Tyres are the No1 suspect.
Presumably this has been a problem since the tyres were fitted?

If not the tyres then it must be the main ECU like the guy in Norway/Denmark but ECU's are USUALLY extremely reliable unless there is a well known software issue which can usually be address with a software update alone.

The tyre pressure monitoring was just for background info. I think BMW tried and subsequently replaced this system. Beauty was no additional sensors.

Stuart

 

Well, Car in today. All sorted out.

They took the front wheels off a stock used SLk and with the 205/55 ones on the cruise worked perfectly up to 80mph and above, ahem! It appears the tolerance on the ECU is about 1.5mph before the safety circuit cuts the cruise out. Wow, how sensitive is that then!

My SLK doesn't have the tyre pressure warning stuff, but now I'll have to go and push the dealer into putting the legally correct tyres on. 205/50 is not an approved fitting, and what's more, the back tyres are 225/50 WR16s instead of the approved VR16s, so they are also wrong and illegal. Oops.

I do love the car to bits though, so we'll sort something out amicably no doubt.

Thanks for the help.

 

Glad you are near to getting sorted.
However some things which still don't fit.
What about.....The fact that the Cruise didn't cancel when you touched the brakes?
and................The ABS, ASR and ESP were working OK. I find it very hard to understand how the ESP could work correctly since this system needs to monitor "slip" between all 4 wheels relative to one another continuously. Maybe the circuitry just zero bases everytime the system is started but if so I wonder why that strategy isn't used on the Cruise. Mmmm.
Need to think about that a little more.
What codes were present....I'd like to know in order to learn more.
Did you glean anything else from the dealer?
What did they say when YOU pointed out that the tyres were wrong?
Who fitted the wrong tyres. If it was the dealer then there should be no trouble exchanging them!
Don't worry about the W R16 vs V R16. The W is a better qwuality tyre (W is a higher vs V constant speed rating code).
W is not OE listed because being better it is more expensive therefore not OE.
Glad to have been of assistance.
Thats twice I've now encountered this type of problem so it must be more common than one would think. Check tyre size number 1 on the check list!!
Even the manufacturers Ford and Mercedes don't seem to be switched onto this one UNLESS of course anybody knows to the contrary...and I'm sure someone will.
Stuart

 

Cheers, Stuart. I'll leave the rears on then.

The dealer didn't tell me if any codes have appeared, but the technician implied none had. I know the ASR works because I've tried it on the wet roads having fun, ditto the ABS which I coaxed into working deliberately least week. Dunno if the ESP did anything as it was a straight line stamp. My last car was a Saxo and Citroens have somewhat more sensitive brake pedals, and that weird feeling hasn't appeared again. Thanks again for all your help and tips, hopefully it will be all fine for me from now on and I can enjoy owning my car. I've at least had the roof down several times already, and I like the way it warms up quickly and keeps my feet warm driving in November with the roof down!

Best wishes,

Mark.