ABS warning light - Permanent Fault Wheel Sensor Signal fix

ABS warning light appears on the dashboard. First time it came with a warning gong, subsequent times there was no sound. The light can be reset with by switching the ignition off. With the ignition on, the warning light appears without moving a wheel and after about 5 to 10 seconds.


Lexia code says:

Permanent fault
Front LH wheel speed sensor signal Open circuit, short circuit to positive, short circuit to earth



A suggestion for this fault is to remove the offending sensor and clean the magnetic track. It is also worth cleaning the sensor. There was more dirt on the sensor than the track for this C3.


To remove the sensor and clean the magnetic track, remove the 13mm rusted bolt, and keep the broken washer (it is still has one). Lever up, carefully, without breaking the plastic, the whole sensor from its housing. You can see it partially lifted in the picture. Getting started is the hardest part.



With the sensor removed, it can be cleaned with a cloth. A small brush or rolled up cloth and be poked into the hole. With the brush or cloth in place, rotate the brake disc to simulate wheel rotation and clean the magnetic track.

Refitting the sensor is much easier than removal, but it is still tight in its housing, tap it back into place.


While I was there, I loosened the inner arch near the side repeater to access the ABS Sensor plug to meter it. 1666 ohms seems ok, and put it back together.


The fault didn't come back with the ignition, stayed off for a run and more importantly, stayed off for the MOT tester

Thinking back, which may or not be relevant. The ABS fault light came on very soon after, say, within 200m of a very heavy braking episode that gave the amazon driver a fright. No contact was made, no exchange of details, just a friendly wave.

Live data showed the 4 wheels matching the vehicle speed which made me reluctant to blame the wheel sensor but the clean did the trick.

Great guide, did this in 1/2 hour, two tips, first of all bolt cant be taken out with a normal spanner as it's sunk, I used a dog bone spanner or of course you can use a socket, second tip the sensor was as stated fixed in tight so I put a screwdriver in where the bolt was and twisted it loose, it is plastic so be careful but there isn't a thread in it the sensor it's in the main body so you won't damage the thread,

Great guide, I did think that I should have a new sensor on standby but the amount of spare parts I have in my house that I've bought "just in case" and never used is beyond a joke.

Neilcmusic1 wrote: ↑Wed Feb 16, 2022 5:17 pm the amount of spare parts I have in my house that I've bought "just in case" and never used is beyond a joke.

As a professional and amateur technician, I can tell you: "If you have a spare...that part will never break". Better than auto insurance!