Weird electrical problems- '05 CDI - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 09-19-2018, 11:40 PM

I have the seats out of the CDI for upholstery. I got the passenger side back, and after installing it and plugging in all the cables, the seat won't respond to any of the controls. I have a temporary driver seat (from my parts car) so the car can be driven. Also, the steering column control does not work, and the steering wheel is in the lower most position. It is hard to drive like this. I checked all the fuses behind the cover on the left side of the dash, and there is power on all of them. F29 (7.5 amp) should be for the steering column module. Since I know there is power from the fuses for the seats and steering column, I can assume these accessories should work. However, they don't. Electrical systems are my weakest auto repair ability, so I am begging for help here! If there is a test or procedure I can do, I'm all ears. Thanks, Rich

jay_bob · #2 09-20-2018, 07:14 AM

Remember everything on the interior of the newer cars (W210 and up) is controlled in one way or another by CAN bus.

If you have a diagnostic computer it should be able to see which modules are not participating. Also you have to check for sensor errors in the seat motors.

In order to move the seat back, the following has to happen:
You push the switch that slides the seat back
The door control module reads the switch movement
The door control module sends out a CAN message “move the seat back”
The seat control module listens out for the CAN messages involving that seat, amongst all the other traffic on the bus.
When the seat control module hears the message “move the seat back”, first it checks its known position, and also evaluates where the rest of the seat elements are known to be (from the feedback encoders on each seat motor) to know whether it’s safe to move.
Only now does the seat control module actually put voltage to the motor to move the seat.

I have first hand experience with this on my W210. The drivers headrest would randomly stop working. Turns out the position encoder in the headrest up/down motor would stop responding intermittently. When the seat controller lost its position information on the head rest, it threw a code, and locked out any further movement of the head restraint until it was reset using HHT emulator in Xentry. Replaced it with an encoder/motor assembly from the JY and it’s working as it should again.

Another one. I had on that same W210 a failing left rear door window motor with integrated controller. It would report CAN bus errors and one line of the CAN bus shorted to +. Once I disconnected the CAN bus lines one by one at the junction I was able to determine that the CAN bus fault was being caused by that door motor. So I went to the JY and got a left rear window motor. Well when I opened up the door on the JY car the regulator had failed (no surprise) and the cable was all balled up around the spindle. Got the motor out, got home, and installed it on my car. Tried running the window up and down with the new motor but it would only go up and not down. So I got the computer connected and turns out the controller had sensed the jam and inhibited the motor from running down anymore. Once I cleared that code the motor ran both ways.

Long story short is that it’s pretty much impossible to troubleshoot one of these cars without a computer. But once you have the computer it will lead you right to the problem.

97 SL320 · #3 09-20-2018, 08:59 AM

I'm thinking he turned the key on with the seat out / unplugged, this would likely throw a code and brick the system.

ROLLGUY · #4 09-20-2018, 06:53 PM

Quote:

Originally Posted by 97 SL320

I'm thinking he turned the key on with the seat out / unplugged, this would likely throw a code and brick the system.

What do you mean by "brick the system"?
Yes, in fact the car was moved around the yard with the passenger seat out (at the upholstery shop). When the seat was installed again, it would not move. Then the driver seat went to the shop, and one from my parts car was bolted in. The two seat controllers were not compatible ('03 seat in an '05), so I had to hotwire the motor to move the seat to get all four bolts in.

ROLLGUY · #5 09-20-2018, 06:55 PM

Quote:

Originally Posted by jay_bob

Remember everything on the interior of the newer cars (W210 and up) is controlled in one way or another by CAN bus.

If you have a diagnostic computer it should be able to see which modules are not participating. Also you have to check for sensor errors in the seat motors.

In order to move the seat back, the following has to happen:
You push the switch that slides the seat back
The door control module reads the switch movement
The door control module sends out a CAN message “move the seat back”
The seat control module listens out for the CAN messages involving that seat, amongst all the other traffic on the bus.
When the seat control module hears the message “move the seat back”, first it checks its known position, and also evaluates where the rest of the seat elements are known to be (from the feedback encoders on each seat motor) to know whether it’s safe to move.
Only now does the seat control module actually put voltage to the motor to move the seat.

I have first hand experience with this on my W210. The drivers headrest would randomly stop working. Turns out the position encoder in the headrest up/down motor would stop responding intermittently. When the seat controller lost its position information on the head rest, it threw a code, and locked out any further movement of the head restraint until it was reset using HHT emulator in Xentry. Replaced it with an encoder/motor assembly from the JY and it’s working as it should again.

Another one. I had on that same W210 a failing left rear door window motor with integrated controller. It would report CAN bus errors and one line of the CAN bus shorted to +. Once I disconnected the CAN bus lines one by one at the junction I was able to determine that the CAN bus fault was being caused by that door motor. So I went to the JY and got a left rear window motor. Well when I opened up the door on the JY car the regulator had failed (no surprise) and the cable was all balled up around the spindle. Got the motor out, got home, and installed it on my car. Tried running the window up and down with the new motor but it would only go up and not down. So I got the computer connected and turns out the controller had sensed the jam and inhibited the motor from running down anymore. Once I cleared that code the motor ran both ways.

Long story short is that it’s pretty much impossible to troubleshoot one of these cars without a computer. But once you have the computer it will lead you right to the problem.

