Possible 1st ever trip to a garage with a problem, ABS

[cyclonebri1]

In true miserly tradition, I have yet to take a car to the garage for anything other than the mots.
But I'm stumped with this 1 so I may have to admit defeat and cough,

Renault megane est, ABD and ESR and ASR warnings lit up.


If anyone can sense check this for me I'd appreciate it

All wheels removed and sensors cleaned and wiring inspected, all looks well.

Reluctor? rings not visible, part of the drive shaft at the front and the wheel bearing at the rear.

Resistance of each sensor checked, all 12 ohms, there must be a diode in there as they are polarity sensitive.

Car lifted and an ac voltage check on all sensors whilst spinning wheels, no reading on either an analogue or digital meter. Checked either polarity.

After removing half the under bonnet and bulkhead arrangement, including the wipers, I finally gained access to the ABS ecu, it's part of the ABS hydraulic unit. Removed wiring connector, cleaned, and refitted.

OBD11 doesn't interrogate this ABS ecu, needs a more specialised scanner methinks.

As I understand it the ABS ecu checks the resistance of each sensor whilst stationary, in the 1st 2 seconds, then the output of them when on the move.
The light comes on whilst stationary.

Anyway, no better, car can be driven but brakes revert to non ABS operation. MOT failure of course.

So unless anyone has any ideas or something I may have missed it's a trip to the rip off specialists.

[AlexB]

Have you read MR366MEGANE3.pdf? It can provide clues to what to check.

The ABS rings are magnetic plastic glued, as you wrote, to the corresponding metal parts.

The ABS light may stay on for a while after fixing the fault. This complicates the experiments which do not involve Clip for force resetting the light.

I have no experience with this, to be honest. Try reviewing the history, the context of the fault, then read, then check the likely causes... It seems to me that without Clip one can only keep guessing.

[cyclonebri1]

Thank you alex, I did wonder if I'd actually fixed the issue and it simply needed resetting, but to be honest I'm at the limit of my experience after a lifetime of motoring practice.

I have heard of chip, is this the official renault interrogatory system? or something non franchise outfits use?

I'm afraid I have little faith in my two renault dealers, the car went in to both for warranty work and came back worse or had to go back several times.

[AlexB]

It's "Clip", not chip... Yes, it is Renault proprietary, but there are replicas sold on ebay and everywhere else, which work. I don't have one, although I probably should with a second Megane. They never failed, though, only minor usual stuff.

All sorts of OBD systems do not access the brakes. OBD is for emissions only. Everything else use proprietary protocols.

[cyclonebri1]

Thanks Alex again, however I may have the issue resolved now.

Good news is, and this reinforces what I've always said about getting a relationship going with a decent non affiliated local garage, inspite of what I have read re the abs not being able to be read from the main ecu, it can be.
With there more advanced gadget than my standard scanner it showed all sensor circuits open, remember I had opened all connections and these had locked in.
Cleared and no lights on when stationary, took a quick drive and at about 20mph the lights back on.
Back to garage within 2 mins and connected up again and shows a duff LHS front sensor, must be missing the output when rotating, the test I couldn't get a reading from.
So, new sensor ordered and we will see.

Now the good news, I've only ever used these guys for the tests on our 2 cars, but the charge for the diagnostics and to clear the system when I've replaced the sensor was £20

[AlexB]

Very good! What scanner did they use?

[cyclonebri1]

Very good! What scanner did they use?

Didn't ask Alex, was too grateful, but when I have fitted the new sensor that is now on it's way, I will ask and report back.

[ikhan]

Just for information, when the ABS light comes on, it should clear without having to reset the ecu once the fault has been rectified. I know this because my front passenger side sensor came undone and when refitted, the wheel was only turned slightly with the engine running (during refitting the wheel, car still on the jack) and the light went out as soon as the ecu received a reading.

[cyclonebri1]

Just for information, when the ABS light comes on, it should clear without having to reset the ecu once the fault has been rectified. I know this because my front passenger side sensor came undone and when refitted, the wheel was only turned slightly with the engine running (during refitting the wheel, car still on the jack) and the light went out as soon as the ecu received a reading.

I think under normal condition what you say may be true, BUT, if the sensor is disconnected at the wiring plug behind the wheel arch shield, or at the abs ecu, then it locks in the fault and warning.

Anyway, the wrong sensor was supplied, that was exchanged yesterday and the new one will be fitted this morning, if the light goes off I'll let you know.