C class immobiliser problem

[ianf7525]

I have a 1996 C class, which has just developed an immobiliser issue.

First that I knew about it, the car simply would not start. After then strugglingto lock/unlock the car with the remote I eventually came to the conclusion it needed new batteries. That done, the doors now lock/unlock but it would appear I cannot reset the immobiliser. Having contacted local MB dealer, I attempted to follow the reset procedure but either I am doing it incorrectly or I have been misinformed.
Has anyone else suffered the same problem and how did you resolve the issue?
Can anyone suggest the correct reset procedure?
Any help/advice would be greatly appreciated.

 

[Dec]

Sit in the unlocked car
Point remote at rear view mirror
Press button twice in quick succession…this will lock and unlock the car
Put key in ignition, within 30 seconds, and turn it to position 2… which is ignition on.

If that doesn’t cure the problem then it is possible that a transponder chip inside the key fob has become detached and is loose inside the key fob, it is tiny and should be glued to the location indicated by the Red arrow in picture below.
I’m only guessing that you have this transponder in your key but given that your car is 1996 it might.

Care is needed in opening the fob so as not to lose the transponder if it is loose?

Dec

 

[ianf7525]

Hi Dec

Thanks for your reply.

Tried the method you instructed but all that happens when I pit key into position 2 is s few dashboard lights come on very faintly, and a few seconds after that the red light on the rear view mirror flashes again as thought he alarm has been set.
How long am I supposed to leave key in position 2? and then do I just remove it from ignition or attempt to start the engine?

Also wanted to try looking at the transponder but I can't seem to be able to remove the cover. I can get to the batteries but can't get the rest off to see the transponder, is there some special knack required?
I'm afraid to break the key as it's the ony one Ive got.
Thanks again.

 

[Dec]

You should just be able to start straight away after key is turned to position 2, I think it is just the act of lock/unlock and the ignition being switched on within 30 seconds I think that’s all that matters.

If your getting a Red light then the car must be immobilised, does the Green light flash at any point when you unlock? A Green light, on its own, would mean the car should start.

“dashboard lights come on very faintly!" …sounds like a dead or poorly connected battery, check the battery terminals for tightness, particularly the additional, smaller, connected wires at the + Positive battery post.

The key fob is a prise apart/snap back together affair, like the battery compartment.
Open out the flip blade, in the grove where the blade lives (where coins are in picture) you will see a seam which when prised open with a sharp penknife will divide the shell into two equal halves along its lenth.
The Red lens and silver key part don’t divide, obviously.
Watch out for tiny bits falling on the floor.
See… http://forums.mercedesclub.org.uk/showthread.php?t=26888

Test your key as in bottom picture below, several times, you should always get the Red and the Blue/White light every time.
By the way, the batteries in the picture above, post #2 are installed the wrong way round.

Dec

Picture source… http://www.niallbrady.com/mycar/NEEDED.jpg

 

[ianf7525]

Dec

When I do the double press, the first press gets the red light flashing which closes the central locking, the second press then unlocks the car and the green light flashes. I insert the key and turn to position 2. Nothing happens for a few seconds and then the red light starts flashing on the mirror. So it appears to be turning the alarm/immobiliser off but still won't allow the car to start.

On some occassions whent he key is in the ignition I can hear a little pleep from the alarm as if it's arming itself.
I'm fearing a major problem and as we don't have a dealer where we live, and with the car not starting, it may be a job getting it to the dealer if it needs it.

I'm beginning to think someone has glued the two halves of the key together as I'm still unable to get further than the batteries.


Will check on the car battery, the connections and the charge in it later this afternoon.

 

[Dec]

That the red light, after you turned the key, shouldn’t be coming on… obviously. Is the alarm actually working ok?
Try;
Lock yourself in the car
Stay still for 30 seconds
Open a door/s
Alarm should be sounding… is it?

Dec

 

[ianf7525]

Alarm did not go off when I opened the door, just the alarm gave off a little bleep.

