L6/3 Left rear axle rpm sensor has a mechanical fault

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dogday

Member
Joined
Oct 29, 2022
Messages
43
Location
Peak District
Car
Mercedes E220 cdi
New to this forum so hello.

Re: Mercedes W212 E220 cdi

The yellow ESP and ESP off and ABS warning lights are on with the message 'Run flat indicator inoperative - see owners manual'.
The icarsoft MB V.2 says 'L6/3 (Left rear axle rpm sensor has a mechanical fault).

Any idea what this fault points to? When it says 'mechanical fault' does this mean it's more likely the reluctor ring? If it was the sensor on the lead would the icarsoft scanner say something else? If it was the brake switch, as is often mentioned, would this show up instead on the scanner?

Thanks for any advice
 
Might be worth popping into an indie with Star if there is someone near. That should confirm the problem. As you say it could be a few things and although good the small scanners have their limits.
 
Any idea what this fault points to? When it says 'mechanical fault' does this mean it's more likely the reluctor ring?

Very much doubt the CarSoft would know if there was a mechanical problem with the reluctor ring , it maybe the case the reluctor ring has split and damaged the sensor , if that could happen on your car (happened to us with the boys Clio) .

I had similar with the Cayenne and the Carsoft pointed me in the direction of the rear ABS sensor , £26 (from Autodoc) and 45 mins later all was well again.

A quick test would be to unplug the one on the other side and see if you get a similar fault.

K
 
Very much doubt the CarSoft would know if there was a mechanical problem with the reluctor ring , it maybe the case the reluctor ring has split and damaged the sensor , if that could happen on your car (happened to us with the boys Clio) .

I had similar with the Cayenne and the Carsoft pointed me in the direction of the rear ABS sensor , £26 (from Autodoc) and 45 mins later all was well again.

A quick test would be to unplug the one on the other side and see if you get a similar fault.

K
Thanks for the replies. I have ordered a new ABS sensor from Autodoc for £14 plus postage. I have read that you should only use OEM sensors but this one is made by Ridex. If you go on their site they make big claims about all their equipment being made to OEM standards so here's hoping. If the new sensor does not cure the fault is it possible to view and clean the reluctor ring just by removing the wheel? I have seen a video of somebody removing the sensor and then poking a flat blade screwdriver through the hole to scrape any rust or dirt from the reluctor ring. This might also give a feel for any damage to the ring ?? Thanks.
 
When changing the ABS sensor, it's a good time to clean up round the reluctor ring.
I had one crack on a W210.
It caused all sorts of fault lights on the dash panel.
It was not easy to see the crack until the ring was removed.
Once changed, all the faults were cleared and did not come back.
 
When changing the ABS sensor, it's a good time to clean up round the reluctor ring.
I had one crack on a W210.
It caused all sorts of fault lights on the dash panel.
It was not easy to see the crack until the ring was removed.
Once changed, all the faults were cleared and did not come back.
Thanks for the reply. Rougthly how much would an indie charge to replace a reluctor ring? Thanks.
 
Thanks for the reply. Rougthly how much would an indie charge to replace a reluctor ring? Thanks.
Mine did the NSF on my C Class back in 2019. Not sure about your W212 but on the 204 the reluctor is built into the wheel bearing.
Bearing kit was £90 and 2.5 hours labour (including diagnostic and road test) £165
 
I know this is a very long shot but the tyre to the wheel in question is at it's wear limit so will have a very slightly reduced diameter and hence a slightly increased rpm compared to the other wheels. Has anybody had the fault cleared after changing a tyre ? Thanks.
 
I know this is a very long shot but the tyre to the wheel in question is at it's wear limit so will have a very slightly reduced diameter and hence a slightly increased rpm compared to the other wheels. Has anybody had the fault cleared after changing a tyre ? Thanks.
I guess anything's possible, but in that case I'd have thought that resetting the TPM would make the error go away. Or maybe not.🤔
 
There are a lot of comments about the brake light switch potentially causing ABS errors. Surely if the brake lights come on if you press the pedal then the switch is OK and wouldn't the icarsoft scanner show up any brake light issues?
 
