Hello everyone,

My 2005 Grande Punto has an ABS fault which is giving code C0031 for left front wheel speed sensor (there is also intermitted code C1215 for the brake light switch but that it intermittent). I took the sensor out and it seems to be fine, no damaged wires but obviously it's difficult to tell.

Before I order a replacement sensor to does anyone have any suggestions for what else might cause this fault? I read elsewhere that a poorly replaced wheel bearing could cause this, so I'll see if I can compare left to right without dismantling everything.


I checked the ABS control unit plug and it all seems clean. I waterproofed the contacts whilst I was at as recommended in the guides section, but it didn't remove the fault code.

Is there anything else anyone can suggest checking? Any tests I could do? I suppose I could test continuity in the sensor, anything else?


Also, whilst I was there, I found another wire attached to the strut which didn't seem to connect to anything. Is this some other sensor? It is in a cable wrap and goes back into the main loom but after that I don't know where it goes.

Thanks

There are only two cables in the strud area: one for the ABS sensor and the other is for the brake pad wear sensor.
Regarding the ABS sensor, you'll probably not be able to check it since it's a "Hall effect" sensor and you'd have to hook an "O'scope" on it to visualize its output. Thru the hole left by the sensor, you can see the "phonic wheel" on the CV joint if it's the old system. This needs to be free of dust/mud in order to work properly, give it a compressed air blast. If it's the new style (you can't see any tooth), then the magnetic track is on the bearing.
Here is the drawing so you can check the signal(s) directly at the ABS plug.

BRs, Bernie

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Thanks for the info Bernievarian.

I'll take the right and left sides apart at the weekend and see if I can see a difference in the bearing. The left (faulty) side doesn't have a toothed wheel, so I've no idea if there's a magnetic track on the bearing. I could probably connect a multimeter to the wires at the plug in the wheel arch, this might indicate something as the axle turns (I have one which can measure duty cycles so it might also be able to display the output of the hall effect sensor, I'll check the instructions).
That drawing will be useful too, I can check continuity of the wires from the ABS unit to the wheel arch. But there seem to be three pins for the left front, 2x left front sensor positive and 1x left front sensor signal... I think one of the left front sensor positives must be the right front sensor positive. Or am I reading it wrong?
The wire attached to nothing that I have attached to the strut must be for the brake pad wear sensor. Maybe that's not implemented on my car, or maybe it was cut off for some reason, but wouldn't that give an error?
I'll check all this at the weekend.
Thanks again

If you can't see tooth in the sensor's hole than you most probably have the magnetic track built on the bearing AND the Hall-effect sensors, which seems to be confirmed by the 3 wires...

The "extra" loose wire is the pad wear one and should only lite a light if connected to ground, which happens when the pas is worn and the cable goes in contact with the disk.

Unfortunately, schematics in FIAT's e-Learn are not always up-to-date, but here's one I found with a (generic) Hall-effect ABS sensor.

BRs, Bernie

If someone here helped You fix -or better, understand- your issue, hit the thanks icon @ bottom right corner, it's free and makes us feel helpy ;-)

Ive had similar faults on 2 cars.
One being an Alfa and the other a Suzuki.

On the Alfa, the speed sensor was at fault.
There were no visible indications as to it being faulty.
Only after biting the bullet and changing it, did the fault go away.

On the Suzuki, the ABS ring was cracked

First chance I've had to get back on the forum!

I swapped the sensors from one side to the other, started the car and checked the OBD output and it confirmed that the fault had moved sides, so it confirms the wheel speed sensor is the problem, which is great as that's an easy repair!

Top tip for anyone else who has this fault - swap the sensors to see if the problem swaps sides

Thanks for the update, job well done (and good troubleshooting practice !)

Cheers, Bernie