 

[Dec]

Did anything else happen to the centeral locking when the alarm gave off a little bleep. Did dooors lock perhaps?


Dec

Edit; What key fob/s do you have with that car?

 

[ianf7525]

No, just the bleep. Doors only lock when I press the button again. It just seems everything is (relatively) fine until I try to start it.

Finally got key open and eveything appears as it should (as per your photos).
Nothing missing, everything firmly attached.

I have noticed when I go through the button push procedure, the dash lights come on fine (clock, speedo etc) but when I put key in and turn to pos 2 the main lights go out and its just the oil, battery etc lights that come on but very dimly.

 

[Dec]

It all seems normal except for the word “dim” the shouldn’t be dim. When you turn an ignition normally all lights should light up for about 30? seconds so as to check that all warning bulbs are alive, all dash lights should then go out except for the battery/ABS until you start… so, going dim and a Red light flashing and a non-working alarm, what about keys, any in your possession for turning the alarm off?

Dec

 

[ianf7525]

Unfortunately the car only came with the one key.

 

[Dec]

If an alarm isn’t getting any power (even if it is switched off, i.e. disabled when you unlock), it thinks the car is under threat and so it re-arms itself, it would seem that you are unlocking the car ok and the turning on of the ignition key seems to be causing this fault and as the alarm is faulty so it’s the main suspect.

The vacuum pump, located to the right side of the boot, should be checked out as it would be involved with the alarm in that the alarm is armed when the doors have been locked by the vacuum pump, the doors would be locked before the alarm is armed, any corrosion/wet on the circuit board or the electrical connection plug pins should be looked out for.

How many wires go into the alarm siren… its under the bonnet I presume, try unplugging the siren.

Dec

 

[ianf7525]

Will try looking at the vacuum pump tomorrow and the siren. Thanks for all your help.

Ian.

 

[mandrake]

have you checked the battery yet ,as i think you may be having a battery problem . also did you do any work on the car prior to the problem you are having .

 

[ianf7525]

Hi Mandrake

I haven't done any work with the car prior to this happening. Recalling now the day this all started, it was pouring down with rain and I had been forced to go through an enormous pool of water at the side of the road. i parked the car for a few seconds, turning off the ignition but not locking the car with the remote, got back in and that's when it refused to start. I'm wondering now if water has got into some of the electrics???

Prior to that, and I don't know if all Mercs of this age are like it, if I turned the engie off and left the car (to fill up for example) without locking the doors and setting the alarm, when I got back in the engine would turn over but not start. I would then have to set the alarm (while still in the car) unset it, and then the car would start. Is this usual??

Many thanks

Ian

 

[bigasotonuk]

Prior to that, and I don't know if all Mercs of this age are like it, if I turned the engie off and left the car (to fill up for example) without locking the doors and setting the alarm, when I got back in the engine would turn over but not start. I would then have to set the alarm (while still in the car) unset it, and then the car would start. Is this usual??

Hi,
What you are describing is exactly how my C230K alarm works, there were a few different systems around this time(Scorpion alarm and Immobiliser combined, stand alone Scorpion alarm with MB Immobilser, stand alone Scorpion Immobilser.) Yours should be Scorpion alarm and Immobiliser combined.

 

[bigasotonuk]

After reading all of this post, I think you need to solve the issue of the "dim" ignition lights first, are you sure the battery is fully charged? check both connections at the battery, also check the main engine earth and the main 12V feed that comes through the floor pan in the passenger footwell.

 

[Sturge77]

dont know if it has been suggested but try disconnecting battery for 30 mins, worked for me! exactly same symptoms, eventually had to change key fob batterys

 

[Sturge77]

also merc man told me to disconnect alarm as MB alarms are generally the problem! mmm!

 

[mandrake]

this must be catching .i have now a problem .right i have changed the batts in the fob ,now the car is unlocked i sit in the car press fob twice put key in and turn to 2cd pos on ignition all dash lights up ok, and within a couple of seconds the red and green light in the mirror flash alternately . the car will still not start . also the central locking is not opperating i cannot lock the car any help please