Citroen C4 1.6 ABS Wheel speed sensor fault.

This is the Forum for all your Citroen Technical Questions, Problems or Advice.

Moderator: RichardW

citc4
Posts: 6
Joined: 03 Jan 2022, 18:36

Citroen C4 1.6 ABS Wheel speed sensor fault.

Post by citc4 »

Hello,
I have some struggle with an LH front ABS wheel speed sensor, the old sensor has been replaced plus we have replaced the ABS module (w/brakelines)
The scanner says that there is short or a no ground to the sensor.
My question is how does the ABS wheel speed sensor circiutry look like.
We have tried to clean all the plugs going into the BCM and the ECU with no luck aswell, but do somebody knows where i can find the pins for the front left ABS wheel sensor.

Best regards and happy new year 😉
Last edited by citc4 on 04 Jan 2022, 15:45, edited 1 time in total.
wheeler
Posts: 5376
Joined: 21 Sep 2002, 19:07
x 340

Re: Citroen C4 1.6 ABS Wheel speed sensor fault.

Post by wheeler »

Need your VIN to get a wiring diagram.
Does the fault warning appear as soon as the car is started or only once you start driving?
citc4
Posts: 6
Joined: 03 Jan 2022, 18:36

Re: Citroen C4 1.6 ABS Wheel speed sensor fault.

Post by citc4 »

Thank you for the reply.

The fault is coming 5 sec. after startup.

The VIN is V57LCNFUC74283323
Online
User avatar
GiveMeABreak
Forum Admin Team
Posts: 26538
Joined: 15 Sep 2015, 19:38
x 3104

Re: Citroen C4 1.6 ABS Wheel speed sensor fault.

Post by GiveMeABreak »

Here you go.

Most codes are on the wiki here in sections based on ascending order:

https://frenchcarforum.co.uk/wiki/Elect ... ring_Codes

Image
citc4
Posts: 6
Joined: 03 Jan 2022, 18:36

Re: Citroen C4 1.6 ABS Wheel speed sensor fault.

Post by citc4 »

Thank you for the schemematic.

What i have tested out so far

7810 - 1-26 = 0.0 ohm
7810 - 2-5 = 0.0 ohm
7810 - 1-2 = IO

7800 - 4-GND 0.0 ohm
7800 - 1-GND 0.0 ohm

Still no signal to LH front wheel speed sensor.

Any ideas?

Best regards.
wheeler
Posts: 5376
Joined: 21 Sep 2002, 19:07
x 340

Re: Citroen C4 1.6 ABS Wheel speed sensor fault.

Post by wheeler »

Have you checked that wires 7001U & 7002U are not shorted to earth?
Has anyone replace the wheel bearing on that side? Have you tried (carefully) cleaning the magnetic track on the wheel bearing? over time metallic dust can build up on them & cause bizarre/incorrect readings.
citc4
Posts: 6
Joined: 03 Jan 2022, 18:36

Re: Citroen C4 1.6 ABS Wheel speed sensor fault.

Post by citc4 »

Thank you. I cant remember but I think that there is continuity between either 7001U or 7002U to earth. but where could this happen possible?
The wheel bearing has been replaced because it was worn out.
Its still the same error with the new wheel bearing.
Thanks again.

Best regards.
wheeler
Posts: 5376
Joined: 21 Sep 2002, 19:07
x 340

Re: Citroen C4 1.6 ABS Wheel speed sensor fault.

Post by wheeler »

citc4 wrote:
04 Jan 2022, 16:29
Thank you. I cant remember but I think that there is continuity between either 7001U or 7002U to earth. but where could this happen possible?
It could be anywhere really. Did you check for short to earth with both the sensor & the ABS ecu unplugged? Another option would be to run new cables directly to the sensor from the ECU.
citc4 wrote:
04 Jan 2022, 16:29
The wheel bearing has been replaced because it was worn out.
Its still the same error with the new wheel bearing.
Thanks again.
Are you saying the fault existed before the bearing was replaced? Was the new bearing installed the correct way around with the magnetic track towards the sensor?
citc4
Posts: 6
Joined: 03 Jan 2022, 18:36

Re: Citroen C4 1.6 ABS Wheel speed sensor fault.

Post by citc4 »

Hi,

I disconnected both the ESP ECU, and the wheel speed sensor, and then measured GND on both terminals. Tomorow i will try to run new cables, if they are, or one of the terminals are shorted to earth. I thought that it should be like + - on the sensor i remember.

the bearing is with its magnetic side facing the wheel speed sensor, and the fault existed before the replacement.

One thing i found, was that two wires on the BCM were soldered together WHITE TO GREY on the third plug on the BCM module.

I think i would try to see if the white wire connects to pin 5 or 26 on the ESP ECU unsoldered.

Best regards.
citc4
Posts: 6
Joined: 03 Jan 2022, 18:36

Re: Citroen C4 1.6 ABS Wheel speed sensor fault.

Post by citc4 »

Today i found out that the sensor is not shorted to ground when the plug is not connected to the ESP module. The reading in ohms match the reading on the right front wheel. BUT the left wheel sensor is getting 14V when the engine is running. the other one that is working fine. is getting around 0.2 with the engine running. Could it be a relay that is failing.

Side note:
all the sensors except the left front wheel speed sensor is measuring KPH.

Best regards.