2012 SLK 250 R172 - ESP, ABS lights on

Kewickviper

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I bought a 6 year old SLK 250 a few weeks ago and within a week of buying all the warning lights for ABS and traction control started coming on. Initially they only came on occasionally, but now they're on all the time and also the parking break light occasionally comes on while driving. It had recently (August) been for a Mercedes service so I would have thought anything hidden like this would have shown up on the report had it been known before.

I bought a Creader VII+ scan tool and got a load of codes come up - some for internal issue with esp module, one about fuel intake not being clear and a bunch for components not getting enough voltage. I cleared the codes and drove around for a couple days to see what would come back. The eco stop/start function on the car hadn't worked since I'd bought it and upon lifting the hood I saw it still had the now almost 7 year old original Mercedes battery still installed. So I replaced the battery a few days ago and I now have the following codes which come on every time:

ME - Motor Electronics
- C003100 - The fault code is not found in the database.
- C003164 - The left front wheel speed sensor has a malfunction. There is an implausible signal.
- C003400 - The fault code is not found in the database.
- C003464 - The right front wheel speed sensor has a malfunction. There is an implausible signal.

Transmission
- D40A - The right front wheel speed signal from the traction system is not available on the CAN bus.
- D409 - The left front wheel speed signal from the traction system is not available on the CAN bus.

ESP(
drive.gif

- C110200 - The signal of component 'L6/1(Left front axle rpm sensor)' is implausible.
- C327100 - Implausible values of rpm sensors: speed at front axle.
- C111000 - Component 'L6/2(Right front axle rpm sensor)' has an electrical fault.
- C111700 - The signal of component 'L6/2(Right front axle rpm sensor)' is implausible.
- C110700 - The signal of component 'L6/1(Left front axle rpm sensor') is implausible.
- C120000 - The power supply for component 'B64/1(Brake vaccum sensor)' is not OK.
- C326600 - Consequential fault.

SRS
- No Fault codes.

VIN - WDD1724472F031686

If I reset the lights everything works fine until I drive a little way down the road, and then they all come on again. It seems odd to me that all of these sensors can go out at the same time so I'm thinking maybe it's some kind of connection fault to the ESP control unit, however I'm not sure where to start checking for that. What also seems strange to me is that if I go into the data stream function I can see that values are correctly being received on all 4 of the wheel speed sensors and also the brake vacuum sensor so I'm not sure what's causing these faults to flag up.

I've managed to find some abs sensors which are quite cheap from here: https://www.onlinecarparts.co.uk/ca...enz/slk-r172/7503/10138/abs-sensor.html#10110 but I don't want to go out and buy some before checking the connections.

I'm also worried about the fault: "The power supply for component 'B64/1(Brake vaccum sensor)' is not OK." does this mean I need a new brake vaccum sensor or just that the fuse/connection is faulty?

Any help would be greatly appreciated as I'm pretty new to any sort of car DIY.
 

LostKiwi

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Hi and welcome.
I'd check the connections to the ABS sensors and if ok try cleaning the sensor and reluctor, if that doesn't work change them. Personally I'd not bother with cheap generic sensors and only fit Bosch.
It's not unusual for wheel sensors to fail 'en masse' and one member here had all 4 replaced at the same time as they were marginal. MB recommend changing as axle pairs for this reason.
Even though you have a signal it can be a poor quality signal and this is what implausible refers to. If the signal is marginal it will flag it.
 
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Kewickviper

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Hi LostKiwi. Thank you v much for the advice. I'm going to take the front wheels off at the weekend and clean the sensors, hopefully resolves it if not I'm buying new sensors!

I'm also concerned about the - "The power supply for component 'B64/1(Brake vaccum sensor)' is not OK." message. I can't seem to find any parts for a brake vacuum sensor for R172 and have no idea where to check for the connections to make sure it's getting the correct power supply.
 

Flyinspanner

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Had similar warnings recently on the a-class, and it turned out to be the brake switch.
It’s like 2 switches, one side turns on the brake lights, the other sends all the signal to the ABS/ESP - I was actually seeing differing wheel sensor speeds at rest on my icarsoft!

Star diagnosed the switch ...£11.52 at MB, thirty seconds to fit, and all is good again.

It’s located on the brake pedal bracket at your feet.
 
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LostKiwi

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Try looking at the brake servo. At about the 4 o'clock position looking from the front for the sensor.
 
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Kewickviper

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Had similar warnings recently on the a-class, and it turned out to be the brake switch.
It’s like 2 switches, one side turns on the brake lights, the other sends all the signal to the ABS/ESP - I was actually seeing differing wheel sensor speeds at rest on my icarsoft!

Star diagnosed the switch ...£11.52 at MB, thirty seconds to fit, and all is good again.

It’s located on the brake pedal bracket at your feet.

Ah that's interesting. I had assumed the brake light switch was fine as no error codes came up for it. Did any codes for it come up on your icarsoft? Ideally don't want to replace something just for the sake of it, but if it might save me the job and cost of replacing both sensors then I'm willing to give it a shot.
 

Flyinspanner

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Can’t remember seeing it, but think I kinda jumped to immediately suspecting wheel sensors as they were flagged, and when I then switched to “live readings” and saw at standstill one wheel was reading 650kph, I mistakenly made it ‘fit’ the diagnosis for ESP/BAS issue. Luckily I decided to get it fixed at my local Indie, who popped it on star and gave me the good news (thanks Terry).
 
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Kewickviper

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Hi all thanks for your help. I replaced the brake light switch just in case but that didn't seem to fix anything so went ahead and replaced both sensors. All the lights have gone off now and everything seems to be working fine.
 


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