'94 R129 - Alarm/Immobiliser problem.

[E55BOF]

Oh B****r! NOW I know why the Selca immobiliser is fitted.

I got my nice new infra-red flip key from MB, and all was well - until the alarm/immobiliser started to play up. The infra-red remote works most of the time, but not always; not a problem if I can't lock the car - I can use the ordinary key, and there's the Selca immobiliser to provide a degree of security. The vacuum C/L is working perfectly, but is not activated by the remote

It doesn't seem to make any difference whether the car is level or a little nose-down on a slope, so probably it's not the anti - tow switch. I've tried re-synchronising the fob; no change. The red tell-tale in the fob comes on every time.

However, when I can't unlock it with the fob, then of course I cannot un-immobilise it either, and that's the situation now. I can hope the system decides to play again (which it very soon has the two or three times the problem has occurred before), but at the moment it's completely refusing to do so.

Once (assuming it does...) it comes back, I can disarm the system, then just use the key until I can fix it/get it fixed. If it doesn't come back, can anyone tell me how to bypass the alarm/immobiliser completely so I can start and drive the car?

Are there any other checks I can make to try to diagnose the problem before I start throwing money at the car (again...)?

 

[RichardF]

Try removing the alarm module and re-seating with some contact cleaner.

 

[E55BOF]

Could do, if I knew where it was... It is the ATA module, I take it?

 

[RichardF]

ATA module is in the boot down by the battery.
Have you tried pointing the remote @ the boot and passenger door?
You also have a fuse IIRC it's number 5 in the boot mounted fuse box.

 

[E55BOF]

Thank you, Richard. The remote does not operate through any of the door receivers, which I think suggests the problem is more likely to be central; the fuse, or in or near the module.

The mechanical lock for the boot does not open it manually when the central locking is locked, so I cannot get into the boot to check fuse or module...

Fingers crossed it will decide to play again sometime soon...

 

[RichardF]

If the C/L is working unlock it from the drivers the door, alarm will go off, open boot and whip off the battery lead quickly before it winds up the neighbours.

 

[E55BOF]

I don't know whether it provides a further clue to the problem, but the C/L was disabled as well. (I say 'was' because the system eventually came back briefly, and I opened the car with the fob. The C/L works perfectly well with the key from either door, so I won't be using the infra-red to lock the car, and thus arm the alarm/immobiliser, until it's sorted.

Does the C/L send a signal to the ATA, or is it the other way around? Does the C/L have a separate ECU, or is it all part of the pump unit, do you know?

The fuse is fine. I'll clean up the module contacts on Saturday, then go through a phase of locking the car only with the key, and unlocking it with the infra-red, and see if it carries on working. Wish me luck...

 

[RichardF]

C/L and ATA control units are mounted just above the C/L pump. I'm not sure how they communicate.
The main earth point is up there as well, strangely the C/L pump seems to also use the earth point on the other side of the boot behind the left hand panel

Mine would not always disarm/arm with the I/R, although it'd operate the locking ok. Cleaning the pins on the ATA module resolved this.

In the boot
Fuse 5: ATA (I think if you remove this you'll be able to lock the car with the IR but not arm the alarm/immobiliser)
Fuse 6: Boot light, C/L, I/R, antenna.

You can read the codes to see if they shed any light on anything. Could it be to do with the after market alarm you removed?

And lastly it'd be worth sorting the mechanical lock for the boot, if the C/L fails you're in a whole world of pain trying to access the pump etc.

 

[E55BOF]

Thank you for that. I'll give them both a good blast with contact cleaner, then see how it goes thereafter. If that doesn't work, a trip to WG MB will be next to get a STAR on it.

 

[RichardF]

You don't need star for this, build your self a blink code reader. It costs pennies and will pay for itself over and over again.

 

[E55BOF]

I started with the white 'black box' behind the ATA module; it's not the C/L module, as alarm/immobiliser and C/L were both unaffected, as I found out after unplugging it, but I cleaned up the contacts anyway since I had it apart.

On to the ATA module ( the black 'black box'); cleaned up the contacts, and Bingo! it works again. I don't trust it yet, though; I'll stick with locking the car only with the key, and unlocking it with the infra-red, for a month or so and see how it goes.

I notice that the passenger door IR receiver only functions when it feels like it, but that's another problem. I'll get round to it eventually.

 

[E55BOF]

It's bloody doing it again....

It was fine for a while, locking with the key and unlocking with the IR fob; no problems. So I got cocky, and locked it with the IR too. First time, no problem; second time, no unlock.

Time to make that blink code reader and see if it can pull any fault codes to help locate the problem.