C180 Sport 1996 immobiliser fault

Halkirk

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Hi all,
I have a problem with my merc C180 Sport immobiliser. The red and green led's in the door handle and mirror flash simultaneously whilst cranking and the engine won't start.

I bought it at auction and it would only start if the battery was disconnected then reconnected and the engine started within 15 seconds.

I've removed the dealer fitted alarm and immobiliser and reconnected all the diverted wiring to no avail. I was checking the rest of the system and it appears that the transponder ring around the ignition lock is missing!! (that's if i ever had one!!). There is a small black two pin switch on the outside of the ignition barrel with a two pin white plug with female spade terminals in it but I think that this is the ignition key lockout switch.

There's a small black two pin plug nearby with round female sockets in it but I can't find anything to plug it in to (hence thinking that the transponder is missing!!) There is a push fit black plastic ring around the lock with a chrome plastic insert but no wiring (and it's just thin plastic so not the transponder!)

Is my car supposed to have this transponder ring?, and if so will a ring from a breakers do as a replacement?, is the key coded to the ring or the ecu and just transmitted by the ring??

failing all of this can I bypass the factory immobiliser?

Sorry for the lengthy post but I'm at my wits end (and I'm an auto electrician!)
any help would be greatly appreciated thanks.
 

Dec

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First, is your key working properly… have you a spare?

Red and Green flashing simultaneously mean the key fob batteries need changing, if the Red and Green flashing alternatley then the immobiliser hasn’t disengaged so the car won’t start.

The ignition lock of a NON-TRANSPONDER ignition looks like the below picture, note there is no wire, if the key fob has a transponder inside it then the surround would have wires attached to the surround.

IGNb.jpg


The main suspect here would seem to be your key so test it as below.

KeyfobAndBatteries.jpg



Dec
Edit; pictures would be useful of all these plugs you mention and a shot of the ignition lock as well.
 
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Halkirk

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Thanks for the speedy reply Dec, I'll answer the questions as they come...
My key is working correctly, when I got the car it was the first thing I checked, on opening the fob I discovered that the batteries were in the wrong way around so I went to my local Autoparts and bought a new pair regardless. They installed them for me and checked them with a small tester that lit up when they pointed the key at it and pushed the button. When I got home I checked it myself with my phone camera and both the battery test and infra red are working. I don't have a spare key though!!

The Red and Green lights in the car are flashing alternately so I sat in the car and pointed the key at the mirror and pressed the button twice then put the key in the lock and turned the ignition on, at this point the mirror and door lights started flashing alternately again!! (bugger!!)

The ignition lock surround is exactly as the pictures you posted, I'll try to upload a couple of pics when I get home tonight

best regards Alex

PS the central locking doesn't work either from the key fob or the passenger door lock!!, it does work from the switch on the dash though so I'm sure it's not the pump.....

Don't know if that's relevant but!!!!
 
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Halkirk

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Hi Malcolm, thanks for the reply yes I looked there I have the 210 820 28 26 box, still can't get the key to turn off the flashing red and green lights though, any idea where the immobiliser control box is??, I can start the car if I disconnect the battery, reconnect and turn the ignition on within 15 seconds so I must be resetting something!!, if I can find out what I'm resetting then I could at least fit a relay in the battery power supply line to come on when I turn the ignition on!, that'd give me the use of the car until I can tie down the main problem.

best regards

Alex
 

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Not 100% on this but could be under the dash, Alex knows this better than me
 
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Hi Malcolm, probably on my way there shortly have all the boot linings out, the back seats, parcel shelf etc.....dash lower panels and plate in passenger footwell where the dealer immobiliser was....gonna get to the point soon where I have a naked car!!

regards
Alex
 

Dec

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The only time the Red and Green flash alternately is when the key is turned to position 2, which is ignition ON, if the key isn’t at position 2 then the lights wont flash alternately, at all.

It appears you don’t have the transponder and your key seems to be operating ok, as the car is new to you perhaps all these plugs you mention have some bearing on the problem.

Its relevant alright that the central locking is working from the dash switch, it should also be working from the key fob, the key fob seems to be ok so it would seem the fob signal is not being received or it is not being acted upon.

Below is the immobiliser on mine under front passenger side foot rest, don’t know if yours will be the same.

Dec
attachment.php
 
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Thanks Dec, I've seen that unit on the footplate in the passenger footwell, the green wire in plug A was cut and the dealer immobiliser connected there, I've since removed it and soldered the wire ends together. Just a thought at this point but I've read in one of the forum posts that a diode in the mirror can fail and give rise to alarm problems!, given that the receiver for the fob is in there could this kind of fault cause the problems I'm having? and if so is there a fix? would I be right in saying that the mirror houses the receiver for the central locking AND the immobiliser or are they one and the same?

best regards
Alex
 

Dec

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I don’t know much about the mirror or diode, you do seem to be sending a signal from the key ok, from there on it all seems to go wrong.

The receiver is in the mirror… my key wont work unless I’m pointing directly at the mirror … the mirror receiver might be a simple device that triggers whatever events unfold in the immobiliser, look at the PCB of the immobiliser and all the wires that come out of plug B, that seems to be where all the brains are housed.

Its an odd fault, what with the disconnection of the battery solving it for short periods of time, its going to be hard to track this fault down.

Dec
 

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The actual diode in the mirror that picks up the signal from the key could be at fault
 
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Halkirk

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Thanks Malcolm, any ideas which one?, I had a look through the DIY section in the hope that there was a couple of pics and a repair schematic, I'm pretty sore I read it in the forums somewhere but can't find it now.

Had a good look at my immobiliser circuit board too but can't see anything amiss!!

regards
Alex
 

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Normally a clear one is the pickup Diode, I cannot be more precise than that with out a lot of checking
 

Dec

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What about the alarm system in that car, has it been completely disabled/removed?

Dec
 
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Halkirk

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Yep, the dealer fitted alarm has been completely taken out and all the factory connections reinstated, gonna check the mirror and circuit board, I was hoping to find a patch to disable the factory immobiliser then fit a complete Toad system. Might just sort this out and make it reliable yet!!

regards

Alex
 

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Regarding a relay patch that you mentioned earlier, if you could determine which fuse, if removed, will have the same effect as a battery disconnect then you could put that fuse through a switch that’s wired into the cabin.

Dec
 
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Halkirk

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Thanks for all your help guys, I went to ebay and bought an immobiliser box and matched key fob, my c180 is a happy puppy again.
 


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