C4 Picasso - wheel related faults on dash

[GiveMeABreak]

Hard to say whether this is hardware related (your VCI) or software related. We know that older hardware revisions of the VCI may not communicate with the Vehicle. But if you are sure you have a full chip CAN interface then the issue may well be down to the ECU itself if this is what is giving the original problems. It would explain the lack of communication with the ECU if there is an intermittent connection / communication issue with the ABS / ESP ECU itself. If there is a wiring short, exacerbated by water when raining, then there could well be an exposed wire somewhere that has worn through the shielding.

[danlat1415]

I'm sure I have the full chip VCI (revision C - with the round pin connector between the VCI unit and the ODB port connector).
I used to have revision B which didn't have the round pin connection section, straight from VCI to ODB.

I've requested to borrow a friend's over the weekend that's definitely a full chip.

I've not used Diagbox 9 prior to this, as v7 worked on my previous C4 Picasso.

It's been raining since my last test, so I've not been able to run it when the issue has gone - but I've run it again and during the initial compatibility test, it ticks ABS as compatible, when after a global test it says ECU not recognised and when I go into it, it says ECU not recognised - communication error, but also a short to ground.
It doesn't give me any side (was hoping it would say something like - rear right short to ground).

I'll just have to get stuck in and find the shorted wire by hand.

[GiveMeABreak]

That's my point really Dan . If there is a comms issue with the ESP / ABS ECU itself especially with the CAN wiring, then of course you won't be able to get any specific data, as the ECU won't be able to communicate to tell you what the specific issue is. It will just give the generic communication fault when interrogated - as in the VCI can't talk to the ECU itself.

[danlat1415]

I finally managed to re-run Diagbox when the issue wasn't present as it's been nice weather today.
I've got a 10 month old, so spare time is rare.

It's now confirmed the issue as shorting to ground on the rear right wheel speed sensor - so you were exactly right

I've added a screenshot, just because it shows the wheel speed readings (this was whilst stationary with parking brake on - so I assume it was the last speed when issue was present.

They're all around 26-28, but the rear right is about 6.
Would it still show results like this if it was just a worn wire, or would the low speed reading indicate that it may be the actual speed sensor may need replacing?

[GiveMeABreak]

A wheel speed sensor issue alone won't stop communication with the ESP ECU Dan. There must be something else going on regarding no comms with the ECU when it's wet / raining, so that's of concern to me. But whilst it is working you have the rear right sensor reporting a speed fault.

Whether it's a wire in this case that's providing inconsistent data or the sensor itself I can't say from here of course.

[danlat1415]

To update this thread;

I have replaced the rear right speed sensor and also checked the wiring on that side. I couldn't find and wear marks or green spots on the wiring, but I did notice that the plastic tube covering the wiring loom, has the split separating section underneath near the rear wheel, but as it goes over the rear axle and towards the front of the car, the split opening section had twisted up to the top.
So I figured if any water was getting in there and shorting out the wire at any small split, then the water is getting trapped - so I twisted the cable cover so that the opening was at the bottom, so water wouldn't get in from above, and could escape from below.

This seems to have fixed my issue fully for now.
I don't get any errors at all, I can read the ECU in Diagbox and don't get any errors after clearing the fault.
The speed sensor is also reading correct now instead of just 6km/h when the others with 25+.


I decided to replace the speed sensor because the speed readings were incorrect on that wheel. The others seems to be slightly out, but it was last ready whilst I was reversing parking whilst turning, so the front wheels had slightly different speeds, as did the rear left wheel - with the rear right completely wrong.
I don't know if the water ingress was on the sensor itself or on the wiring loom, but replacing the sensor and adjusting the wiring loom trunking cover had resolved my issue (at least for now)

Thanks for your help and advice everyone.

[GiveMeABreak]

Great, thanks for updating Dan.

[danlat1415]

Another update to this. The fault returned after a few weeks of silence.

I then checked the wiring loom going from the driver side rear wheel speed sensor along the rear axle.
I found that the small twisted 2 wires, one of them had a green spot on it where it had worn though and the copper wire had oxidised.
I cut the oxidised section out and used the self soldering wire connectors to connect back up (the ones you heat up with a heat gun or cigarette lighter).

The awkward thing was that the split wire section was right up by the rear axle towards the front of the car where the wiring loom starts to disappears into the underside of the car, so space was very restricted.

All permanently sorted now (fingers crossed).