Technical Abs warning/bleeping

[Greyhound_Shrops]

Hello,

I am wondering if anyone out there can help me? I have a 53 reg JTD 115 ELX and am having some trouble diagnosing a problem with the ABS.

So far, I have replaced both front sensors. First the LH one was broken off at the hub. After replacement of this one a fault was still bleeping on startup. My laptop diagnostic software told me that the front RH sensor was not registering the speed of the car where the other three were.

I found that the RH sensor had its cable chaffed through having come adrift of its clip and come into contact with the alternator belt. I have fitted a new sensor today.

Back on the diagnostic which shows that the new sensor has made no difference - front RH is still not registering speed. However, the ABS function worked normally when I performed an emergency stop to test it from 60mph.

I have established that it is not the ECU at fault having fitted it to my wife's Multi (exactly the same part) where it works just fine. My car now has her ECU on it and the same problem persists.

Does anyone have any suggestions please?

Ian

 

[momoe]

Continuity test the cables back to the ECU, if this shows no faults swap sensors to eliminate these, (just in case one of the new ones is faulty).

You've already eliminated the ECU so that only leaves the rotor? that the sensors pick up?

 

[Greyhound_Shrops]

From some information that I have seen on another forum, it would seem that a cracked sensor ring could produce the symptoms that I have found. I believe that this is part of the wheel bearing so I will investigate that next.

Ian

 

[Greyhound_Shrops]

Now here is a puzzle. I have now had the front offside wheelbearing changed and guess what? A non-abs one was fitted that did not even have a sensor ring.

Now for the puzzle - after the work was done I drove the car and found the brakes were barely working. The pedal was almost solid and there is barely any braking unless the pedal was pressed very hard (as if the servo is not working). The car will stop but the back brakes try to lock up in the process. If it is braked hard from a reasonable speed (25+) then a pulsating can be felt as if the ABS is kicking in.

However - if either front speed sensor is unplugged (effectively simulating having the wrong wheel bearing back in) the brakes work normally again.

I have checked that the vacuum pump and the servo are working. I have swapped the ABS ECU with a known good one (from my wife's Multi and my old one is working fine on her car). With all sensors plugged in, there is no dashboard ABS warning and no error codes are generated.

Does anyone have any ideas?

Ian

 

[momoe]

Can you clarify a point? You say the new bearing does not have an ABS sensor ring, but also say that when you unplug the sensor this simulates having the wrong wheel bearing back in? Does the car have no ABS sensor ring on the front o/s or has this been replaced again with an ABS sensor bearing?

Assuming you've got ABS sensors on all corners, what happens if you remove the fuse for the ABS unit and try brakjing - just to confirm the fault is ABS related.
I'd also swap ABS sensors from your wife's car (front's) to see if the fault stays or moves.

 

[MultiPa]

Not sure if this is useful or not, but just in case:

I replaced both rear bearings on my Multipla a few months back, and although I ordered two ABS ones, and I got what looked like two ABS ones, it turned out that one was a non ABS one.

I assumed for a while that the ABS error was just a code that needed clearing as I didn't realise I'd fitted a non-ABS bearing - it looked identical to the other one, and came in abox with the same code on as the other one.

The braking performance was normal (apart from no ABS) - the pedal felt much as it always had. Occasionally the car would throw a wobbler and report an EBD error as well as an ABS error, but basically it was exactly the same except it had no ABS and the ABS warning light was on.

I don't know if the compter interretps data differently from the front and rear sensors though.

I suppose it's possible that 'no input' from the front means it assumes the wheels are locked, and so it releases braking pressure, but that would seem to be the 'unsafe' option. Fortunately I only had to brake hard once with no ABS sensor on the back of mine (car overtaking on a bend - nice) and I can confirm that it locked up at the back, but seemed not to at the front. (Not much fun going down a steep hill, on a bend, with a sleeping baby next to you - think on charging red BMW man on the A57 two weeks ago)

So, there you have it. Pretty sure that's not much help!

My theory is that somehow the system is interpretting the data from the new sensor as meaning that the wheels are locked, so the car is trying to release the braking pressure. I *think* the car treats the two axles seperately for ABS purposes (although this is based solely on that incident on the A57 when I was concentrating more on non having a head on crash rather than on being certain which wheel were locked and which weren't - pretty sure the back locked and the front didn't though) so this would explain the rear wheels trying to brake. You will only get the ABS pulsing at a decent speed because I think it only works above 10mph or so - could be wrong. I know when I finally got an ABS bearing for the back, the error code didn't clear until I got to 10mph or so.

If the computer is interpretting the data backwards (locked is unlocked, unlocked is locked) is it possible the sensor is wired backwards? Or could you disconnect the battery overnight and see if it resets?

Apologies if this is clearly the ramblings of someone way out of his depth!

 

[Greyhound_Shrops]

Hello,

Just to clarify, the situation is as follows:

I bought the car in February last year as a project. It had a failed turbo and had a few other issues, both mechanical and cosmetic - most of which I have sorted. The ABS issue existed at the time of purchase.

Bizarrely, the car passed its MOT in May last year. The tester missed the bleeping ABS warning for some reason despite my certainty that a failure was forthcoming.

This year, it has been failed because the warning is present. I brought the car home, investigated, and found/did the following:

1. Front LH speed sensor broken off at the hub - replacement fitted - fault code removed.

2. Front RH speed sensor cable had come adrift from its mounting and the cable had chaffed through - replacement fitted - fault code persisted.

3. Swapped the ABS ECU with the one on my wife's Multi - this made no difference and mine is working fine in her car.

4. The next logical step, since I knew the sensor and the ECU were OK, was to focus on what the sensor reads from as advised by momoe. The wheelbearing was replaced and it transpired that the old one was not the magnetic kind. With the new (correct) bearing fitted and with all sensors plugged in, there are no fault codes being generated but the brake pedal is almost rock hard (as if the servo is not working) and the back end tries to lock up when braking hard. If I unplug either front sensor, the braking returns to normal. I have tested the vacuum pump with sensors pluged in and unplugged and there is suction in both states.

5. The MOT garage commented that despite the bleeps and warnings about the ABS, the yellow dashboard warning light was not illuminating. On removing the instrument panel, I found that the LED which illuminates the warning light had its hole blocked up with a piece of black foam and some plastic presumably to try and cover up the cockup with the wheelbearing or pass a previous MOT.

At this stage, I believe that the only other major component I have not performed any physical checks on is the ABS pump itself.

Also, at momoe's suggestion, I have now driven the car with the ABS fuse removed. What I had was perfectly normal non-abs braking - clarified by a patch of gravel near the end of my street. This is definitely an ABS fault and, since it is the only thing left, my finger is firmly pointing at the ABS pump unit.

I hope this clarifies the situation. Any thoughts will be gratefully received

Regards

Ian

 

[momoe]

There is a possibility that the RH replacement sensor may be faulty, this needs to be swapped out to eliminate this (slim hope - but worth a shot).
Agree that the ECU appears to be ok, in which case ABS pump needs to be investigated.
I'm wondering whether the diagnostic software might give you an error code but given the notoriously flaky Fiat electrics, might be worth cleaning all the connectors associated with the ABS pump/ECU as well as the usual earth checks.

 

[richgarn79]

On some multipla's there is no visible evidence of an abs sensor pickup ring on the car. It is internal, but there, so be certain you are getting the right bits - it may appear there is the wrong part fitted but not necessarily true. The Vauxhall Zafira's are the same, all internal.