I only have an Icarsoft MB II. It seems it is time for me to get an SDS computer.

tyl604 · #6 09-20-2018, 07:52 PM

Jay Bob - what computer/program do you use; what do you recommend?

jay_bob · #7 09-20-2018, 07:57 PM

Bootleg Xentry system bought off eBay

97 SL320 · #8 09-20-2018, 08:07 PM

Quote:

Originally Posted by ROLLGUY

What do you mean by "brick the system"?

This is an electronics term where a bug / attempting improper operation of a previously properly operating turns the object into a brick, that you throw in a lake.

Quote:

Originally Posted by ROLLGUY

Yes, in fact the car was moved around the yard with the passenger seat out . . . The two seat controllers were not compatible ('03 seat in an '05),

The incomparable issue could have damaged the controller if wiring is different between the two. At minimum there will be trouble codes that may have put the system into a safe locked mode. ( out of operation )

First step is to use a scan tool to check for codes then clear any it has. If the system does not respond, you will need a wiring diagram / factory diagnostic tree to figure out where the problem is.

ROLLGUY · #9 09-20-2018, 08:25 PM

Quote:

Originally Posted by 97 SL320

This is an electronics term where a bug / attempting improper operation of a previously properly operating turns the object into a brick, that you throw in a lake.

The incomparable issue could have damaged the controller if wiring is different between the two. At minimum there will be trouble codes that may have put the system into a safe locked mode. ( out of operation )

First step is to use a scan tool to check for codes then clear any it has. If the system does not respond, you will need a wiring diagram / factory diagnostic tree to figure out where the problem is.

I did check for DTC's in all the related systems with my MB II, and none were present.

Paulwho · #10 09-20-2018, 09:49 PM

Rollguy,

The door control module is powered by the rear sam. Check all your fuses ,I don't remember the number. Left rear trunk side panel. Check with Key on engine off. Good luck,

ROLLGUY · #11 09-23-2018, 11:17 AM

I got the driver seat back from the upholstery shop yesterday. I installed it, and the seat and steeririg column controls work. However, the steering wheel will only go in or out now, not up or down. I am sure the up-down function worked when I picked up the car because the wheel was higher than it is now. The passenger seat has another problem too. I was able to get the rear bolts in the other day, but was not able to move the seat back to get the front bolts in. I had an extra seat control module, so I took off the rear bolts so I could tip the seat back to replace the module. I replaced it and tried to move the seat before bolting it down. It worked in all directions, so I put the front bolts in first. I got all four bolts in, and then tried to move the seat back. It would not move in any direction- not up, down, back, or forward. I was able to move it back by pressing the #3 memory button about a thousand times, moving the seat back a sixteenth of an inch each time the button was pressed. The only problem now, is that the seat back is tilted forward, and very uncomfortable to sit in. It would also not be good to be sitting there in a front collision. I am not sure what to do now. Yes I know an SDS would help me with this. I just need to find one for sale that I can afford. If I need to get the seat out again, it will be nearly impossible to get all four bolts out. I can't access the motors directly, otherwise I would hotwire them to get the seat in a good position. I do have a live data feature in my MB II, but not sure if it will reveal any useful information. Next chance I get, I may give it a try.

Father Of Giants · #12 09-23-2018, 03:20 PM

I'll chime in. Correct me if I'm wrong.

I would check for power and control on the seat and steering wheel wires right at the connector.

With the circuit at fualt loaded (on) (let's just assume it's a power side switched design, and a two wire connector), connect test light to ground.

If the test light doesn't light, you may have an open.

Connect the test light to power.

If you touch the feed or control wire and the test light is lit, you have a short to ground on the wire or a TINY chance of a shorted driver.

If it's a three wire connector, the extra wire is a signal return (ground), if you have high voltage on the signal return your ground is bad or open.

Also another thing you could do is a bypass test, assuming your feed is good, if you connect the test to the control wires the seat or steering wheel should move.

I'm at work and I have to go now, I'll add more later.

ROLLGUY · #13 09-23-2018, 04:14 PM

Quote:

Originally Posted by Father Of Giants

I'll chime in. Correct me if I'm wrong.

I would check for power and control on the seat and steering wheel wires right at the connector.

With the circuit at fualt loaded (on) (let's just assume it's a power side switched design, and a two wire connector), connect test light to ground.

If the test light doesn't light, you may have an open.

Connect the test light to power.

If you touch the feed or control wire and the test light is lit, you have a short to ground on the wire or a TINY chance of a shorted driver.

If it's a three wire connector, the extra wire is a signal return (ground), if you have high voltage on the signal return your ground is bad or open.

Also another thing you could do is a bypass test, assuming your feed is good, if you connect the test to the control wires the seat or steering wheel should move.

I'm at work and I have to go now, I'll add more later.

I would be afraid to do anything more than apply 12v directly to the motors. Jay-bob explained it well in post #2, so I am not about to mess with anything that I am not absolutely confident about. Since I was able to move the seat back as explained in my previous post, I can only assume the seat control module has power.

97 SL320 · #14 09-23-2018, 04:15 PM

Quote:

Originally Posted by ROLLGUY

I did check for DTC's in all the related systems with my MB II, and none were present.

Will the MB II get you into the body computer / seat system? The OBD2 standard does not dictate standards for seats / body.

ROLLGUY · #15 09-23-2018, 04:20 PM

Quote:

Originally Posted by 97 SL320

Will the MB II get you into the body computer / seat system? The OBD2 standard does not dictate standards for seats / body.

I think it does, but only from the live data feature. It will tell me what component is activated live. Again, I am not sure how helpful that will be. When I get some time to devote to it, I will see what comes up. For now, the car is derivable (and with nice new upholstery on the seats!).