Stereo & Electronics - alarm sensor in door??? car wont start..1996
11-18-2007, 02:12 PM
my buddy is having a problem with his 1996 z28. Ever since he bought his car, he has had to unlock the drivers door with the key and hurry up and get in the car and put the ign key into the column and turn the key to the run position before the horn would start beeping. It has worked fine up until he started having problems with starting his car. I figured it was the key worn out and I ended up bypassing the PASS KEY using a resisiter. This worked for a while but now he just got his car back from the shop where they rebuilt his steering column and now the shop owner was telling him that the lock cylinder on his drivers door is worn out and it is not turning all the way to "disable the alarm". Can someone explain to me how this sensor inside the door works with the alarm system and can it be bypassed? The shop owner told him he has to buy a new cylinder and sensor unit from the dealer or he will not be able to start his car. Someone please explain this.
11-19-2007, 09:13 AM
The shop owner apparently doesn't have a clue what he's talking about. You have to disable the alarm system using the remote - using the key in the door will unlock the door but not disable the alarm. There is no sensor in the door cylinder.
Besides, the alarm has nothing to do with the car starting (unless it's an aftermarket alarm). The VATS (Pass Key) system is completely separate from the alarm system. The alarm system is called a Content Theft Deterrent System - it is intended to keep things inside the car from being stolen but has no connection to the starter or fuel systems.
11-19-2007, 09:55 AM
well the VATS system is completly disabled through the PCM and my buddy currently does not have the remote. He never did and now he is having issues with disabling the alartm that the car has. His issue is that once he unlocks the door with the key and jurries inside to turn the key to the run position, the horn will start going off and he is unable to start the car. there is nothing when turns the key. So, something is messed up somewhere either in the door or in the column. The strange thing is, the shop just rebuilt his column so it is brand new again. I am 100% sure the shop did a perfect job. This guy doesnt make mistakes. he is well educated on these cars. he said soemthing about the lock cylinder was not turning all the way to the unlock and he had to put a lot of turning pressure to get the door unlocked.
Now your saying that there is no sensor in the door at all that has anything to do with a factory theft system?
11-19-2007, 12:29 PM
Yes, that's exactly what I'm saying - there is no sensor in the door lock of any kind...alarm or otherwise. The only thing even remotely related to the alarm is the door-ajar switch that operates the courtesy lights and lets the BCM know when the door is opened (for the alarm, RAP circuit, etc.).
The horn blowing is part of the factory alarm system. The car not starting is something else because the factory alarm has nothing to do with starting the car. Sounds like he has more than one problem at the same time. It's possible that he has a bad BCM which has both the VATS and the alarm functions in it (along with courtesy lights, RAP circuit, audible chimes, and a bunch of other body circuits).
If it's not the BCM then the alarm is easy to fix - either buy a remote and program it to the car ($60 retail...considerably cheaper online), or program the alarm off using the instructions in the owner's manual and posted on this site.
11-19-2007, 07:46 PM
I took a better look inside the door today and there is a shock sensor inside the door that the rods for the door handle and door lock connect too. There is a 2 wire plug going to it. I think this is his problem. Sometimes if he unlocks the door with his key and gets in, the securuty light is on and when he goes to start it there is nothing. This only happens if the securuty light comes on. And it only does it half the times we try it. He does not have a remote for his car yet and we have tried disabling the unit per the directions but nothing changes, The security light will still come on and when it does, the car is dead in the water for 2 minutes until it resets itself. I dont know where to go from here. He is going to order a new sensor in the door and a new remote and we will see what happens.
11-19-2007, 09:38 PM
Good luck with that. The dealer will have a hard time looking up a non-existant sensor for the door. If the two wires you saw are connected to a small block on the door latch assembly then that is the door ajar switch. Once again, it has nothing to do with the security light on the dash or the car starting. But you go ahead and replace it.
11-20-2007, 01:26 PM
Ok, I got you on the switch in the door now. I was researching a bit and found this out. So, you where saying that he must have another problem somewhere else in the car? Where is a good place to start looking? You also mentioned that the securuty system has nothing to do with the car starting right? it seems the only time the car will not start is when the security light is on in the dash.
11-20-2007, 02:12 PM
You also mentioned that the securuty system has nothing to do with the car starting right? it seems the only time the car will not start is when the security light is on in the dash.Yes, that's correct. The indicator for the content theft deterrent system (the alarm) is a red LED on the top of the dash next to the defroster vent. The indicator for the VATS (vehicle anti-theft system) is the lighted word "Security" in the instrument cluster. When the security light goes on it indicates a problem with the Pass Key system and won't allow the car to start.
Ok, I got you on the switch in the door now. I was researching a bit and found this out. So, you where saying that he must have another problem somewhere else in the car? Where is a good place to start looking?The symptoms point to a problem with the VATS (Pass Key) security. Since you've already bypassed the system, we know it can't be the key or the ignition cylinder. That leaves us with the BCM (which controls the system) or something loose in the bypass. I'd check that the resistor you installed hasn't come loose first since it won't cost anything.
You can test if the BCM is the problem by manually grounding the starter relay control wire. If that solves the problem then you know the BCM is failing to provide that ground and is probably defective. The starter relay control wire is a yellow with black wire in the large blue connector at the BCM. There are two wires that color - you want the one that is between a blank spot and a gray wire, not the one that is near the end of the connector. You can find the same wire at the starter relay itself in junction box #2 under the hood on the left fenderwell.
That should get the car to start but it won't continue to run with the security light on because the BCM also controls the fuel enable circuit of the powertrain control module. So, if you find that bypassing the starter circuit in the BCM works then you should get a new BCM to take care of the problem.
11-20-2007, 02:48 PM
So even though the PASS KEY is disabled in the PCM, I would still need that resistor under the steering wheel? I had orignally installed it to try and cure a possible bad key problem. But, that problem is the same we are having now so I take it that the key was never worn out to begin with and that was the start of this coninuing problem. My buddy dropped the car off at the shop and the entire column was rebuilt and tightened up. There was something broken in there and the mechanic just replaced it and tightened everything up. You think he may have messed with something by accident? I would hate to suspect him of doing anything wrong. heis a very well educated GM instructor. He knows his shit when it comes to GM cars and trucks.
Also, I am not to familiar with this bypassing of the BCM. I dont want to fry anything on his car. What exactly must be done in order to see if the BCM is the culprit? You said to ground the wire, now do I do this while the car is off and then to start it because sometimes the car starts like it should and other times it dont. And if it is indeed a bad BCm, where can I pick one of these up at? Are they VIN specific?
11-20-2007, 03:20 PM
Sorry, I had assumed that you already installed a VATS bypass resistor. If you haven't then doing that would likely take care of the problem. Since resistors are so inexpensive, I would say that could be a good place to start. My suggestions about bypassing the BCM were based on the assumption that you had already installed a VATS bypass resistor - they aren't necessary otherwise.
Disabling Pass Key in the PCM only affects one of the two anti-theft measures that are implemented by the VATS in the BCM. When the wrong key is used, the BCM turns off the fuel enable signal to the PCM preventing the engine from running. But it also turns off the starter relay coil ground, preventing the car from starting. It does this directly without involving the PCM so that part can't be programmed out.
I wouldn't suspect the shop of doing anything wrong. It's likely that the contacts inside the ignition cylinder are worn and only providing intermittent contact. The only way to correct that is to replace the ignition cylinder. Or you can ignore it after installing a VATS bypass.
11-20-2007, 05:27 PM
if im not mistaken, the shop left the resisitor in. The guy did notice it and told my budy about it and I am pretty sure he left it alone. I will ask my buddy tonight though to be sure.