The Anti-Theft System Won’t Let My Car Start一What Should I Do?

A vehicle that won’t start, won’t spin the starter, or will start and immediately die is one of the most common symptoms of a problem with the vehicle’s anti-theft system, and this problem can be a bit complicated to resolve.

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: You’ll know you have an anti-theft issue if the anti-theft light is flashing or otherwise behaving differently than it does on a normal start. However, since the anti-theft system relies on communication between different modules, there are many things that can cause the anti-theft system to prevent the car from starting.

Quick Note on Anti-Theft Systems

Passive anti-theft systems are designed to prevent the car from being stolen while perimeter anti-theft systems are designed to prevent people from stealing stuff in the car. Passive anti-theft systems prevent the car from starting if the wrong key is used or somebody is trying to hotwire the car. Meanwhile, perimeter anti-theft systems will sound an alarm if somebody opens a car door while the system is armed. This type of system won’t prevent the car from starting.

Passive anti-theft systems are designed to prevent the car from being stolen while perimeter anti-theft systems are designed to prevent people from stealing stuff in the car. Passive anti-theft systems prevent the car from starting if the wrong key is used or somebody is trying to hotwire the car. Meanwhile, perimeter anti-theft systems will sound an alarm if somebody opens a car door while the system is armed. This type of system won’t prevent the car from starting.

–Richard McCuistian, ASE Certified Master Automobile Technician

Getting Around a Malfunctioning Anti-Theft System

Note that getting around a faulty anti-theft system is a lot easier said than done on most platforms and will typically require professional help. Having said that, if you’re sure that the service theft deterrent system is the reason why your car won’t start, here are a few things you can try:

Use the Mechanical Key

Your car’s mechanical key can be used to disable a perimeter-type anti-theft system but not a passive anti-theft system.

Turning the key up to the “on” position for a few minutes can cause the anti-theft system warning light to go off and get your car to start. But again, this varies tremendously from platform to platform.

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: Turn-of-the century and early 2000s GM cars will usually disable the engine for about 20 minutes even if the key lock cylinder isn’t transmitting the proper code. This prevents a person from being stranded. But other OEMs have entirely different properties, so just turning the key on for a while won’t do anything to get you past the passive anti-theft system.

Inspect the Affected Components

First, make sure that the parking and low-beam headlights, dome and courtesy lights, horn, and electric door locks are all working as they should.

On most vehicles, these components send various signals to the powertrain control module (PCM), alerting it whenever there are issues like a missing signal and out-of-range signals.

If the PCM can identify an issue because of the signals from these components, it can disable the anti-theft system and log a diagnostic trouble code (DTC).

If all the components are operational, make sure all their switches are in their normal on and off positions via voltage drop tests. Doing so will help you identify the faulty parts and circuits.

The diagnostic and repair procedures might require extensive automotive repair knowledge, so if you’re not familiar with resolving trouble codes, it’s best to leave the job to a professional mechanic.

Accessing the Anti-Theft System

Car dealers or certified repair outlets might be the only ones who can access your vehicle’s anti-theft system, depending on its year, make, and model.

Most factory-installed anti-theft systems require specific scan tools that can be quite tricky to use if you’re not familiar with the diagnostic process.

Most vehicles with an anti-theft system come with ignition keys with a coded transponder chip that sends a signal to the receiver in the ignition switch.

If the anti-theft system sends a no-go signal to the PCM, the engine computer will disable the ignition, fuel system, or starter.

Diagnosing a Faulty Anti-Theft System

Most anti-theft systems are integrated with other electrical circuits to form a multiple-circuit system.

So when it comes to diagnosis and repair, it’s important to have make-model-specific wiring diagrams and test procedures. These will help you break down the system into subcircuits and identify the faulty component.

Other Anti-Theft Devices to Check Out

Factory-installed anti-theft systems act as immobilizers and keep your vehicle safe from thieves. But if your car doesn’t have one, you might want to check out these foolproof devices.

Steering Wheel Brake Lock

This device locks the steering wheel to the brake or clutch pedal to immobilize the vehicle. A steering wheel brake lock is made from hardened steel, so a hacksaw or power drill can’t break it.

Wheel Lock

The wheel lock works like the standard tire clamp. It prevents one of the wheels from rotating, keeping the vehicle parked in the same spot.

Faraday Bag

A Faraday bag is a small pouch that blocks electromagnetic fields that come from keyless entry systems. It’s suitable for drivers who have keyless entry systems in their vehicles, as it blocks an electronic signal that can unlock vehicle doors.

GPS Tracker

There are GPS trackers that fit onto OBD ports and provide your vehicle’s real-time location. Although a GPS tracker can’t prevent thieves from taking your car, it does come in handy when tracking your vehicle’s whereabouts.

Vehicle Theft Prevention Tips

Anti-theft systems and devices can only do so much. So, as a car owner, you must be thorough when it comes to keeping your vehicle safe. Aside from anti-theft devices, you can follow these practices to prevent theft.

Always Take the Key with You

Many drivers like to leave the engine running while they make a quick run to the restroom or nearby store, increasing the risk of someone breaking in and stealing their car.

Always take your key with you wherever you go to prevent this from happening.

Park in Well-Lit Areas

Parking in well-lit areas makes it risky for thieves to do something fishy. Doing so also makes your vehicle visible to bystanders.

Double-Check Doors and Windows

It pays to double-check your doors and windows whenever you leave the vehicle. Ensure all the windows are pulled up and the doors are locked.

Don’t Keep a Spare Key in Your Car

Thieves will always try to look for a spare key inside your car once they manage to break in. Keeping one in your glove box will make it easier for them to steal your ride.

The Bottomline

Anti-theft systems can fail like any other component in your vehicle. The cause can be a simple dead key fob battery or a complicated electrical fault.

If your car won’t start because of a bad anti-theft system, you might need to pay a trip to the nearest repair shop or dealership, especially if the system is factory-installed.