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John, Master A.S.E Automotive technician
Category: Chevy
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Experience:  A.S.E MasterTechnician A1-A8 w/L1,38 years experience General Motors Master Technician
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The horn/alarm on my 2005 Chev Malibu Maxx goes off intermitantly

Customer Question

The horn/alarm on my 2005 Chev Malibu Maxx goes off intermitantly when I am not in the car and it is locked and turned off. No pattern to it. Is this a common issue? Any suggestions as to what it is? I have reviewed the on board dash computer information screens and they seem normal.
Submitted: 5 years ago.
Category: Chevy
Expert:  John replied 5 years ago.

HelloCustomer

Any intermitten electrical problem is always harder to locate,but not necessarily harder to repair once the root cause is determined.The first place to start in the diagnosis of this problem is with a class 2 scan tool.Inspect any failure codes that may be set & view input sensors that go to the BCM (body control module) & TDM (theft deterrent module) & PCM (powertrain control module).

 

When the BCM detects an unauthorized entry, the BCM enters the alarm mode. The BCM activates the horns and exterior lamps for 30 seconds. This is followed by a 3 minute time-out with the horn and lamps no longer active. If no new intrusions are detected after the time-out, the horn and lamps are not active. The system must be disarmed or the intrusion condition removed after the time-out for the system to exit alarm mode.

The Content Theft Deterrent (CTD) System uses the door ajar switches in the door jambs as one method to activate the alarm. The body control module (BCM) monitors all door ajar switches via a discrete input from each door ajar switch, including the rear compartment. If the BCM receives a ground signal from a door ajar switch when the CTD System is armed, the BCM activates the alarm.

The body control module (BCM) monitors the following inputs:

Driver and passenger door ajar switches
The rear compartment ajar switch
Transmitter LOCK/UNLOCK buttons, internal function of the BCM
PasslockTM Status--The BCM uses the PasslockTM status for disarming the system or silencing and alarm when the correct key is used.

A good bit of the time I find the door ajar switch or connection to be at fault.
Customer: replied 5 years ago.

Thanks for the response but I do not have a class 2 scan tool. Most of what you talk about is a bit over my head so if we dumb this down is this the type of problem a laymay can troubleshoot or is it a service call to my dealer?

 

Can the alarm be disabled? If so how? If I disconnect the battery & reconnect it and then redo all the settings on the Driver Information Centre will that aleviate the problem?

 

Could this be caused by dirty contacts in the door switches? and if so how do you clean them off?

 

Thanks

Expert:  John replied 5 years ago.

To diagnose this problem with out a scan tool is like looking at computer BIOS without a monitor,shooting in the dark.The door switches could be dirty,but if the dome light operates properly,the switches are working.

This is a dealer type problem,but you need to be able to give them helpful information for diagnoses.Intermitten problems are hard to find.

Customer: replied 5 years ago.

The intermittent problem now occurs every time I tunr the car off. Lasts for about 10 minutes and goes in cycles, horn beeps for 30 secodns off for a short time, beeps again 30 seconds, off etc over a 10 to 15 minute time frame.

 

Does this change how you would view the situation or just confirm that a dealer needs to look at this?

 

Expert:  John replied 5 years ago.
This would not change the diagnostic path .You need to see what the input & output sensors are reading in & out of the BCM(body control module).At this time you would also inspect for failure code in memory.

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