2009 C4 Grand Picasso ABS issues

[HardNock]

Hey all, I'm new here but have owned Citroen and / or Peugeot cars most of my driving life. I purchased a 2009 C4 Grand Picasso VTR+ 1.6 HDI with a 6 speed semi-automatic gearbox (VIN VF7**************[VIN obfuscated, can be read by forum staff]) in March of this year. Lovely car, very clean for the year. I had no issues with the car until I had a tyre replaced and tracking altered, after which I was getting intermittent issues with an ABS sensor (triggering the usual ABS / EPS / Parking Brake / Gearbox fault messages). DiagBox (and an Autel diagnostic handheld device) both displayed error codes C1 331 Front right wheel speed sensor signal fault and unable to select higher than third gear. Stopping the car, turning off the ignition and starting the car back up then pull off and drive cleared the fault, assuming because the speed sensor was picked back up. This was quite intermittent and only seemed to really occur on longer drives when getting to 50+ MPH. The speed / ABS sensor itself was disgustingly filthy so I cleaned it up but the issue remained. I purchased a new sensor and fitted it, but now the fault is permanent. If I clear the fault and drive off, the same fault re-occurs almost immediately. I removed the new sensor thinking it may be faulty and re-fitted the old sensor, but this also now triggers a permanent fault. I've removed the wheel and cleaned around the whole hub, wheel bearing and driveshaft as they were pretty dirty but the permanent fault remains. I can't drive the car any more as I can't select higher than third gear. When I check live data, there's voltage on each corner so the sensors are being detected by the module. Any ideas? I'm now at a loss! I don't want to believe the ABS unit itself is faulty, it seems too coincidental that the fault only occurred after a tyre change and tracking adjustment (the tyre was o/s rear, so not the same corner as the fault) and the permanent fault only occurred after changing the sensor.

[HardNock]

So I've checked the 5A fuse and wiring feeding the ABS unit and can't see any corrosion. I've bought a new Active Sensor Bearing (wheel bearing) for the same corner and fitted that, still have the same issue. So frustrating because the car is stuck at my brother in laws garage 30 miles away and I can't even drive it home!

[HardNock]

I fixed the issue and thought I'd post the solution in case this crops up with someone else. The sensor and active sensor bearing both turned out to be fine and functional, as were the connectors and electric harness. It turned out that the sensor mounting had been knocked slightly out of place somehow. The only work done to that corner was the tracking correction, as mentioned in my original post. I took measurements and compared them with the n/s front corner and the o/s front corner which returns the error differed by a few mm. I manipulated it back into position and the error hasn't returned since.

[Craigycraigo87]

Hey, just wondering if stayed fixed or not, and what exactly you mean by knocked out of place as when I looked at mine today it kinda just sits in one way . pulling my hair out ATM haha.hoping to try new sensors on monday.cheers
Craig

[dasachtach]

Hi. I had the very same issue. Fixed recently. I pulling my hair out for over a year with this. Started with the usuall, ABS, automatic gearbox, auto park brake warnings etc. Went to the trouble of getting Diagnox and found "no signal left front wheel speed sensor"
Replaced sensor and still the same. Ended up replacing all the sensors, cleaned the magnetic part on each hub, still the same messages.. Read on theese forums that wiring may be an issue. Stripped the whole wiring harness inside the firewall. All looked good. Cut each wire at the sensor and rewired back to the abs unit. Still the same! Drove for a year like this, changing gears from 1st to 3rd with the paddles, then selecting Neutral and back to Auto to get the gear box to select a higher gear... just got used to it in the end. Not ideal though driving around without ABS. The car was coming up for it's NCT ( yearly inspection) and I knew it wouldn't go through like this, so I resigned myself to the fact it was to be scrapped.. seemed such a waste but I'd done all I could. Or so it seemed. Went out the day before I was to bring the car away to the breakers yard and thought I'd have one more look. Got to thinking, where did the issue begin? Well it all started with the front left wheel speed sensor.. So I had a look, all looked like it was in the correct position.. But I took it out anyway.. a tiny bit of rust just where the lower part of the sensor sits.. I mean not even half a millimetre....I used a wire brush and a file to clean it , put back together and.. no warnings whatsoever!car drives perfectly and passed it's inspection today.. hope this helps somone...
.As I say I was just hours away from bringing it to the breakers yard, and all for a sensor out by half a millimetre....