Q: Anti theft problem

asked by on June 20, 2016

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.

Electric Problems Inspection $79.99 - $99.99 Get a Quote

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.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing


Experienced Mechanic?

Earn up to $70/hr

What others are asking

2011 VW Jetta, car key comes in and out of ignition no problem, it just won't turn to start the car

Power Steering return hose leak

Hi There, You are likely correct in that if the leak is not coming from the high pressure line, it may be leaking from the return lines. I would suggest having a professional from YourMechanic come to your location to...

2003 lincoln ls v6. P2270 code is read on scanner. I've changed the catalytic converter but the code is still coming back.

Hi there. The code of P2270 is coming up for an issue that is causing the emissions to be out of calibration. Check the following conditions on your engine. Check For an exhaust leak near O2 sensor For a...

The car was running fine a week ago. The check engine light kept coming on when the throttle was above 2000 rpm's.

Hi and thanks for contacting Your Mechanic. Check the engine light for any other codes that would appear. This will direct you in the direction that is having a fault. If your engine is having an issue with the rpm's...

Jerking/studdering problem

Hi, thanks for writing in. This is a common sign of a failing mass air flow sensor. This is a unit that regulates the air flow into the engine as it is mixed with fuel prior to being injected into...

My car idles roughly and wants to die when I give it gas what could this be?

With this kind of engine issue, I would imagine that your Check Engine Light is on, indicating that the built in diagnostics have logged and error and a diagnostic trouble code. It will be important to know these codes to...

Problem with shifting positions

It may very well be that your vehicle has a problem that is causing reduced power output. Some such things could be: Faulty fuel pump Faulty oxygen sensor Vacuum leak When any of these occur, the...

transmission

It sounds like you are having a problem with your transmission's shifting mechanisms. Have the shift linkage checked to see if the cable bushings are worn out. A mechanic, like one from YourMechanic, can give your car's transmission an inspection...

Key gets stuck in the ignition and is hard to get out

Provided that you can turn your key to the off position where you would normally pull it out, it appears that the tumblers in your key cylinder are sticking or binding, preventing the key from being extracted. A quick simple...

Related articles

Symptoms of a Bad or Failing Horn Switch
If the horn makes no sound or sounds different, or if you do not find any blown fuses, you may need to replace the horn switch.
5 Essential Things to Know About the Fog Lights in Your Car
Many Many of the vehicles on the road today are equipped with fog lights, although they rarely get much use from drivers. When Should You Use Your Fog Lights? Most of the time, you will never actually need to use...
Symptoms of a Bad or Failing Fuse Box
If there are bare wires, loose fuses, or broken wires in the fuse box or the fuses are burning out faster, you may need to replace the fuse box.