Drivers Side Seat and Steering Wheel Adjustment Issues

[owenj99]

I've been working for a while now trying to fix the drivers side seat and steering wheel adjustments. The seat bottom rear up/down adjustment isn't working, the headrest adjustment isn't working and the steering wheel will not move in/out. I have tested all the motors and they all work. After that, I took out the seat and removed the control module and found that all relays seems to be actuating properly, but are not delivering 12V to the respective trouble motors. I figured the actual relays that flip the current between positive and negative to reverse the direction must be bad. I finally found a tested module on eBay matching my part number and plugged it in... all functions work except the same 3 from before. At this point I'm pretty much stumped because I do not understand how the module could not work because they are receiving the 5v input signal from the switch, and the relays appear to be actuating properly but the power never makes it out of the module. When I put 12V to the connectors running to the motors all functions work, so I do not think it is an issue with the wiring from the module to motors.

Has anyone else had issues similar to this?
The module part number is 129-820-01-26. There is another smaller number under it reading 3-137-211-010.

Thanks in advance!

Owen

 

[gerryvz]

Just a shot in the dark -- have you checked all of your fuses in the fuse box?

Specifically looking at fuses C, E and F.

 

[owenj99]

Just a shot in the dark -- have you checked all of your fuses in the fuse box?

Yes, I checked all the fuses a few weeks ago, but the seat wasn't working when I bought the car. It's strange because you can hear and see the relay actuate and it is getting power and signal from the switch but it seems like it just doesn't make its way through the module.. I guess that can't be the case now because the other module did exactly the same thing...

 

[gerryvz]

OK, well, please look at the following:

In addition to the three fuses mentioned above..... (rotate all of them in their sockets). In particular please focus on fuses E and F.

Relay "A" -- in the relay panel behind the fusebox, underhood, driver's side. Relay "A" (K5) controls the seat adjustment. Replace this relay with a known-good relay. It's the furthest one back under the windshield on the passenger side of the relay box. PITA to get at.

You obviously know there is a power seat control module under each seat, with the driver's module having the "memory" function on the US-spec cars.

I have attached the factory wiring diagrams for the seat adjustment + steering adjustment systems. One with memory, the other without memory.

 

[owenj99]

I will check them out and get back to you. Thanks for the quick response and the help!

 

[gerryvz]

Make sure you check out all of the dependencies in the system -- the door switches, and so forth.

 

[owenj99]

funny you say that, I have found that the drivers side seat switch only operates with the passenger side door open when the car is off. The dome light and such also does not come on when the drivers door opens. A lot of strange electrical stuff with this car but I always chalked it up to the police systems being added. They did some very strange stuff with some of the wiring for the systems including adding a secondary procedure where you must unlock the passenger door to disarm the immobilizer. I guess I will try and figure out why the door switch doesn't work next.

 

[gsxr]

Have you tried a different seat switch in the door? Most of the time I've found the switch is at fault, not the motors or control unit under the seat.

Also, there is a diode buried in the back of the fuse compartment (with the relays) which can affect seat operation. I can't remember details offhand though, I haven't run into a problem with this diode in probably 10+ years.

BTW - if the alarm system (immobilizer / starter disable) will only will turn off if you unlock from the passenger door, the driver lock switches may be bad. You can disable the entire alarm system if desired.

What year/model are you working on?

 

[owenj99]

I've been tempted to just put a new door switch in anyways to remove potential confusion with all of this. I believe the immobilizer has been modified intentionally as a few law enforcement friends have told me that is standard for police cars. Could also just be a lock issue though... It is a 1994 E500. I'm planning on taking a look at the relays and fuses that Gerry mentioned this evening. I will also look for that diode in the fuse box when i'm in there. I will keep you guys posted with what I find. Thanks again!

 

[gerryvz]

You need to consider both the door-pin switches, as well as the seat switches in the doors. Just wanted to clarify.

 

[TerryA]

Have you tried a different seat switch in the door? Most of the time I've found the switch is at fault, not the motors or control unit under the seat.

Also, there is a diode buried in the back of the fuse compartment (with the relays) which can affect seat operation. I can't remember details offhand though, I haven't run into a problem with this diode in probably 10+ years.

BTW - if the alarm system (immobilizer / starter disable) will only will turn off if you unlock from the passenger door, the driver lock switches may be bad. You can disable the entire alarm system if desired.

What year/model are you working on?

@gsxr,

Funny you should mention the seat switch in the door. In the past my seat has acted up (and still does I’m sure). Anyway I bought a brand new door switch only to still have the same problems.

The issue is which ever way you push the seat to go, it does the opposite. What’s funny about this I’ve had my car into a Indy Tech who is very tall and has to adjust the seat so he can drive it. Whenever I get the car back the seat works properly for a while.

He’s never told me what he does to make it work. I haven’t been back to him in the last few years for any work but if I do go back I’ll press him for an answer.

 

[owenj99]

Hey guys,

I've been messing with the 500 for a while now trying to figure this out. I have pretty much narrowed it down to a ground issue somewhere near the drivers door. The door switch (for the dome light) functions properly, but the lights only come on if you open one of the other 3 doors, all convenience relays, diodes, fuses, etc. were checked, and all fuses were replaced with the good ceramic ones but those trouble functions still do not work for the seat, which I suspect it is related to that section of the module not getting ground as the module gets 2 power in and 2 ground in with both powers showing ~12.7V to 12.9V.

I have taken somewhat of a break from the messing with the ground issues and put everything back together last week so I can use the car (3 months of sitting isn't good for anything). I plan on pulling off the drivers door panel soon to check the wiring at the hinge as I hear the wires can get worn causing them to break or short in the door panel/hinge area.

Thanks again for all the help with everything!

Owen

 

[owenj99]

After a long time researching this issue, I ended up finding from a thread on MBWorld that a relay behind the instrument cluster that controls the dome lights and other features. I *THINK* it was called the N70 relay if I remember correctly. It mounts to a small bracket with two 10mm bolts way back behind the cluster and holds two relays. I replaced the N70? relay with a used part from eBay (about $35, part number 004 545 07 32) and reassembled only to find that everything worked as it should! Apparently, if you short the door switch it causes this relay to pop. I guess at some point, maybe during the police light installation or something the switch must have been shorted.

Thanks again to all for the help, and I hope this helps someone else too!

 

[LWB250]

Covered in a thread I wrote some time ago:

No Courtesy and Puddle Light for Driver's Door? | Electrical, CAN and Wiring

Glad you sorted it out. That relay is a real PITA to get to, isn't it?

Dan

 

[owenj99]

Covered in a thread I wrote some time ago:

No Courtesy and Puddle Light for Driver's Door? | Electrical, CAN and Wiring

Glad you sorted it out. That relay is a real PITA to get to, isn't it?

Dan

Ah sorry, could have sworn I saw it somewhere else. My bad. It wasn't too bad to get to. A series of long extensions on a 1/4" drive and it was out in about two or three minutes after removing the cluster. Resembling took a few minutes more are I was trying to be very careful about not dropping the nuts behind the dash.

 

[LWB250]

Ah sorry, could have sworn I saw it somewhere else. My bad. It wasn't too bad to get to. A series of long extensions on a 1/4" drive and it was out in about two or three minutes after removing the cluster. Resembling took a few minutes more are I was trying to be very careful about not dropping the nuts behind the dash.

It's all a matter of search terms/nomenclature. The difference between "courtesy" and "dome" lights.... Sorry you didn't see it. It is an obscure issue.

Dan