Wheel speed sensors

Scuzi · 18 Aug 2020 at 13:46

I’m trying to figure out if my local Merc specialist is milking me. I’ve been loyal to them for a while now but they recently replaced a rear brake line, which on reflection I’m not convinced needed to be done. Throwing in this I’m now beginning to doubt them.

Car is a 2010 Mercedes R350L CDI (W251).

3 years ago the NS rear wheel speed sensor failed. The symptoms were a short period of ABS/ESA going mental followed by the failure lights on the dash. After restarting the car this would clear and it would randomly occur again later.
They diagnosed a failed wheel speed sensor and replaced it.

Fast forward 3 years to today. I have the exact same symptoms. A random spurt of ABS or ESA going mental followed by them failing and disabling until the car is restarted. I called the garage and they have told me that all 4 wheel speed sensors need to be replaced at a cost of £680. I queried the previous replacement of one sensor which resolved the problem and got a reply along the lines of ‘the updated part numbers need to match’.

My bull****ometer is going ding ding ding. What do you think?

Also, is a wheel speed sensor an easy DIY job? I’m confident spannering motorbikes but have little experience on cars.

Haze · 18 Aug 2020 at 14:04

Never heard of 2nd opinions? Take it to another garage

Will Gill · 18 Aug 2020 at 14:07

abs/speedsensor replacing takes 10 minutes on my car, a quick google suggests the same for yours.

grudas · 18 Aug 2020 at 14:42

Will Gill said:
abs/speedsensor replacing takes 10 minutes on my car, a quick google suggests the same for yours.

usually is the case with most cars.. one screw/bold and a plug.

jsmoke · 18 Aug 2020 at 14:47

About the easiest job you can do. Unscrew/unplug and refit.

paradigm · 18 Aug 2020 at 14:57

jsmoke said:
About the easiest job you can do. Unscrew/unplug and refit.

Kind of. The MX5 was a royal PITA because they always rust-weld themselves on and typically need drilling out. It "might" be an easy job (especially for the one replaced 3 years ago), but the others might put up a fight.

Scuzi · 18 Aug 2020 at 14:58

Haze said:
Never heard of 2nd opinions? Take it to another garage

I’d rather get an opinion from the comfort of my own home before going to the inconvenience of driving the car to another garage and paying a diagnostic fee. Thanks for your contribution.

Will Gill said:
abs/speedsensor replacing takes 10 minutes on my car, a quick google suggests the same for yours.

Thanks. The part seems to be about £40 so if it was a 10 minute job it’d be a no brainer.

paradigm said:
Kind of. The MX5 was a royal PITA because they always rust-weld themselves on and typically need drilling out. It "might" be an easy job (especially for the one replaced 3 years ago), but the others might put up a fight.

I’ve been down that road before. Trying to save money but ending up spending twice as much and getting busted knuckles as a bonus! That’s the judgement I’m going to have to make now.

InvaderGIR · 18 Aug 2020 at 15:10

If you know the price of them and you're confident enough with a spanner and have a jack and stands it's probably worth inspecting them yourself to see if it's going to be a ballache of a job or not. Then you can go from there if you feel it's worth DIY or taking to a second garage.
You may not even need a jack and stands to inspect their locations and ease/difficulty of removal.

Greebo · 18 Aug 2020 at 15:15

Whats the garage labour rate? Plus there will be a stupid markup on the £40 sensor as well.

Its like my VW Touareg. It went in for its annual service and the video they sent me showed it needed new front pads and discs with a tick box to say I was happy for them to do it at £960 for the pair!!!!

I bought the parts for £280 and then it was a couple of hours labour at the local garage. A lot of people will just click yes and get it done.

So true cost was around 40% of what they wanted to charge.

Will Gill · 18 Aug 2020 at 15:23

If your car keeps munching them check the hub splines for corrosion or dirt build up

InvaderGIR · 18 Aug 2020 at 15:28

Will Gill said:
If your car keeps munching them check the hub splines for corrosion or dirt build up

Imagine if they are just dirty and need a clean...

Will Gill · 18 Aug 2020 at 15:39

InvaderGIR said:
Imagine if they are just dirty and need a clean...

Impossible, nothing on my car is free to remedy

Gaygle · 19 Aug 2020 at 13:20

Yeh it's an easy DIY job.

Did the garage tell you which sensor had actually failed? I don't claim to be a Merc specialist but this is the first I've ever heard of part numbers having to match for wheel speed sensors.

Iamzod · 19 Aug 2020 at 13:32

Is there anything you can download and use an OBD reader with to read the wheel speed outputs?

For example with Ford I use Forscan on my phone & I can see the live data from each wheel, so it's just a case of plugging it in & driving to the end of the street & seeing which wheel speed sensor graph is flatlined at 0mph, job sussed, 10 minute job to replace it. Or if it's intermittent go for a longer drive & leave it running whilst logging data.

Django x2 · 20 Aug 2020 at 20:13

Gaygle said:
Yeh it's an easy DIY job.

Did the garage tell you which sensor had actually failed? I don't claim to be a Merc specialist but this is the first I've ever heard of part numbers having to match for wheel speed sensors.

Nope, but is more than likely it might need to be coded, hence the part matching. And, if the issue has been persistent across this model, the original part may have been superseded by something more durable, hence the recommendation to replace all 4.

"andy" · 22 Aug 2020 at 00:41

It sounds very fishy that they need to match. I imagine it's just a hall effect sensor that either sends a signal back or doesn't. You can usually mix brands etc aslong as they send the right voltages back ! The only thing that might cause it to be more than a cheap job is corrosion but they haven't mentioned that and they can usually be cleaned up

My mum has had a couple of abs sensors on her 2015(I think) Slk. First one was done by mercedes and second one by a local ex merc technician who charged less than half the price

Gaygle · 23 Aug 2020 at 12:24

Django x2 said:
Nope, but is more than likely it might need to be coded, hence the part matching. And, if the issue has been persistent across this model, the original part may have been superseded by something more durable, hence the recommendation to replace all 4.

Again, I've never heard of any wheel speed sensor that has had to be coded. As @"andy" said, they are a simple hall sensor and the intelligent bit is done in the ABS/TC ECU.

Wheel speed sensors go bad every now and then, it's just an product of their placement and it doesn't sound like the OP has had huge issues with them. Even if it was as you say, you'd expect the specialist" to explain that to him. However the fact remains that nearly £700 four wheel speed sensors is daylight robbery. Your could half that price right off the bat by using the OEM ATE sensors, which I wouldn't be surprised if the mechanic did and never told the OP as even the Genuine parts are never marked with the brand stamp

Scuzi · 23 Aug 2020 at 19:38

Thanks all. Pretty much confirms my suspicions. Now to find a new garage! It’s a shame, as they used to be bloody brilliant. The guy who used to work on my car was a bit of an R Class enthusiast and he would talk me out of certain work rather than the other way round. I haven’t seen him the last couple of times so I assume he has moved on.

Any recommendations for a Merc specialist in the Southampton area?

Jonnycoupe · 23 Aug 2020 at 22:56

Can you read an error code to determine which sensor has the problem?