Skip the auto shop - Our mechanics make house calls

Q: Anti theft problem

asked by on

I think there is a short in the anti theft system. Will taking out the 7.5 anti theft fuse will that stop the alarm system?

My car has 177777 miles.
My car has an automatic transmission.

A: Rarely will pulling a fuse disable an anti-...

Rarely will pulling a fuse disable an anti-theft system. If it were that easy, thieves would figure that out quickly and more cars would be stolen. Fortunately, most factory alarms are usually fairly simple to diagnose but very difficult to bypass. By far, the most common failure are the door switches.

The door switches that turn on the interior lights and will light the red door light on your dash when you open a door or the door is ajar are the most common and easily overlooked failures. These same switches inform the BCM (body control module) when a door is opened without a key. If your door ajar light comes on while driving, this could be your problem. To test the switches, simply open doors one at a time and observe the door ajar light on the dash. If you open a door and the light doesn't turn on, you have a problem in that door. Be sure to turn the key on and open doors one at a time and keep the rest closed. The trunk and engine hood will have switches as well.

Of course, check all fuses, not just the ones you think power the BCM. Often other fuses will affect other systems even though they are not labeled as such.

If this doesn't help you figure out the problem, I personally would hook up a scanner and observe BCM data. The BCM is the primary module in the anti-theft system, but this car has door modules as well. They will monitor the lock position and window position of each door. If the data in the scanner doesn't agree with the state of the door, you have found a problem.

Other common points of failure to consider are broken wires in the door jamb wiring harness. This happens because every time the door opens, this harness will flex eventually breaking a wire or wires in the wiring harnesses to the doors.

Last, there is a relay in this system that is in the engine compartment. Relays often develop bad connections internally. If this relay is cheap, I would just replace it as a test. If not, some testing will need to be done. To test the relay, you will need a wiring diagram and some knowledge of how automotive electrical systems work. If you want to have this checked for you, a technician from YourMechanic can come and diagnose your electrical system to determine how to proceed with a repair.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%

Get a quote

What others are asking

Q: Air conditioning hissing noise - 2016 Infiniti QX60

Hello. Some vehicles may indeed emit a hissing noise as part of their normal operation, however, the noise is usually very quiet, not enough to cause a bother. If the noise is considerably loud, that may be an indicator of...

Q: Car shuts off, will not start - 1990 Mercedes-Benz 300SE

Hello. I would check for power at the fuel pump. It sounds like you have a voltage issue. Most of the time, this occurs when the fuse blows or when the fuel pump relay goes bad. These all need to...

Q: Auto shutdown relay clicks and won't stop until negative cable is off

Hi, thanks for writing in. This may suggest a short of some kind causing the power to continue to be supplied to the relay. The starter relay is a small unit near the starter that directs power to the starter...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.