C4 Picasso Mk2 – Intermittent C003A Rear Right ABS Fault – Sensor Replaced, Still Returns

[CallyyllaC]

Hi all,
Looking for some advice before I go further down the wiring/bearing route.

Car:
C4 Picasso Mk2
1.6 DV6, 6-speed manual
94k miles

Fault codes (RAC diagnostic):

Code: Select all

Name:ABS - BOSCH ESP90
DTC:C1391,Engine torque non acknowledgment
DTC:C003A,Rear right wheel speed sensor

Name:POWER STEERING - SMI/JTEKT
DTC:U1213,Fault in communication between the electric power steering ECU and the ABS/ESP ECU

warning lights come on when accessing ABS module
live data - wheel speeds currently working ok
cleared fault memory
could not fault vehicle on attendance
checked plug - ok, no corrosion or water ingress
wiggled wiring - fault codes did not return
suspect wheel speed sensor intermittently defective

Description:
Driving to the office last wednesday, fine for 72 miles mixed town/ a-road/ dual carriageway, just finished driving through the village to the industrial estate, last corner to work my dashboard lit up like a Christmas tree.

These are the errors from the car's diagnostics menu.
RAC came out to inspect, performing a wiggle test on the wire, checking the connectors, and determining that the issue was likely due to the sensor being intermittent.
They cleared the codes, and I got about 30-40 miles down the dual carriageway before the lights came back on.
Replaced the ABS sensor. At first it didn't work, and the lights all came back 2 yards down the road, but I think that was because the o-ring was twisted and it wasnt sittting flush.
After replacing it again, I gave it a bit of a drive; the errors cleared up after 4 minutes or so (I was told it needed to calibrate internally?), and my abs came back to life.
2 days later, after a full day of town driving and 73 miles to work and 72 miles back (normal driving, assuming it was fixed), I got about halfway through my hometown before it decided to fail again.

Current suspicion is an intermittent wiring issue between the sensor and esp arch section. I've seen multiple posts on this forum also indicating that this is the case, but I'm not a mechanic and wanted a second opinion before I started taking the wheel off (again...) and started cutting.

I don't think it's:

• Sensor – already been replaced, and the symptoms didn't change.
• Ring – I assume that would cause a more consistent fault?.
• Connector at wheel – it looked clean, sprayed it with contact cleaner, still looks clean.
• Battery – There were some power-related codes in the RAC report, but nothing major. I do have an issue with my alternator pulleys wearing though, which could cause those.

[*]Tyres/tracking – tracking is slightly out and booked for alignment, but unsure how that would cause intermittent single-wheel dropout.

Questions:
Has anyone experienced similar intermittent rear ABS dropout on these?
If so, was it:

• Wiring in trailing arm flex section?
• Encoder ring/bearing?
• Connector corrosion further upstream?
• Voltage related?
• Something I haven’t considered?

Thanks in advance.

[PaulC5]

There have been many posts on here with similar faults and it has been the wiring to the back that has broken/corroded. It needs to be checked all the way, not just at the end.

[RichardW]

Welcome along.

It's most likely to be a rot spot on the wire - very common problem as the wire is unprotected in the conduit. Had to do ours a while back, note that the area of damage may be very small!

https://www.frenchcarforum.co.uk/forum/ ... &start=622

[mickthemaverick]

If you watch this video, a bit long winded, from around 9 minutes he shows what and where the fault was, The first part shows him changing the speed sensor with no effect but the second part solves the problems which appear to be very similar to yours. Good luck

[CallyyllaC]

Thanks all, I'll have a quick look tonight after work and see if there is anything obvious, if not, then it will be a weekend deep dive.

[CallyyllaC]

Okay, well that took all of 30 seconds.

Saw a mounting point that was more rusted than the others and still damp despite no rain today. Pull out that section of cable... see a blue spot.

Unless there is somehow more dead spots I can't see I think this is it, the rest of the cable looks shockingly good. (That was not a pun based on the current state of that shock absorber)

[mickthemaverick]

Excellent, pretty much exactly the same as the guy in the video.. Well done and lets hope all is well when you've fixed it!!

[RichardW]

Yep, that's likely to be it. Green Crusties 'r us!

[BarneyRubble]

Perfect, really glad you solved the problem, and thanks too for posting your results!