My first Mercedes maybe my last!

[LostKiwi]

Unless they are using STAR diagnosis it’s likely their computer is of no help.

Beat me to it!

 

[Razor4173]

Sounds like a rusted up reluctor ring to me. Wheel speed sensor in other words. That would throw cruise control and traction control off.

Ok thanks for the info i will.discuss with my garage.

 

[Razor4173]

Would agree with all the above, except that no symptoms occur until c.70mph is reached, and presumably the car drives nrmally on a restart until such a speed is reached again.

Puzzling ... could it be a bad connection on one of the wheel speed sensor leads that only shows up at speed? Vibrational? My experience is limited, but when I've had a speed sensor fault in the past and taken live readings while driving, the discrepancy shows up at any speed.

Can't see a yaw rate sensor being the cause, or the steering angle sensor, as at such a speed you are presumably not hammering the car round sharp bends, but driving in a straight line (yaw sensor on yours is under the passenger front seat carpet. Seat needs to be removed, plus door sill trim to get to it. Engine off, key out. Easy swap, and cheap.)

I would break and remake all the possible connections as the next step - including the multiplug on the Abs unit. Dry joints, if it is such, don't like vibration.

Does the autobox play up when this happens, or does it continue to change normally? I would expect it to short shift. You've come to the right forum - there are knowledgeable guys on here who will offer more help as they spot your post.

Hi yhanks fkt your reply the 5 speed auto box still works as it should and i dont rag the car. I am concerned as lots of different advkce already and could get expensive. Im out of pocket £2000 and have no confidence in car or garages ive been too. May have to call it quits and get ris of the car. Thanks anyway

 

[LostKiwi]

Hi yhanks fkt your reply the 5 speed auto box still works as it should and i dont rag the car. I am concerned as lots of different advkce already and could get expensive. Im out of pocket £2000 and have no confidence in car or garages ive been too. May have to call it quits and get ris of the car. Thanks anyway

Whereabouts are you?
Our trusted Indys (such as Steve) are VERY good and will definitely sort it for you.
There are several who regularly post on here who I am sure will be happy to sort it out for you.

 

[Razor4173]

Whereabouts are you?
Our trusted Indys (such as Steve) are VERY good and will definitely sort it for you.
There are several who regularly post on here who I am sure will be happy to sort it out for you.

Hi i live in Plymouth, Devon. Regards Alan

 

[LostKiwi]

Cole@MBS is in Southampton.
Steve is near Bristol.

I guess they're probably a bit of a hike but I am certain any of them could sort you out. Steve would probably be your best bet (and you'd have a nice long motorway run on cruise to test it out)

 

[umblecumbuz]

Still puzzling to me.
If this was wheel sensor, why does it only show up at speed?
And why does it reset at each restart?
Why is there no limp mode if driven under the 'trigger' threshold?

To me, this suggests that the fault lies elsewhere.
On a learning curve here.

 

[Naraic]

Losing cruise control at about 70 mph is typical behaviour for a bad speed sensor or mismatched tyres.

It could be that your tyres are correct...just excessively worn at the rear (usually). I have had this before on a w210.

One time I had a bad earth to the offset lamps and when I turned these on the CC would be upset. But that was a 210.

 

[JBell]

Hi i live in Plymouth, Devon. Regards Alan

Coverdale 2 in Newton Abbot, Lee has Star and is an Ex MB Master Mechanic, I don't take my car anywhere else

http://www.coverdale2.co.uk/

 

[Wighty]

If the possibility is tyre related , what about a set of matching tyres having been placed on the wrong size set of rims (wrong size of tyre for the wheel ) ??

 

[umblecumbuz]

Looks like my train of thought may be incorrect here, but this still looks like being caused by some other fault to me.

I always understood that, as each wheel sensor supplies the Abs module with a signal that will vary in both strength and frequency depending on car speed, any mismatch will trigger a fault code - and this is particularly sensitive at low vehicle speeds. Hence my puzzle when the OP stated that the fault only shows up at high speed.

The mismatch throwing limp mode could be a faulty sensor, broken or clogged reluctor ring, poor tyres or even worn wheel bearings - but in each case, the wrong signal will be received by the Abs unit at low speed as well as high. That's why I suspect something else.

No substitute for a Star diagnosis - in the hands of a good technician.

