Hi everyone.

Today I decided to ask technician Google about what could be causing the cruise control to cut out only at speeds over 32-ish mph.

It's been like this since I bought the car two years ago but I never paid it any mind until today... as google tells me it could be indicative of other problems... such as a vacuum leak?

The car is a 2005 S-Type 2.7L Diesel with 40k miles done.

Cruise Control works fine at 30mph, even pulls up hills, is totally fine with me overriding it with manual pedal movement, disengages fine when brakes are touched. I can also use the + and - signs to increase and lower speed (so long as it is below 32 mph) and the resume function works too.

The problem comes over 32 mph (or perhaps closer to 40mph). If I turn it on at this speed or higher it pulls the car on its own fine for a few seconds but then suddenly conks out with 'cruise control unavailable'. After this happens the cruise control cannot be re-engaged until I turn the car off and on again. Manual control of car is perfectly fine afterwards too.

Basically this means I can't cruise at cruise speed (70mph). I've installed iron weights in my shoes to compensate.

There is no check engine light but there was a gearbox fault a few months ago (hasn't reoccured since).

I'm not in dire straits to get this fixed but if it is indicative of a problem that can escalate then I'd want to get it checked out.

Thanks for any help .

 

I don't recall ever hearing of this problem but you should realise it may well be specific to the diesel and they were never sold in USA/Canada etc so almost no-one on here has one. Try the UK forum

 

Oh, I will try the UK forum