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Stan, Mercedes Technician
Category: Mercedes
Satisfied Customers: 3526
Experience:  Technical support engineer
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C220: to the receiver (in the mirror assembly)..doors..cabin..driven

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1996 C220 - Immobiliser problems - really weird one this: The immobiliser only "talks" to the receiver (in the mirror assembly) when the doors are opened and closed until eventaully the cabin light illuminates. Then the immobiliser button can be pressed and lights illuminate either green or red - like it should. Car can then be driven. When you stop, get out, and try to start again, the motor will turn over but wont fire up. The afforementioned procedure has to be repeated. And only when the cabin lights decide to turn themselves on, will the immboliser allow the car to be started!! I have tried different batteries (in car) as well - same result. The eratic behaviour of the cabin lights should mean something! Also last night - ignition turned off completely and engine cold, the radiator fan comes on for a few seconds and switches off again! Otherwise the car is squeaky clean, no accidents and not butchered.


Basically, the immobilizer consists of 3 main units: IFZ immobilizer/ signal receiver module, PSE- pneumatic central locking module and engine control unit.

IFZ unit receives key signals through receiver in the mirror and transponder signal pickup coil around the steering lock. There is a transponder chip in each key fob.


Once the remote is operated, valid signal is picked up and green light is operated in the mirror and PSE module receives command from IFZ to unlock the doors. Once you open the door- PSE turns on interior lights. When the key is inserted, valid transponder signal is picked up by IFZ coil and it gives the engine control unit permission to start.


It seems to me that at the moment we have a problem with PSE control module. It is located on the right side wall of the trunk behind the paneling. I suggest to pull it out to check the plugs and internals for moisture/oxidation. This can cause some of the weird behavior.


Another pre-check would be to remove and resolder overvoltage protection relay. It supplies voltage to many electronic units and is prone to have dry/cold solders inside.

It is located under the bonnet, on the right side next to engine and ABS control units.


Please check these 2 things first, and let me know what you find and if this will solve the issues. I will be glad to help you further with this.


Best Regards,


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