There are a lot of comments about the brake light switch potentially causing ABS errors. Surely if the brake lights come on if you press the pedal then the switch is OK and wouldn't the icarsoft scanner show up any brake light issues?
I don't know about Mercs, but on a few vehicles the brake light switch has more than one set of contacts. The only real check is to whip the switch out and stick a meter on it.
 
I don't know about Mercs, but on a few vehicles the brake light switch has more than one set of contacts. The only real check is to whip the switch out and stick a meter on it.
Thanks for the reply. Surely if the switch is switching the brake lights on and off then a meter would show the same, or does the switch also switch something else other than the brake lights (need a wiring diagram)?

Another thought about a bad abs reluctor ring, if the sensor was OK but the reluctor ring was damaged wouldn't the icarsoft scanner show no fault ??
 
if the sensor was OK but the reluctor ring was damaged wouldn't the icarsoft scanner show no fault ??

Not if the ring has split and has damaged the sensor.

Had a fault with the boys Clio ,once reset the ABS fault light would only come on above a certain speed , it turned out the reluctor ring was cracked and at speed the centrifugal force would lift the ring enough to cause a misreading of the sensor generating the ABS fault code.

K
 
Not if the ring has split and has damaged the sensor.

Had a fault with the boys Clio ,once reset the ABS fault light would only come on above a certain speed , it turned out the reluctor ring was cracked and at speed the centrifugal force would lift the ring enough to cause a misreading of the sensor generating the ABS fault code.

K
Thanks Kenny.

In answer to the brake light switch, the icarsoft scanner will show an error reading if the switch is broken.

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Dozens of shops sell ABS sensors so these are clearly prone to problems. On Mercedes are ABS reluctor ring issues common or is it usually down to a bad sensor?
 
OK. So replaced ABS sensor, cleared error codes, car drove OK (stop start started working again) for about 100 feet at around 5 mph before same error code returned so looks like a new ABS reluctor ring is required ?

Please could somebody supply a tools list required for the job and a part number (and where to buy) a replacement ABS reluctor ring.

Thanks
 
Watching with interest, S212 E350CGI 2010, similar problems.
Bought Creader Elite, Benz edition, which shows rhs rear wheel speed sensor problem, might have been breaking down as I got the warning after hitting walking pace
Tried replacement sensor which I believe was doa as it was reading open circuit, waiting on a 2nd replacement…
Faults out with ign on immediately now so clearly not getting past POST check
New battery fitted as it was on original(no starting problems though).

Hoping it’s not the reluctor ring but rather that than the abs module….
 
Watching with interest, S212 E350CGI 2010, similar problems.
Bought Creader Elite, Benz edition, which shows rhs rear wheel speed sensor problem, might have been breaking down as I got the warning after hitting walking pace
Tried replacement sensor which I believe was doa as it was reading open circuit, waiting on a 2nd replacement…
Faults out with ign on immediately now so clearly not getting past POST check
New battery fitted as it was on original(no starting problems though).

Hoping it’s not the reluctor ring but rather that than the abs module….
This is the sensor that I purchased;

It was the cheapest they sold but they make many claims about being OE standard. After fitting I still have the original fault on my icarsoft scanner "rear left speed sensor mechanical fault". I then used the scanner to run a live test which shows all the wheel speeds. This showed that the other 3 wheels had near identical km/h readings but the rear left showed similar speeds except that the speed readings kept dropping by about a third. This showed the new sensor is working but something else is at fault. After reading, this type of error points to the ABS reluctor ring (which makes sense as a gap in the ring could cause these results).

I have now ordered a new reluctor ring (A2303570182) for £11. I'm guessing the job should take about 3 hours (clickmechanic says 3-4 hours to replace driveshaft so this sounds reasonable so long as nothing gets too stuck). The job looks well within the ability of somebody with a bit of spannering knowledge). You will need a few more specialist tools; 32mm 12 point socket for the hub nut, 18mm and 16mm spanners, a 12mm 12 point bit and 10mm hex bit for the control arms. I also purchased a torque dial for about £8 to add to the bar when tightening the hub nut (think about 320Nm). Most cheaper torque wrenches only go to 200Nm and one that would be required would be £100+ (just to do up the wheel nut!). There are lots of useful videos on youtube (couldn't find anything for W212 sensor ring replacement just W211 and W204 ring replacement which are very similar).

If I reset the error codes the warning lights would return just after reaching walking speed like yours.

