Alarm No Longer Arms With Key/Fob! Help!

[Eric S.]

My problem is that lately my car (1999 540/6) doesn't seem to want to lock the doors and arm the alarm with the key fob. This is intermittent, happening about 1/2 the time. My workaround for now is I simply insert the key into the driver's door lock and turn it to the right, which locks the doors and arms the alarm, signaled by the "beep" and flash of turn signals.

I asked my dealer service advisor and a tech who was nearby what could be the deal. They asked if I was getting any "false alarms". When I said no, they said that ruled out engine/hood pin switch failure (a common issue according to them), and so they both asserted that the Driver's side door lock actuator sounded faulty.

They maintained this theory despite my informing them that the door lock actuator works fine when I insert the key into the lock and turn. It's not like there's a mechanical connection there - turning that key makes the actuator pull down the little lock plunger. To my logic, there isn't anything wrong with the door lock actuator.

More points:

• The fob unlocks the car every time
• My wife has noticed the same thing with her key
• I replaced the batteries on both keys about a year ago as part of the Inspection II. My wife hardly uses her key, so I seriously doubt it's the battery in the fob.

So what could it be? Driver's door pin switch? If that were so, then shouldn't I be getting false alarms? I am afraid it's some kind of master "alarm module", but the dealer asserted that this was highly unlikely.

My research of previous posts doesn't point to any solid answers except to have the dealer troubleshoot it. In my case the minimum cost of that would be $100 for the diagnostic (possibly higher)...

Any theories?

[da_bull]

Since the key fob/alarm seems to be the only thing common to the problem, it seems to me that both the key fobs are bad (not likely) or the receiver portion of the alarm isnt recognizing the correct code coming from the fobs. I would assume the fobs are ok. When the receiver collects the proper signal it is supposed to perform a certain function (trunk,doors, etc). It seems to me something in the brain module is not doing its "process" once it receives the signal. They all come in through the same antenna, so if your unlock works fine EVERY time, then thats about all thats left.

So Regis, that's my final answer: D, the brain module

hope that helps...

[superdeadman]

how would the key lose its codes?!
the problem gotta be somethign else...
i dont know how the locks work but im' assuming there supposed to be some kind of reciever.. that gets the signal and lock/unlocks the doors
that might be a problem since your wifes key should have good battery and good key... batteries RARELY go bad in 6 months.. ESPECIALLY 2 batterues!

[Dirty_Tool]

Eric,
What does it do when you go to arm the alarm/lock doors with the key fob? Does it just do nothing? Does it give you three beeps?
DT

[Eric S.]

Originally Posted by Dirty_Tool

Eric,
What does it do when you go to arm the alarm/lock doors with the key fob? Does it just do nothing? Does it give you three beeps?
DT

Hi DT -

I am glad you responded. To answer your question: about 1/2 the time when using the fob to arm/lock, I'll get the ol' single beep and lights flash and all is well. The other 50% of the time, absolutely nothing happens. No beep, no nothing, no matter how close I am to the car. Then, when I use the direct door-lock-and-key-turn method, all locks go down and I get one beep and one flash, exactly as with the fob when it's working.

Again, note that using the fob to UNlock/disarm works 100% of the time.

[Dirty_Tool]

Eric,
if I had to take a guess off the top of my head I would guess a bad receiver module. On your model I believe this is incorporated into the antenna module located behind the LR C pillar trim on the interior. Once again this is just a guess. This is kind of an oddball problem you have. Good luck and any questions just ask.. you know where to get ahold of me

DT

[Baashar]

The same thing with my 97. Sometimes it will work sometimes it wont. Sometimes I have to press it like 20 times before it works and walk around the car. Usually as Im walking away Ill go to the trunk and lock it from there to arm it. Its not just your car, mine has the same problem.

[superdeadman]

eric and baashar (sorry, don't know your name)
if you both got e39s with older key fob (the key is not retracatble) try the following:
put up the actual metal part of the key to your chin and press unlock

your body will act as conductor... when i do it, it increases the range on which the fob works by about 1.5 times. so i'm thinking if both of you got bad recievers, maybe all they lack is reception, so better stronger signal may do the job

[billB]

I had a similar problem and it turned out to be the key itself.....I was able to unlock it but couldn't lock and arm.......the key had a bad contact under the bigger rounded button!

[Eric S.]

Originally Posted by billB

I had a similar problem and it turned out to be the key itself.....I was able to unlock it but couldn't lock and arm.......the key had a bad contact under the bigger rounded button!

Interesting. That's where I was headed with it until I checked and my wife's rarely used key displays the same symptoms.

I haven't yet researched how to re-initialize the key, but that sounds like it's worth trying. It'd be a free fix attempt, anyway...

[billB]

The way I fixed it was to take it a part.

[Baashar]

Im gonna replace the key anyways though, its a 150 dollar key though. it needs to be replaced, all the buttons are worn out and it looks bad

[nukeduster]

Even with disuse the batteries drain. Check the batteries, theyre 50 cents, before you check anything else. I have to replace batteries in alot of fobs every 12-24 months or so.

[Eric S.]

Good points about the batteries, but if it IS the battery, how come the problem is only with locking, not unlocking, and the symptoms are the same with both keys, which do not see equal use?

I appreciate the suggestions, just trying to work out the logic. The most logical part is that the battery is a mere $2 part so what the heck, why not try it?

[WardJ]

what the hell is fob. i cannot figure it out for the life of me.