W211 CAN from seat module

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ayvo

Active Member
Joined
Oct 19, 2019
Messages
135
Location
UK
Car
E320 CDI
I have a 2004 E320 cdi which recently developed a serious electrical fault, after replacing a rear sam I pinpointed that unplugging the big connector from the seat control module (the one labelled CAN on the module) makes everything work perfectly as it should other than the passanger seat controls etc not working ofc.. I bought and replaced the module thinking it was the module but still the same fault, once I plug the big can connector at the front into that module, SRS light comes on, says srs defective, ESP defective, radiator fan spins on full speed constantly, no electronic in the entire car works and the red battery sign comes up saying visit workshop.. the car goes absolutely crazy.. what should I check next?
 
The fault will likely be in whatever component(s) are successfully isolated by you unplugging the connector - the actual seat itself maybe? Given the multiple electrical warnings you get, my suggestion would be the CAN wiring in the isolated component(s), likely damaged insulation and the wire core earthing on the seat frame or similar.

Think of the CAN network in the car as one large communication loop going via all modules on the car (overly simplified admittedly). A fault in the CAN communication on one component affects many other components as the whole loop sees (and is confused by) the faulty communication.

Martin.
 
What a great car had it nearly a year but by Christ can it be annoying with these little electrical glitches well assume they are electrical glitches or senser issues which come and go leaving you wondering why, The latest one popped out of the blue jumped in the car yesterday morning and this morning and on both occasions once I’ve started up and pulled away the driver seat starts acting up automatically goes down I press to go up it goes down then by the time I’ve got to the station some 5 minutes away it starts operating correctly leaving me scratching my head thinking what the hell can it be please tell me someone as had the same experience. Once it stops everything works as it should, is it one of Mercedes infinite sensers
 
Odd faults like this can be caused by a low or defective battery, especially if only being used for short journeys. I would check the voltages as a starting point..
 
The fault will likely be in whatever component(s) are successfully isolated by you unplugging the connector - the actual seat itself maybe? Given the multiple electrical warnings you get, my suggestion would be the CAN wiring in the isolated component(s), likely damaged insulation and the wire core earthing on the seat frame or similar.

Think of the CAN network in the car as one large communication loop going via all modules on the car (overly simplified admittedly). A fault in the CAN communication on one component affects many other components as the whole loop sees (and is confused by) the faulty communication.

Martin.
Thanks Martin will certainly have it tested like I said nothing make sense why it would start to behave the way it is
 

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