 

[LostKiwi]

Looks like my train of thought may be incorrect here, but this still looks like being caused by some other fault to me.

I always understood that, as each wheel sensor supplies the Abs module with a signal that will vary in both strength and frequency depending on car speed, any mismatch will trigger a fault code - and this is particularly sensitive at low vehicle speeds. Hence my puzzle when the OP stated that the fault only shows up at high speed.

The mismatch throwing limp mode could be a faulty sensor, broken or clogged reluctor ring, poor tyres or even worn wheel bearings - but in each case, the wrong signal will be received by the Abs unit at low speed as well as high. That's why I suspect something else.

No substitute for a Star diagnosis - in the hands of a good technician.

The difference in value increase with increased speed even though the percentage is the same throughout. If I recall correctly we had another thread some time back where someone had the incorrect tyres and it showed exactly the same symptoms.
A cracked reluctor will manifest at low speed as a signal goes missing for a short period of time hence the ECU thinks the wheel has locked and engages ABS to 'free' it.
A rusty reluctor could confuse the sensor as the pulse will become indistinct.
If the reluctor is rusty it needs totally cleaning out and the sensor needs to be cleaned as well.

We've had this issue previously - http://forums.mercedesclub.org.uk/index.php?threads/cruise-control-keeps-turning-off.86019/

In two of the cases it was definitely incorrect tyres.

 

[Craiglxviii]

I’m of the same recollection as you Alastair.

 

[Razor4173]

Hi all, many thanks for all your suggestions advice and help. I took the car back to the Mercedes specialist. The wheels and tyres were ckrrect and fitted as they should. They use the STAR computer system. Connected the car up and nothing obvious. They removed the flooring from under the car and loads of oil spilled out. There was a large tear on one of the rubber pipes which goes into the into cooler. The inter cooler was also leaking hence the lack of power makes sence hence the lack of power at speed and black smoke coming from thr back all the time (which i forgot to mention in my post, sorry). All being replaced on thursday at a cost of £464. To add to the £2000 spent already on electrical related faults. Thanks to everyone for tour help.

 

[Wighty]

Hi all, many thanks for all your suggestions advice and help. I took the car back to the Mercedes specialist. The wheels and tyres were ckrrect and fitted as they should. They use the STAR computer system. Connected the car up and nothing obvious. They removed the flooring from under the car and loads of oil spilled out. There was a large tear on one of the rubber pipes which goes into the into cooler. The inter cooler was also leaking hence the lack of power makes sence hence the lack of power at speed and black smoke coming from thr back all the time (which i forgot to mention in my post, sorry). All being replaced on thursday at a cost of £464. To add to the £2000 spent already on electrical related faults. Thanks to everyone for tour help.

Jesus buddy that's a rough ride with all the costs , but at least that should all be fixed now .

 

[Yugguy]

It's hard aye. I have had to spend a few quid on my 2008 c220 and lucky that some got paid by the warranty.

Sometimes I think should I have bought that much newer Astra which was a nice car and fully loaded.

But the Merc gives me a much better feeling when I drive it.

 

[umblecumbuz]

Glad Mr Star found your fault, and pleased for you.

Let's hope you'll now change your thinking about Mercs, and keep this one until the time comes to replace it with anothet.

 

[EmilysDad]

Glad Mr Star found your fault, and ......

It/he didnt ..... it just needed someone to have a proper look at the car. Diagnostic electrickery isn't the b all

 

[umblecumbuz]

It/he didnt ..... it just needed someone to have a proper look at the car. Diagnostic electrickery isn't the b all

Exactly.
As I said earlier:
'No substitute for a Star diagnosis - in the hands of a good technician.'

 

[JBell]

Hi all, many thanks for all your suggestions advice and help. I took the car back to the Mercedes specialist. The wheels and tyres were ckrrect and fitted as they should. They use the STAR computer system. Connected the car up and nothing obvious. They removed the flooring from under the car and loads of oil spilled out. There was a large tear on one of the rubber pipes which goes into the into cooler. The inter cooler was also leaking hence the lack of power makes sence hence the lack of power at speed and black smoke coming from thr back all the time (which i forgot to mention in my post, sorry). All being replaced on thursday at a cost of £464. To add to the £2000 spent already on electrical related faults. Thanks to everyone for tour help.

Glad you got it all sorted, bit of a pain in the arse but you will have a great car now