Ok, first of all, roll the driver's window down, hop out of the car, use the power lock button on the door to lock the doors, close the door, then wait for at least a minute. The anti-theft system will arm if you have it. Now reach inside and open the door with the inside handle. If the horn starts blowing and some lights start flashing, you have the anti-theft system. This is real important to know when it comes to replacing the Body Computer or the Engine Computer. If you have the anti-theft system, you can use any computer from the salvage yard, but from then on, that computer will only work on another car that also has the anti-theft system. DO NOT borrow a friend's computer if his car doesn't have the anti-theft system.
Both computers have anti-theft programming that can not be undone. If your car does not have the anti-theft system, you must find a used computer from a donor car that also did not have anti-theft, and that can be impossible to find out from the salvage yard since there's no easy way to tell unless the car was running when it was brought in. Even then, they might not have bothered to find out.
When you install either the Body Computer or the Engine Computer with anti-theft programming into your car without anti-theft, the new computer will teach it to the other one. A Body Computer will teach it to the Engine Computer or a replacement Engine Computer will teach it to the Body Computer. At that point the car will not start because both computers are waiting for the disarm signal that's never coming. Both computers will have to be replaced at the same time. If you just replace one of them, it will immediately learn the anti-theft programming from the other one as soon as the ignition switch is turned on.
If you buy a remanufactured Body Computer from the dealer, it will come without the anti-theft programming. It will work in any car as soon as it is installed and will self-program itself for anti-theft only if the system is on the car, when it learns it from the Engine Computer.
I just wanted to get all of that out of the way in case you do need to replace the Body Computer, (Body Control Module) ( BCM).
Is it possible a neighbor has a similar car with a remote key fob? It's rare but not unheard of when the trunk pops open for no reason.
When the horn blows by itself, does it pulse about once per second or does it blow steady? Pulsing is a sign the anti-theft system was activated, but if it stays on steady, suspect a clock spring under the steering wheel that is beginning to break. It is a wound-up ribbon cable that makes a solid electrical connection to the air bag, horn switch, and cruise control switches. Usually those three things will stop working, one by one, but it is possible for the ribbon cable to unravel and the horn circuit grounds out the same as the horn switch would do. If the clock spring is the cause, turning the steering wheel is likely to make the horn turn off.
I've never run into a defective remote trunk switch but given how common it is for plastic parts to warp, you might try unplugging the switch as a test. If the trunk still pops on it's own, at least you'll know it's not due to the switch. Also, try popping the trunk while the transmission is in drive or reverse. I can't remember about cars, but I know on minivans the lift gate will not pop unless it's in park or neutral. If your car is the same way, and the trunk pops on its own while you're driving, that would rule out the switch and would point strongly toward the Body Computer.
Thursday, May 6th, 2010 AT 4:08 AM