cruise Control

Don't know if it's related, but I have always replaced all four tyres at once with permanent four wheel drive vehicles. Check that there isn't too much difference in tread depth front and back. If the depth is too different, the centre diff will be operating all the time, not just when turning. No idea if there is a sensor there, but if so I imagine it is confusing the ECU.

Stuart

Can't think of a connection, the cruise switches on a TD5 only connect to the ECU as the engine is totally "fly by wire".

You have checked the main on/off switch on the binical is on haven't you? I can't remember if the tell tale in that switch is fed from the ECU or from the switch, I have a 70/30 feeling it's the ECU. If so the tell tale coming on means the ECU thinks it should be using cruise. Oh and cruise doesn't work below 30mph either...

Check the plug hasn't fallen off the back of the binical switch, it just pulls out. Getting at the steering wheel switches is not so easy as you have to take the small bomb (airbag) off the steering wheel. IIRC it's only 4 torx screws but you do need to take a couple of few precautions first.

The centre diff on a landrover has a 60/40 bias IIRC, I forget which way however.

No - the majority are 50/50. Only the latest may be.

That had me wondering for a minute, thinking, did they use a different number of teeth for either side of the diff on the output shafts?, didn't think so.

Martin

I think he's talking about the nancy-boy cars like Freelanders and modern Range Rovers..

... and 60/40 would be a torque split not a speed split anyway, so having no bearing on this subject.

The cruise control gets its speed signal from the SLABS ECU which suggests that the wheel speed sensors provide the signal. In that case I'd expect the speed signal to be an average of the four wheel speeds. Different wheel rolling circumferences will obviously affect that but not in a major way nor disable the system.

I suspect that the link to the tyre change is completely coincidental. If a wheel speed sensor connection was accidentally disturbed there would be other indications so it seems reasonable to rule that out.

I think a bit of electrical troubleshooting as suggested by Dave should be your starting point. The main relay provides the supply to the CC master switch. The master switch warning light only illuminates to indicate that the CC has been activated (CC master switch operated) not that it has been engaged. 'Is that warning light operating' should be the first question.

Is this an auto? It seems that CC only operates when in drive - new to me, I'll have to experiment, but it might explain why I've sometimes thought that my CC wasn't working

Like the ABS not working. If that system gets upset you have a veritable christmas tree of warning lights come on as TC, HDC and ABS all use that system.

Well that seems logical and safe to me. You don't really want your cruise to take you straight back up to 60mph the moment you pop it back into D... In a manual touching the clutch or brake will also turn off any set speed, you need to use the REStore switch to go back to the set speed.

This does throw a few more switches into the equation that might need checking.