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½cwt

ABS Light

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Got my car in with local OPC today for a new key and a fault code sweep as I have ASB light on. I've cleared the code twice with the full lock to lock reset, but it keeps coming back. OPC report no stored fault code.  Where to next?

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Light has now starting to be off on start up and then coming on after a few minutes...

Any ideas anyone?

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When you say off ,does it not come on and go out after a few seconds on start up.

Does your car have traction control (not psm).

I presume they checked for pending and stored codes when they scanned it.

Sounds like a signal issue, i.e. sensor, sensor wiring or corroded pulse ring on a hub giving a spurious signal although these should give a fault code.

You say comes on after a few minutes, is that few enough to run the car stationary for the time period to see if the fault comes up without driving (rotating wheels).

If it does not come on depress the brake pedal and see if the fault comes up.

If it still does not come on drive it and if it comes on it's likely to be signal related.

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44 minutes ago, Shazbot said:

When you say off ,does it not come on and go out after a few seconds on start up.

Does your car have traction control (not psm).

I presume they checked for pending and stored codes when they scanned it.

Sounds like a signal issue, i.e. sensor, sensor wiring or corroded pulse ring on a hub giving a spurious signal although these should give a fault code.

You say comes on after a few minutes, is that few enough to run the car stationary for the time period to see if the fault comes up without driving (rotating wheels).

If it does not come on depress the brake pedal and see if the fault comes up.

If it still does not come on drive it and if it comes on it's likely to be signal related.

Yes, it comes up on the start up sequence and then goes out, only to come on after a short period, other times it stays on.

I haven't noted whether it comes on after first braking or at another time yet.

No codes flagged for ABS (or anything else).  I was expecting a hub sensor fault code or ABS pump as these are the most common but nada...

I'll try the test sequence you say above.

 

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Could be the brake pedal switch, as mine was coming on randomly, finally worked it out was caused by the brake pedal switch.

But only when you pressed the brake pedal switch very gently.  Could get light to come on with it just idling on the drive.

Turned out there was state on the switch where it wasn’t in any condition. I.e. pressed or not.

causing the ABS module getting confused 

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5 hours ago, Sanky said:

Could be the brake pedal switch, as mine was coming on randomly, finally worked it out was caused by the brake pedal switch.

But only when you pressed the brake pedal switch very gently.  Could get light to come on with it just idling on the drive.

Turned out there was state on the switch where it wasn’t in any condition. I.e. pressed or not.

causing the ABS module getting confused 

Quantum brake switch, interesting...🤔  I'll include that in my checks.

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OK, so I invested in a fault code reader that will talk to more than just the basic OBD2 bits of a 986, and whilst the OPC said there was no fault code, this unit has shown front left ABS sensor 🤔.  One new Bosch sensor on order to match 996 640 406 00.  Hope this clears it!

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If the car isn't a daily what about swapping the front sensors over to see if the fault moves. 

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1 hour ago, ½cwt said:

OK, so I invested in a fault code reader that will talk to more than just the basic OBD2 bits of a 986, and whilst the OPC said there was no fault code, this unit has shown front left ABS sensor 🤔.  One new Bosch sensor on order to match 996 640 406 00.  Hope this clears it!

So much for the OPC who looked at it.

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1 hour ago, Sanky said:

So much for the OPC who looked at it.

At least they had the decency not to charge for not reading it... 

From research I had suspected it might be the front left sensor as that seems to be a common failure on RHD cars.  First to hit all the cr*p on the side of the road.

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