C4 Picasso (2008) - Error Between Wheel Sensor and ABS ECU

[layls]

Hi,

My Citroen C4 Picasso (2008, VIN: VF7**************[VIN obfuscated, can be read by forum staff]) is showing an array of errors:

- Handbrake faulty
- Braking system faulty
- Airbag(s) or pretensioner seat belt(s) faulty
- Depollution system faulty
- ABS braking system faulty
- ESP / ASR system faulty

The handbrake warning is the oldest. The other errors have arisen, intermittently at first, over the past few months. They are now constant.

Additionally:
- The handbrake won't go off or on (even after the switch component on the central console has been replaced for new. It can still be applied / removed using the crank in the passenger footwell)
- There is no hill start
- The speedo doesn't work

Despite all of this, the car does actually drive fine.

In the past 2 years the car has (in chronological order):
- Passed all of its MOTs but we were warned 2 years ago that the handbrake motor has limited travel and may at some point need replacing
- Had a run-in with a pothole which bent the shock on the front driver's side. This was repaired.
- Had a new caliper on the front driver's side.
- Had a slow leak on the front passenger side tyre. The engineer took the tyre off, stripped the old flaky paint from the inside of the rim and resat it <= after this point, the multiple system errors began
- Had new discs on both front tyres.
- Been seen by our local garage. Their diagnostics indicated an error with the front passenger side wheel sensor. This was replaced for new. <= after this point, the errors persisted
- Been seen by an auto electrician. Their diagnostics still showed an error with the front passenger side wheel sensor. They took the newly installed wheel sensor out, cleaned it up, and resat it. Then reset the system. <= The errors went away for about 24 hours, then reappeared.
- Been seen by a Citroen specialist garage. They have investigated and are confident that there is an electrical issue between the wheel sensor and the ABS ECU. However they do not have the time and resources to find and diagnose it.

I'm considering investigating myself to see if I can locate the fault. I'd be very grateful for:
(a) any advice!
(b) any relevant wiring diagrams

Cheers, L

[RichardW]

Welcome along.

You need a full scan first to see what errors it is actually reporting. All the brake warning lights come on if there is an engine issue - not neccessarliy anything to do with the ABS! Then you need a decent scan tool that can read live data so you can graph the output from the sensor (assuming that is the fault...) to see if there is some sort of signal. It could be that the mag track on the bearing is faulty.

[mickthemaverick]

I'm afraid that we have currently lost our access to the Stellantis database so I cannot get the wiring diagrams for you. There are some members with their own access so if one of them sees your query they may be able to help you out. In the meantime I would carry out a methodical clean of all the plugs and sockets around the Engine fusebox and follow the wire from the wheel sensor as far as you can looking for chafing or potential breakages at connectors etc. You may come across the problem and solve it. Once you have done all that carry out a BSI reset as per the procedure linked below and then see how it is.

viewtopic.php?p=601679#p601679

[PaulC5]

Picassos are known for the wiring to the rear brakes getting damaged so you could follow it back into the car looking for minute damage although I do not know if it applies to ones as early as yours. viewtopic.php?p=847405&hilit=handbrake#p847405

If you get stuck why not try a Citroen dealer.

[layls]

Hi everyone,

Thank you for the warm welcome and excellent advice.

Re: the scan, my original next step was going to be taking the car to a Citroen dealer for a diagnostic scan (£160). But the last mechanic I saw (the Citroen specialist) said it wouldn’t reveal anything his tools hadn’t already - although he didn’t share specific fault codes with me, just the overview I included in the original post.

Do you think it’s worth going for the dealer scan after all? Or is it better to get the diagnostic kit myself? I’m keen not to spend too much on a car that may be beyond economical repair, given its age! (Although I’m fond of it, and would love to get it fixed)

[mickthemaverick]

If the dealer scan is £160 I'd say you can get a decent scanner for not very much more, possibly even less, and so if you are going to keep the car and you are reasonably confident of being able to use the kit yourself, you may be better off in the long run to get a scanner and then maintain the car ongoing!!
Something like this may be ideal but I have no direct knowledge of this unit although I am aware that many mechanics use the Launch range:
https://www.ebay.co.uk/itm/277114880284 ... R6LCl_OeZg

[shtu]

Berlingos suffer from breakages to the wiring to the rear wheel sensors.

https://www.berlingoforum.com/thread-21206.html

The other approach to prove the fault is a wiring break would be to do a hacky rewire, running cables from the sensor's plug to the relevant pins on the ABS module, and test that. (the correct full fix is of course to find the break)

[layls]

Thanks for the link!

If the dealer scan is £160 I'd say you can get a decent scanner for not very much more, possibly even less, and so if you are going to keep the car and you are reasonably confident of being able to use the kit yourself, you may be better off in the long run to get a scanner and then maintain the car ongoing!!
Something like this may be ideal but I have no direct knowledge of this unit although I am aware that many mechanics use the Launch range:
https://www.ebay.co.uk/itm/277114880284 ... R6LCl_OeZg

[layls]

That could be a really handy quick test! Thanks for the idea

Berlingos suffer from breakages to the wiring to the rear wheel sensors.

https://www.berlingoforum.com/thread-21206.html

The other approach to prove the fault is a wiring break would be to do a hacky rewire, running cables from the sensor's plug to the relevant pins on the ABS module, and test that. (the correct full fix is of course to find the break)