Smart Entry-equipped vehicle is quite complex when you look at all the steps that are performed, but everything happens very quickly. Many failsafe options also are included in this system.

Honda Antitheft System. Honda introduced the Type 1 immobilizer system on 1997 to 2001 Preludes. Photo 5 shows an ignition switch and key set for a 1998 Honda Prelude. “T5” stamped on the key shank indicates that it’s a duplicate key. This will help you determine which key is a master key.

What happens if the driver decides to use the red learning key? The black key is the master key and the gray key is the valet key. The red learning key is used only for key reprogramming issues. If the customer lost a key and decided to use the learning key, it will scramble the programmed memory and possibly damage the immobilizer unit. The only fix is to work with a local Honda dealership. Key reprogramming requires the factory scan tool and access to specifie passwords. The good news is Honda provided a way for the vehicle to be started once and driven to the dealership or home for spare keys.

The customer needs a nontransponder key cut to the ignition system. Next, he must ask for the immobilizer five-digit brake code. The customer turns the ignition switch to the ON position, then uses the parking brake to enter the first digit of the five-digit code. The ignition switch is turned off and the first digit is stored into the immobilizer unit. The sequence is repeated for the remaining digits of the code. This should allow the vehicle to start. This procedure will not work if the red learning key was used for starting purposes.

Once again, Honda does not make immobilizer data available to the aftermarket at this time, so your best way of knowing if the security system is causing a problem is to watch the immobilizer system indicator (a flashing key). The indicator should flash for approximately two seconds when started and for five seconds when the key is removed. If a problem exists in the system or if the wrong key is used, the light will continue to flash. Because service information is limited, it’s unwise to spend time attempting to fix a no-start that’s caused by the immobilizer system.

Ford & Chrysler Antitheft System. Up to this point, I’ve stressed the importance of access to a factory scan tool and the necessary software for effective OE antitheft system diagnosis and repair. The argument has been made that releasing this information to the aftermarket could cause a security issue for vehicle owners if the information were to fall into the wrong hands.

There’s reason to believe this situation may change, and evidence that the change may have already begun. For example, an excellent document detailing tlie Ford PATS system is available on the nonsubscription, free side of the Ford service information website. Use die following link to retrieve the PDF file: retail/pain Job _a id. pdf

In a related note on the Ford PATS system, be aware that if a DTC P1260 is stored, the PCM is disabled due to a PATS issue.

Chrysler TSB 08-015-05 explains how to deal with SKIS and PCM initialization. The bulletin also discusses what to do if you’re replacing the PCM and don’t have a DRB III to reset the SKIS code.

Photo 6 shows one type of antitheft key. Many keyless entry systems use a battery to energize the transponder assembly inside the key. Transponder-type keys, on the other hand, require no maintenance or battery replacement. Some shops include checking battery condition as a service to customers. Make sure you understand how to reprogram the key once the battery is replaced.


Diagnosing vehicle antitheft systems can be straightforward, if you have good service information and the correct tools. The key to getting started in the right direction is to thoroughly research the problem. Identify the type of system you’re dealing with. If it’s an aftermarket system, it may not be repairable. If it’s an OE system and you don’t have the tools or information, you may want to sublet the repair or look for a creative solution-maybe another shop in the area has the factory scan tool. The hope is that these scan tool gaps will be corrected in the future, and that aftermarket scan tools will he able to provide diagnostic access to all vehicle antitheft systems.

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Copyright Hearst Business Publishing Apr 2006

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