Citroen C4 – STOP, service, unstoppable wipers and other electrical problems.

[samks]

Hi.

My Citroen C4 1.6 HDI 2007 aut. recently started having a total electrical meltdown. Mechanically the car runs well – it’s all electrical. When I start the car, following faults appear:
- ABS faulty
- Speed control faulty
- Service light
- STOP light
- A-bags/s-belts faulty
- Braking system faulty
- ESP faulty
- Wipers and light turn on themselves.
The wipers and light continue when I turn off the car and the only way to turn them off again is cutting the power from the battery – or being lucky as they randomly turn off after some time. The wipers and light are not constantly on and blinks/stutters at times.

I tried the following:
- Measured resistance between CAN_L and CAN_H – 63 ohms
- Removed all EGR-related plugs
- Removed the radio
- Replaced BSM
- Replaced ECU
- Replaced BSI
- Checked all fuses in engine bay and under the steering wheel
- Replace battery
- Cleaned all earths I could find in the engine bay
- Cleaned a lot of plugs in the engine bay
The problem persists even with the ECU removed.
I have access to Diagbox so I checked if the control unit for the wipers sends a request to wipe which they don’t. Instead, they change from “no request” to “failure”. I thought the BSI was malfunctioning, but the problem persists after replacing it. Are there any obvious wires to check?

What can I try at this point?

Thanks

[wheeler]

The first thing that jumps out at me linking all these faults is the comms unit behind the steering wheel (wiper & lighting stalks).
The only thing i cant remember is if the steering angle sensor for the ESP is in this unit on cars with fixed centre steering wheels.

[GiveMeABreak]

Those were my thoughts too and yes the Steering Wheel Angle sensor is still in the same place.

[wheeler]

Had to check this as there was something at the back of my mind telling me the steering angle sensor is separate to the coms unit, on the fixed centre steering wheels the coms unit is horseshoe shaped & can be removed with the steering wheel still in place. Still leaning towards coms unit but not sure now how the ESP/ABS faults are linked.

[Hell Razor5543]

I would guess that, if the steering angle sensor is playing up, the ESP would not 'know' where the steering was pointed, and so it (and, because they are linked, the ABS) would have a hissy fit.

[wheeler]

I understand that & if it was a model without a fixed centre steering wheel then the steering angle sensor is incorporated into the com2000 unit which also links the Airbag, wiper & lighting faults, on this C4 The angle sensor is a separate part from the lighting & wiper stalks though. If it was a model with the angle sensor i would have said coms unit all day long.
I am still leaning towards comms unit though.

[samks]

Thanks for the replies.

My 2007 does have a fixed steering wheel. I tried unplugging the com2000 unit as well as steering wheel angle sensor (I think) which made the wipers and light less erratic, but I still have constant STOP, blinking service, ESP, gearbox faulty etc. So I'm not sure the com2000 unit is to blame?

Since first posting I have tried to remove all fuses in the engine bay, but to no avail. I also tried removing most fuses under the dash with no success.

Using a bluetooth OBD I read following faults: u0415 p0490 p0401 p2127 (and more, see https://photos.google.com/photo/AF1QipM ... MJfel0QGnY)

[wheeler]

Well if you unplug the angle sensor the ESP/ABS light will definitely come on.
When the com2000 cant talk to the BSI it goes into backup mode which makes the lights & wipers come on.

[samks]

Exactly what I thought too!

I just tried a couple of things and the problem definitely seems to be connected to the steering somehow as I can make the wipers turn on by turning slightly. It's not the steering angle sensor as the problem persist with it unplugged.

But I still have a hard time believing it's the COM2000 because the STOP light (braking system faulty) remains with the COM2000 unplugged?

This is what Diagbox looks like with the motor running and wipers/light going crazy: https://photos.app.goo.gl/r8NbRs6HLdyq6pFt8

[samks]

Any suggestions before I buy a new COM2000? I really doubt it will fix anything.

[samks]

Now I have made some measurements and it turns out, as expected, that the CAN bus is short-circuited.

Between CAN_L and CAN_H I measure 0 ohms when the car is off and started. With ignition there is + 0.3V between CAN_L and CAN_H, +2.6V between GND and CAN_H and + 2.3V between GND and CAN_L.
If I take the 3rd smallest plug out of the ECU, I measure 125 ohms without ignition. When I turn on the ignition, I measure 0 ohms again.

I've tried to take the COM2000 out and it made no difference, so it's probably a misnomer. The short circuit also does not disappear by taking the two plugs out to the gearbox, the ones at EGR, or the additive pump

[samks]

I ended buying a new COM2000 unit and it didn't fix a thing