Wheel speed sensor? Advise needed please

[enuff_zed]

Yesterday I fitted new front callipers, new discs and new pads to wifey's 2.5i.
I did quick swaps of the callipers, with minimal fluid loss and bled them with an eezibleed. At no point did the reservoir level drop more than about 5mm (I'm paranoid, so I kept checking that).
Went for a test drive and the brakes are great. Bedded them in and they work perfectly.

However, I very quickly got an array of yellow lights. Handbrake, DTC, ABS and flat tyre. Tyre pressures all spot on and fluid still full.
Checked the codes - left front wheel speed sensor. Reset, took it for a run and they all came back. Again the only code is left front wheel speed sensor.

So today I took out that sensor and indeed I found a small amount of iron filings stuck to the side of it, not the tip. I cleaned it all off and put it back together.
Test run, same lights and same code!

Everything was perfect before I started. Ironically it was the front right calliper binding so it was only my ocd that disturbed the left at all. Dammit!
However, that calliper was looking pretty corroded too, so needed doing.

My question to you all is............... is it possible for a perfectly good sensor to fail like that?
I did have to smack the disc off with a hammer, but I didn't hit anything else. Could the shock bugger up the sensor?

Or am I looking for something else?

Initial reaction is to buy a new sensor anyway, but not if it's likely to be another issue.

All help and suggestions appreciated. Thanks.

 

[-Tom-]

If you haven’t already, plug the suspected sensor on the right hand side, with a reset and make sure the fault then reads to the right. That should help rule it in / out as the sensor only.

 

[enuff_zed]

If you haven’t already, plug the suspected sensor on the right hand side, with a reset and make sure the fault then reads to the right. That should help rule it in / out as the sensor only.

Good idea. I assume they're interchangeable then?
I was randomly googling and I'm sure I saw some that said LH or RH?

Wifey suggested it was time to go to the indy, especially as it's due an MOT and he could fix it at the same time.
However, if his code says the same as mine I'm sure he'd recommend ruling out the sensor first, so I may as well do it myself!

 

[-Tom-]

Yes they should do. The loom could well be different lengths to the connector for the different sides, but for the purpose of just plugging it in to run the checks then it should be fine.

Had many hours of fun with an r55 mini ... :roll:

 

[enuff_zed]

Yes they should do. The loom could well be different lengths to the connector for the different sides, but for the purpose of just plugging it in to run the checks then it should be fine.

Had many hours of fun with an r55 mini ... :roll:

OK ta.
Now wrestling with the dilemma of disturbing the side I know IS working versus the cost of a new sensor for the left, on spec.

 

[-Tom-]

Someone please correct me if I’m wrong, but at risk of damaging a good sensor then leave the known working sensor in the hub, just unplug it at the connector and attach the possible faulty one. If the left sensor is at fault, you’d then have a reading of both fronts being at fault (as the left would be missing).

 

[enuff_zed]

Someone please correct me if I’m wrong, but at risk of damaging a good sensor then leave the known working sensor in the hub, just unplug it at the connector and attach the possible faulty one. If the left sensor is at fault, you’d then have a reading of both fronts being at fault (as the left would be missing).

Err? Given that it only throws a fault once the wheel starts turning, not fitting it would show a fault regardless, surely?

 

[-Tom-]

I’m probably not explaining it properly. I’d still be swapping them over. If the fault moves then a sensor is a nice cheap repair.

For reference when my left sensor was showing as failed, INPA showed it to be reading max speed whilst stationary. I swapped the front sensors over and the same fault still showed, on the left. From there I was then able to try a few other things that got it sorted.

 

[Chris_D]

Make sure you use contact cleaner to clean those sensors. don't use anything like wd40.
I had a lot of fun trying to wrestle one of those back to life not long ago! grr

 

[enuff_zed]

Make sure you use contact cleaner to clean those sensors. don't use anything like wd40.
I had a lot of fun trying to wrestle one of those back to life not long ago! grr

Hi Chris, I assume you mean the electrical connector end?
I haven't disturbed that at all so far, just pulled the sensor from the hub and cleaned it. I only used a cloth, without any cleaner on it.
However, I did use a fair bit of spray 3-in-1 on various bolts when changing the callipers.
The sensor had iron filings like a hairbrush on the side, but nothing on the front face.

