foxden

I have been searching the forums for a solution to my non functioning passenger seat. It does work very occasionally, and when it functions it does so flawlessly.

I was prepared to remove the power seat adjustment relay and resolder any bad joints but I can't find it. I looked under the hood where the fuses and relays are but no luck, nor in the trunk (took out carpet but no compartment below).

I do recall reading one post that said there were no relays - it was part of the control unit under the seat.

Help please. I have repaired poor solder joints before, but can't do it unless I identify the relay.

mrboca

There are no relays. You have the door control module at the passenger and driver sides which communicate with the ESA modules under the seats (ESA= Electrical seat adjustment module), The ESA modules have all the motor control and logic to drive them. It is possible that the interface cable to signal the controls between the door control and the ESA is not making a good connection. It could be a module problem too. It is hard to detect what is wrong when it is intermittent. You can unplug and replug the CAN bus connector under the passenger seat (the one with the brown and brown/red leads).

foxden

Thanks, I'll cease searching for the relay. I'll focus on the module and it's connectors under the seat.

foxden

The seat acts as though it isn't getting power, i.e. a blown fuse. But maybe 1 out of 100 times it will work perfectly with the door open or with the key turned - the seat controls all work as designed, up down, back and forth, headrest and back, and when it is dead, it's just dead, nothing works.

If there isn't a relay sending power to the unit when the door Is open or the key is turned then could I have a poorly connected fuse? If so, which ones exactly should I be focusing on?

Is there some way to verify voltage is getting to the module?

foxden

Not sure anyone is following this thread since I received few responses, but just in case. I have verified 12 volts going into the module under the seat, now I am trying to determine if it's the module or door switch.. When it works it works perfectly, its all or nothing with the seat.

mrboca

Attached is the schematic diagram for the power seats. Have a look at them and let me know if you have any questions . Maybe you need to check the fuse that goes to the door control unit.

Honestly, if you want better support, go to Benzword.org and post it under W210 forum there. This site seems to be very unresponsive.

foxden

Thanks for the info. I am sure it's exactly what I need to track down the problem. Only trouble is I really can't understand it. I'll have to get one of my electronic buddies to help translate. I am more of a nuts and bolts person.

mrboca

Alright the chances are, you have a bad connection or pinched cabling where the right door meets the car body. It is marked on the diagrams as X35/42. That is where the terminal for the door module, and signaling to the seat electronics go to. Since the passenger seat works from time to time, I think the fuse is OK (under the rear seat fuse panel). So it is likely a corroded connection / or pinched wire which makes a contact from time to time. You can open the door at certain point it may make a contact. Check the door electrics connection point near the hinge.

foxden

I'll start looking at the hinge and see if moving the door while open triggers it to work. I agree that the fuses must be good as when it works it does so perfectly.
Thanks.

foxden

I am not sure if that's it or not. Intermittent issues drive me crazy. I opened the car door, checked to see if seats worked-they did not. I squeezed the boot between the door and the car body and tried again. They worked fine. Came out and tried it again-this time they wouldn't work. Not sure if there is a poor connection there or merely a coincidence.

I am not sure how to access any connector inside the boot. It looks tight and waterproof, but in Florida with the salt water so close, corrosion can occur.

I continue my search. Thanks for the guidance. Happy holidays, too.

mrboca

Happy Holidays I was looking for the place for X35/42 but I could not locate the picture to show how to access it. I believe it is behind the right front sill at the passenger door frame. A black connector with 4 wires (2 for can bus, two for power). I would first check the grounding (right front seat cross member). If the ground is not good, you may have intermittent problems too. You should check this prior to removing the sill.

Also I believe your right mirror is also controlled by the door module in the door through the can bus. If your right mirror adjustment is not working this would also indicate that the door module is not getting power / can bus signaling.

foxden

The mirror works fine. Auto adjusts when in reverse, etc. The lights in the door switch illuminate, too, when headlights are on. I will check the ground as you suggest and look for the connector.

I sure appreciate the guidance. Thanks.

mrboca

I believe for your 1998 model year the mirror control is done by signaling between the ddor control module and the lower console control unit (where the mirror switch is), then the door control unit directly controls the mirror. If the mirror control works and the power seat is not, and the door control switches are lit (when the headlights are on), that mean the door control module and the switches work OK. So the problem area seems to be the grounding of the ESA (seat cross-member), powering of the ESA (two fuses under the rear seat (25 amp each), two power wires coming to the ESA connector, and CAN bus connection to the ESA (brown and brown/ red wires).. You can just disconnect and re-connect the above connectors (with the key out). Do not touch the seat occupancy presence sensor connector.

Without a service scanner like SDS that can talk to each module and pinpoint the module that is not responding, it takes time and effort to solve the problems like this (of intermittent nature).

foxden

I really appreciate your efforts in this issue. I hope you aren't getting as obsessed as I am trying to solve this. I did check voltage on pins of the locking connector and recall a couple pins reading 12 v. That's why I figured the unit under the seat gets power. I will look for the ground and check that.

Who has the scanner you refer to. Only MB dealers?

If I do get this solved I will post back so at the very least you'll get the feeling of closure.

Thanks again.

foxden

Me again. Hate to admit it but I can't find any ground wire you refer to. I looked under the seat.

Pulled and inspected each connector on the passenger seat module. All were clean and secure. It did work after I plugged the locking one back in. 15 minutes later it didn't work and unplugging and re plugging didn't make it work.