CLK cruise control problem- Please help

[reggie musson]

Can anyone tell me on my 2004 CLK 270 Diesel why my cruise control won`t stay on, for example, I set it to 70mph but as soon as I set it, the yellow outer ring lights on the speedo flash, and then the cruise is cancelled.
This started ever since I forgot to cancel the limiter before I switched the ignition off could this be a reason.
Please help, Reggie

 

[moonloops]

It's normally caused by wrong tyre sizes,or when a pair of tyres are new and others just about worn out.. not heard of issues with the cancel and ignition thing but I'm no expert..

 

[reggie musson]

It's normally caused by wrong tyre sizes,or when a pair of tyres are new and others just about worn out.. not heard of issues with the cancel and ignition thing but I'm no expert..

Now you say that both my rear tyres are about a month old and this fault has developed since changing them but there is some life left in both front tyres, so When I renew the fronts will this problem be corrected ?

 

[Sp!ke]

Did you get the exact same tyre size as your previous tyres?

 

[Stratman]

It's not unknown for a speed sensor wire to be dislodged when tyres are fitted.

 

[reggie musson]

Did you get the exact same tyre size as your previous tyres?

Yes at the moment the back tyres are diffrent to the front and will have the same all round once I get a few more miles out of them.

 

[andy27168]

Hi,
I think what Spike was asking were the new tyres exactly the same same size as the ones that came off? ie width and profile.
A lot of MB's have different size front and rear tyres, changing to a different profile can cause issies such as you are experiencing.

 

[panason1c]

Also, check tyre pressures, a tyre, or two, low on air will cause a difference in the rolling radius which could cause cruise to lock-out.

 

[panason1c]

It's not unknown for a speed sensor wire to be dislodged when tyres are fitted.

In that case, the abs light would be triggered.

 

[Stratman]

^^^^ It would indeed. Good point.

 

[jaymanek]

Ill bet they have fitted the wrong size?

Should be 245/40/17 rear and 225/45/17 front if you have the standard staggered sports setup.

 

[reggie musson]

OK your are all barking up the right tree, well done all of you, as when I had my rear tyres replaced the tyre fitter informed me the AMG wheels I have fitted to the car are replicas and are the same size all round, so he fitted, according to his data on his computer the correct tyres on the rear which are a lower profile and wider than before.
This means the front tyres are the correct width but are a different profile to the rear, so what I really need is the correct size AMG wheels for the front, maybe swap my wider front rims for some narrower wheels but feel finding someone to swop with will be very hard.
I had no idea all of this would have caused problems with the cruise control, although it`s OK up to 65 mph.
Big thank you to all of you and any more comments would be most welcome.
Reggie

 

[Stratman]

Th reason incorrectly sized tyres cause the cruise control to drop out is because the faster you go, the greater the rotational speed difference between the wheels. When it exceeds a set amount the cruise control microbrain interprets it as a wheel losing traction and therefore disengages the CC as a safety measure.

 

[GP801]

Can you not solve the problem by fitting tyres with the correct circumference?

 

[Rory]

... which are a lower profile and wider than before.

If they're lower profile but wider then it could be they're OK. Post up the actual sizes you've got front and rear.

The need to be near as dammit the same rolling circumference - you can compare them here: Tire size calculator

 

[reggie musson]

If they're lower profile but wider then it could be they're OK. Post up the actual sizes you've got front and rear.

The need to be near as dammit the same rolling circumference - you can compare them here: Tire size calculator

Thanks Rory yes I will when I have time.

 

[Aerialmark]

Th reason incorrectly sized tyres cause the cruise control to drop out is because the faster you go, the greater the rotational speed difference between the wheels. When it exceeds a set amount the cruise control microbrain interprets it as a wheel losing traction and therefore disengages the CC as a safety measure.

Thanks, that is exactly what mine is doing working uo to 50mph then dropping out and I have just had new tyres fitted on the rear and the fronts are nearly worn and ready to be replaced.