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Strange ABS issue

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ADK View Drop Down
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    Posted: 13 Dec 18 at 16:37
Hi,

The problem:
ABS live data is showing that the van is still moving even while it is stopped. When tested on a rolling road, the brakes work correctly. The ABS readouts show no faults. However, even when the van is completely stopped, the live data shows that the van is moving at 1.8km/h. The only symptom I have is a 'judder' in the couple of seconds before the van comes to a complete standstill when I apply the brakes.

The background:

My LT35 was in for a service recently, and I was told brake discs needed replacing, which the garage did.

I got the van back and straight away, I noticed that the van had acquired a fault:
1.when the brakes were applied
2.as the van was coming to a standstill
3. there was a 'judder' on the brake pedal.

It only happens in that second or two before the van stops completely and it happens every time.

I continued to drive it and at one point the ABS light came on briefly.

I took it back to the garage, they agreed that the symptoms described were present and after investigating, told me that an ABS sensor had probably been damaged or moved during the brake disc replacement as it was showing a fault on the ABS readout. They replaced the sensor and have phoned my to describe the situation as laid out in the first paragraph above. They also tell me that the 'judder' has not been cured but suspect that it is related to the fault which tells the ABS that the van is still moving.

I am yet to collect the van, which I will do tomorrow.

Any thoughts?

Because I don't know what to do from here. And I have no idea whether it is safe to drive!

Thanks in advance for any input.

Lancashire
LT35 80kw TDi - 2005
MWB/Hi-top
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mojo View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote mojo Quote  Post ReplyReply Direct Link To This Post Posted: 15 Dec 18 at 06:10
If replacing the sensor hasn't fixed it, then it's more likely they've damaged the wiring to the sensor.
Did they give you the abs fault code?
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tellytubby View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote tellytubby Quote  Post ReplyReply Direct Link To This Post Posted: 15 Dec 18 at 18:47
The symptoms are similar to a common Saab problem which is corroded reluctor rings ( the cog thing on the driveshaft that the abs sensor points at ).

As the teeth on the ring wear out the abs sensor gets less signal especially at low speed so you get an abs activation just as you pull up.

Could be something to look at - also check the abs sensor is in correct location if too far away youd get same sort of thing.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ADK Quote  Post ReplyReply Direct Link To This Post Posted: 16 Dec 18 at 15:04
Thanks very much for the replies, they are appreciated.

Originally posted by mojo mojo wrote:

If replacing the sensor hasn't fixed it, then it's more likely they've damaged the wiring to the sensor. Did they give you the abs fault code?


Thanks for the idea about the wiring, i hadn't thought of that. And they didn't provide any fault code - at this point in time, apparently there are no faults showing on any of the sensors. The only 'fault' is that the ECU is showing the vehicle moving at 1.8km/h when it is stationary.

Originally posted by tellytubby tellytubby wrote:

The symptoms are similar to a common Saab problem which is corroded reluctor rings ( the cog thing on the driveshaft that the abs sensor points at ).
As the teeth on the ring wear out the abs sensor gets less signal especially at low speed so you get an abs activation just as you pull up.

Could be something to look at - also check the abs sensor is in correct location if too far away youd get same sort of thing.


Excellent - thanks for the information. I did hear from the garage late on Friday and they had come up with the reluctor ring as a possible problem, so they've ordered one and will be fitting it tomorrow. I have done a bit of a crash course on ABS systems so I did a bit of reading and as you mention, it is not an uncommon problem. The fact that it occured at the time they worked in that area is my only reservation.

One detail i got wrong was that they had changed the hub seal in that area, not the brakes.

As for the distance to the sensor, is that the air gap? I did some reading and mentioned it when I spoke to the garage and they told me they had checked the air gap and it was fine.

The other thing I've come up with as a possible issue is uneven tyre pressure, so I will mention that if the reluctor ring doesn't cure it.

Thanks very much for all input, I'll provide an update when I have mroe information.
Lancashire
LT35 80kw TDi - 2005
MWB/Hi-top
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Post Options Post Options   Thanks (1) Thanks(1)   Quote ADK Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 18 at 11:59
...and the problem has been solved. It was indeed the reluctor ring.

It was the tiniest dent in the surface of the ring. It wasn't visible, it was something you had to feel by running a thumb over the surface. Difficult to believe but that slight distortion in shape was enough to trigger the ABS.



New Sensor



The old ring


Thank you for all replies.


Lancashire
LT35 80kw TDi - 2005
MWB/Hi-top
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mojo View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mojo Quote  Post ReplyReply Direct Link To This Post Posted: 23 Dec 18 at 20:31
Thanks for the update, glad your sorted.
2006 LT35 TDI 109 AVR
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