As your new sensor was doa you might find the new one will work. Let me know how you get on.
 
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This is the sensor that I purchased;

It was the cheapest they sold but they make many claims about being OE standard. After fitting I still have the original fault on my icarsoft scanner "rear left speed sensor mechanical fault". I then used the scanner to run a live test which shows all the wheel speeds. This showed that the other 3 wheels had near identical km/h readings but the rear left showed similar speeds except that the speed readings kept dropping by about a third. This showed the new sensor is working but something else is at fault. After reading, this type of error points to the ABS reluctor ring (which makes sense as a gap in the ring could cause these results).

I have now ordered a new reluctor ring (A2303570182) for £11. I'm guessing the job should take about 3 hours (clickmechanic says 3-4 hours to replace driveshaft so this sounds reasonable so long as nothing gets too stuck). The job looks well within the ability of somebody with a bit of spannering knowledge). You will need a few more specialist tools; 32mm 12 point socket for the hub nut, 18mm and 16mm spanners, a 12mm 12 point bit and 10mm hex bit for the control arms. I also purchased a torque dial for about £8 to add to the bar when tightening the hub nut (think about 320Nm). Most cheaper torque wrenches only go to 200Nm and one that would be required would be £100+ (just to do up the wheel nut!). There are lots of useful videos on youtube (couldn't find anything for W212 sensor ring replacement just W211 and W204 ring replacement which are very similar).

If I reset the error codes the warning lights would return just after reaching walking speed like yours.

As your new sensor was doa you might find the new one will work. Let me know how you get on.
Ok so the company that sent the doa sensor apparently sent another over a week ago, hasn’t arrived so I went to GSF and bought a”better” one.that didn’t work and will be going back, btw it read0.75Mohms.
I tried the left rear in the rhs and got nothing, so cross wired the known good lhs sensor to the rhs socket and got a reading, verifying that the wiring was good. That sensor gave nowt mounted on rhs
So it looks like it’s the reluctor ring AND likely a new sensor too, local garage suggest getting one from euro car parts.
I’ll need to buy a few more bits from your list, thanks for that!

I’ll let you know how I get on…
 
Ok so the company that sent the doa sensor apparently sent another over a week ago, hasn’t arrived so I went to GSF and bought a”better” one.that didn’t work and will be going back, btw it read0.75Mohms.
I tried the left rear in the rhs and got nothing, so cross wired the known good lhs sensor to the rhs socket and got a reading, verifying that the wiring was good. That sensor gave nowt mounted on rhs
So it looks like it’s the reluctor ring AND likely a new sensor too, local garage suggest getting one from euro car parts.
I’ll need to buy a few more bits from your list, thanks for that!

I’ll let you know how I get on…

Ok so the company that sent the doa sensor apparently sent another over a week ago, hasn’t arrived so I went to GSF and bought a”better” one.that didn’t work and will be going back, btw it read0.75Mohms.
I tried the left rear in the rhs and got nothing, so cross wired the known good lhs sensor to the rhs socket and got a reading, verifying that the wiring was good. That sensor gave nowt mounted on rhs
So it looks like it’s the reluctor ring AND likely a new sensor too, local garage suggest getting one from euro car parts.
I’ll need to buy a few more bits from your list, thanks for that!

I’ll let you know how I get on…
Good to know it's not the wiring or module. I have purchased a ring for mine
GENUINE OE REAR MAGNETIC ABS PICK UP RING Fits MERCEDES BENZ E-CLASS W212 S212 | eBay

It looks to be an original genuine part with Mercedes part number etc on the packet. I found that the high street shops like Eurocarparts and GSF etc are very limited, and more expensive in what they sell and companies like autodoc (and ebay so long as you don't buy any unbranded items) are better for sourcing parts.

Ignore the torque dial on the tool list. This is only good for adding degrees to an already torqued component. I'm still trying a way to cheaply torque the hub nut without spending another £100 on a larger torque wrench?

I bought the tools from asta_tools_uk on ebay. They have 100% reviews, they were a good price, all the tools you need in one place, the quality looks very good and they delivered next day.

I hope to get on with mine at the weekend as long as the rain stops!!
 
Here's the results for my broken speed sensor. As you can see I accelerate to around 60 km/h, then should stay at that speed for a while before slowing back to zero. wheel speed graph.png
 

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