Did you manage to sort yours, or buy new?

It just seems odd that it has happened during other work in that area, so I'm wondering if the shock of the hammer hitting the back of the disc was enough to rattle it into submission.

 

[Rucky]

It might not be the sensor - have a squint in the sensor hole and make sure the wheel is clean and has no debris trapped in it.
The sensor should not have iron filings on it ?

 

[enuff_zed]

It might not be the sensor - have a squint in the sensor hole and make sure the wheel is clean and has no debris trapped in it.
The sensor should not have iron filings on it ?

I did think that, but the deposits don't look recent. Could have been there years maybe?
I managed to cut down a stiff bristle brush and push it against the back of the hub, through the hole, while spinning the wheel. It came out clean.
I have ordered a new sensor anyway (always good to have a spare!), as I'm fed up with continually taking the wheel off, especially on my gravel drive! Plan is to swap it, combined with another bloody good clean out, then see what happens.

 

[Rucky]

I did mention on another post that my pattern sensors fitted were 1mm longer than the BMW ones but I only found out when one of the replacements failed after rubbing the toothed wheel !
you might wish to check length back to back when you fit just to be sure.

 

[enuff_zed]

I did mention on another post that my pattern sensors fitted were 1mm longer than the BMW ones but I only found out when one of the replacements failed after rubbing the toothed wheel !
you might wish to check length back to back when you fit just to be sure.

Yes I remembered reading that. I toyed with the idea of using a thin washer to space it out properly, but then thought sod it and bought genuine.

 

[enuff_zed]

I’m probably not explaining it properly. I’d still be swapping them over. If the fault moves then a sensor is a nice cheap repair.

For reference when my left sensor was showing as failed, INPA showed it to be reading max speed whilst stationary. I swapped the front sensors over and the same fault still showed, on the left. From there I was then able to try a few other things that got it sorted.

Ah, a light has come on! In my head, not another one on the dash. :roll:
So if i go to the car now and do a real time check while stationary there is a slight chance it'll show max speed rather than zero. In which case your swap plan makes sense. I'll give it a go.

What did your issue turn out to be?

EDIT: Just tried that and all four read zero. Wfh so when I get a break I'll run it up the road for live readings.

 

[BumpyZ4]

With the sensor installed unplug the harness and put an Ohm meter on it and spin the wheel. If the ohm meter readings don't move while the wheel is spinning the sensor is bad.

 

[enuff_zed]

With the sensor installed unplug the harness and put an Ohm meter on it and spin the wheel. If the ohm meter readings don't move while the wheel is spinning the sensor is bad.

Thanks, I'll try that too. All good ideas for furthering my knowledge of fault finding electrickery, if nothing else.

 

[enuff_zed]

Well [ref]BumpyZ4[/ref], I'm afraid I failed to follow your advice as the new sensor arrived and I thought, sod it, just fit it.
I did, and it worked!
The original was marked up 'BMW' on one side and 'ATE' on the other. My guess is that it's the original, 17-y-o, 100k miles on it. Hammering the old disc to unstick it from the hub was probably enough to kill it, just though the transmitted shock. Maybe the wiring was getting brittle and that was the final straw?
So now all I have to do is wash the car and hand the keys back to 'management'. Weather is supposed to be good here over the weekend, so she'll no doubt be in full Thelma and Louise mode.......................well, socially distanced Thelma anyway
I shall rest on my laurels and watch the rugby. :wink:

 

[-Tom-]

Good work! :driving:

 

[enuff_zed]

Woke up in a cold sweat at 3am, convinced I didn't remember taking the locking wheel nut adaptor back off the wheel.
Sure enough, at 7am this morning I found it 300 yards up the road, still intact!

Off to buy a lottery ticket now! :roll: