W202 - Strange Key Bahaviour

[Grahamcol]

I've had my 1996 W202 C200 (pre facelift) for 7 years now and it has been a great car. Just lately, however, the alarm (actually the 2 main keys, I think) has started doing something odd. Long story short, if I alarm and disarm using the flat "emergency" fob all is well. However, if I use either of the main keys, I very often get a situation where the alarm will not arm (if disarmed) or will not disarm (if alarmed). Whenever this happens the red led's in the mirror flash for about 40 seconds - together, if I remember correctly. The c/locking works every time though. I've put new batteries in and done a re-sync etc, all to no avail. As I said, if I use the flat emergency key it all works fine 100% of the time. Could it be the two main keys are both in need of replacement ?

 

[Dec]

Could you describe what you mean by the flat "emergency" fob and the main keys?

Do the Red and Green LEDs in the mirror flash together or alternately?

Dec

 

[Grahamcol]

Hi Dec,
The car came supplied with two flip keys containing key blade and just the single largish button used to open / close (via infra red). Also there is the credit card style infra red remote containing a pull out blade. The credit card style remote works fine but both of the flip keys makes the alarm "play up" fairly frequently but not all of the time.
When it plays up I think both green & red led's flash together. I think they flash alternately if the batteries need replacement. In any case I've got new batteries in all of the keys so I can't see it being batteries.
Thanks.
Graham

 

[Dec]

Do the hazard lights flash, and in what sequence do the flash when you lock or unlock the car with the credit car remote?
I’m curious to know why you are using the credit card key as it’s for emergency use, that is to say you would use it only if the flip out key failed to work.

If the Red and Green LEDs flash, alternately, for about 30 seconds when the ignition key is turned to position two (position two is ignition ON) then the immobiliser has not been disabled so the car wont start.

If the Red and green LEDs flash together when the you lock or unlock the car then the remote batteries need to be replaced.

In what way does the alarm "play up" is it sounding off when it shouldn’t? or is the car ever refusing to star?

Dec

 

[Grahamcol]

The hazards flash normally. i.e. once to arm and twice to disarm. No changes there at all. I started to use the emergency key because the two flip keys will not allow the alarm to arm / disarm normally. As I said before, I've changed batteries, done re-sync etc. and it makes no difference. I simply do not understand it. The ONLY thing I can think of is that both flip keys are somehow faulty.
Thanks for your input by the way.

 

[Dec]

Try LOCKING yourself inside the car using the CREDIT CARD key, wait a minute, without moving, and then try to start the engine… what happens, does the alarm go off, will the car start?
If the alarm doesn’t go off then try opening a door/s and or bonnet. Worth checking the door, boot and bonnet push pins to make sure the are working properly, particularly the bonnet pin switch.

I’m just thinking that either both flip out keys are faulty or the alarm is faulty AND the credit card key doesn’t have any authority over the alarm and all it does is lock/unlock the car and that’s why it always works… just a thought.

You could also try unplugging the alarm siren to see what happens with the fault, the alarm might go off when the siren is unplugged.
.
What does the alarm siren look like?

Dec

 

[Grahamcol]

Hi Dec (again),
I will try what you've said when I have access to the car. I'm actually using my "other" 202 at present. However, I'm pretty sure the emergency key has full authority over the alarm. My alarm siren doesn't look like any of the ones in your pictures. It's black and has a key hole at the back to turn it off.
Thanks once more.

 

[Dec]

If you have possession of the key for the siren then it will turn off the whole alarm system, it would be interesting to see what happens with the alarm system switched off, the car should still lock/unlock and start.

Dec

 

[Marku]

The keys can and do go wrong. Had trouble with one when the car was only two years old. Electronics started acting up and then one day got out leaving the key in the ignition and the car locked me out. MB dealer took it in and did all sorts of test and finally decided it was the key. Changed it and every thing was fine.

 

[Grahamcol]

Thanks Mark. Yes, it seems to me that in my case it can only be the key that's at fault.

 

[Grahamcol]

Update.
I'm 95% sure it is indeed both main keys. Although there are new batteries in both, I often get a situation where upon pressing the centre button and holding it, the red "check" light doesn't light up. That's despite new batteries. In this situation the key will operate the central locking and not the alarm, also both red and green mirror lights will flash together. As I said before, I never get this problem using the emergency infra red remote.
So, it's the keys. I'm not convinced the batteries always make good contact with the contact pins on the key itself. This might be part of the problem. On the other hand, maybe the keys have become intermittently faulty after 17 years / 145k miles.
My proposed course of action is to "mess" around with the batteries / contacts yet again. However, if I cannot get either key to work reliably, then I will have to consider purchasing at least 1 new key. I'm reluctant to do this, obviously, due to the ridiculous cost at MB, although I believe there's a company in Birmingham that's able to supply MB keys at a slighly reduced charge.
Thanks to the forum and in particular to Dec.

 

[Dec]

If your key ever fails the test above then its possibly the tactile switch inside the key has damaged legs or the switch itself needs to be replaced or the battery contacts on the PCB are a bit loose.
You might be better off to get someone with experience in electronic repair (TV/phone repair shop) if you lack the expertise yourself.

The key, when observed through a digital camera should look like what you see in the video below, one brief press produces a blue/white light or a continuous press of the button produces a red light after 1 second and a continious stream of light as long as you keep the button pressed.



Dec
[YOUTUBE]zQhwvjw29NA[/YOUTUBE]
[YOUTUBE]lCqfivH9-Dg&feature=player_embedded[/YOUTUBE]

 

[bennesspipers]

Im fed up of my 202s alarm/immobilisers antics, im taking it to Ian Walker in less than 2 weeks, he reckons he can disconnect the whole sorry bunch of tricks. Last week it commenced another round of its games which made the car unstartable for 3 hours.