I found out, on a trip two weeks ago, that the cruise control is not working on my 2001 P38 DHSE [BMW diesel].

I have read quite a lot of stuff relating to various issues, mostly the pipework leaking air. My question is - where on earth is the solenoid jobby that is possibly located under the bonnet ? This is a UK car, not a USA model.

I looked at a couple of pictures, which I think are of the V8, and they appear to show that it is right behind the EAS compressor box.

Not in my diesel model, it isn't.

So I thought that it could be behind the battery, but no, it isn't there either.

I have the buttons and switches on the dashboard for CC so I am pretty sure that it is fitted.

I looked through Section 19 in Vehicle repair, in RAVE, and although the manual explains how it works it doesn't show any diagrams about where the various modules are. I saw on diagram on a very old post, on another forum somewhere, that pointed to the ECM and the TCM being under the panel above the drivers knee,

But nothing, anywhere that I can find, about where the vacuum thingy is.

Maybe someone can point it out as I would like to check the vacuum pipe, just to see if it is OK.

Pierre3.

The diesel doesn't work like that. This post may help explain, but you won't have the vacuum pipes etc that the v8 has.

https://rangerovers.pub/topic/2135-cruise-control

Thanks for your reply, Brian. I had a vague suspicion, while I was looking this issue up, that diesel engines use a different method of CC.

I think that I will just leave it as I can't really find much about sorting it, and, unfortunately, I don't have a Nanocom. It isn't really a big deal, I would have liked it to work, but I am quite able to keep my right foot at the same postion all day, if required !!!

Pierre3.

The Clutch (if its a manual box) and brake switches both play a part in it. If either fails in the right way, you won't get it to engage. Looks like looking at Rave (page 304 of 1361 if your looking at the same version as me) that you have 2 circuits on the brake switch, so it may be possible to test that with a multimeter if you have no other way to access it. I can't see much other info on the cruise for the diesel, though I think its somewhat simpler than the v8 setup simply as you don't need something to pull the throttle open as its already electronically controlled so most of the bits used by the cruise other than the swtiches are part of other systems anyway?

I don't know if the diesel will speak to normal obd diagnostics if you have anyone that can do that (for the engine only) but theres a few on here that may be able to confirm that. That may be enough to point you in the right direction if its a failed part like the switches?

Brian, thanks for your reply. I have a feeling that te CC on the diesel is a purely electronic system. I'm beginning to think that the accelorator peddle gives a signal to the BeCM, which then controls the engine speed. When you press the CC button on the steering wheel the BeCM keeps the engine running at the selected speed. That's my take on it, anyway.

I won't bother trying to fix it, at this stage, but I will just check it again when I am next on a motorway.

Pierre3.

The diesel is fly by wire, the pedal sends a signal to the engine ECU, when cruise is on a signal is sent that simulates you holding the pedal down but adjusts if the speed changes due to going up or down hill.

Hence the most likely failure would be the brake switch? Given it sees a lot of operation!

Having looked through the i/net and using the query for BMW 2.5 cruise control I came across a webpage that pointed to the Electrical repair section in RAVE. Section B5.

There is a full description of the CC operation, and a Problem Solving schematic. However, I was correct in my suspicion about the system being completely electronic.

Pierre3.

Pull out the lower cover under the steering wheel. Big one with 4 screws.
Reach up under the dash to the right of the steering wheel and find a squarish shaped relay looking thing and unplug it. Then plug it back in. Mine didn't work until I did that.

It's clipped onto a metal rail.

Hi Tanis8472, sorry, I missed your post. I will give that a try once the rain has stopped.

One thing - does that relay jobby work with the diesel engine, or is it the one for the petrol V8 engine ? I know that the two systems are quite different in the way that they work, and my car is a diesel.

Pierre3.

So is his if you look at his sig.

Hi, Richard, yes, I missed that !!!!!!!!!!!!!!!!!!! I need new glasses.

Pierre3.

Yep. Electronic not vacuum operated.