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Discovery 2 TD5 52 reg. Cruise Control


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The cruise control on my subject Discovery has stopped working.

The light on the dashboard switch glows when the switch is switched on.

I have read a lot on this forum about a split vacuum hose being a possible cause.

I have been told by a non forum source that my model Discovery does not have a vacuum hose in the system.

I'd be grateful if someone could give me a definitive statement as to whether or not a vacuum hose will be incorporated and, if so, where it can be found.

Very many thanks in anticipation of any help.

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it's deffinitely electronic, no vacuum involved, first suspect is the brake switch, it has a NC contact which used to fail, push the pedal fully down and pull the plunger of the switch untill it meets the pedal to rule out a missadjustment, if it's manual the clutch switch or it's circuit can be suspect too...these are to most common issues but it could be electric too... these switch's inputs are covered by diagnostics if you see what i mean

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Thank you bear & sierrafery.

I very much appreciated your comments which both point to the cruise control being electronic.

bear - you mention fuses? I can only identify one fuse, located under the steering wheel and which is ok. Are there more which I've missed?

sierrafery - re. the brake switch (which I can see when the fuse box cover under the steering wheel is dropped down), that appears to be working ok.

What does NC mean, please?

The vehicle is a manual - but there is no similar switch on the clutch pedal.

A non-forum contact has said that it could be a faulty ECU causing the cruise control to fail?

I see from the vehicle handbook that the fuse that I have checked (and is ok) protects the Cruise Control / Electric Mirrors / Screen Washer - rear / Diesel ECU.

What is the Diesel ECU, what is it's function and could it be the cause of a failed cruise control?

If so, would it be expensive to repair?

Thank you for your ongoing help.

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NC means normally closed, it's a contact used only by the management and you can't see if it's working or not only with tester cos the brake lights are working on the NO(normally open) contact, the only symptom might be some power loss at low speeds but it could be not noticeable depending on the fuel map used,when the pedal rests the NC contact must be closed or the cruise controll will not work, as about the clutch switch, i'm not very familiar with this "XX Reg" things but if your D2 is facelift the clutch switch is attached to the bottom of the clutch master cylinder, if not it's like in the attachment... the best would be to check both switch's inputs with tester cos there might be problem with theyr circuit too not necessarily with the switches... see attachments an you'll understand what i mean, if these are ruled out then you can think of more complicated things like ECU fault

post-24079-0-09728000-1412880211_thumb.jpg

post-24079-0-55304100-1412880230_thumb.jpg

post-24079-0-86946700-1412880252_thumb.jpg

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Is the horn working? The CC uses the same relay as the horn (R13) in the fuse box in the engine bay. I realised that when my CC stopped working after I swapped my horn relay over to operate my fog lights.

:i-m_so_happy: ... that's a brilliant ideea, i completely forgot about that, yes the horn relay is deffinately involved

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by the way, now as you know more about these, i said that brake switch adjustment thing in my first post cos if you watch the drawing i made with the pedal and the plunger you'll see that if the plunger is not pulled completely out to reach the fully depressed pedal it might not be pushed up enough by the released pedal to close the NC contact if you see what i mean, that plunger has a kinda ratchet so it can move without moving the contact so better do that adjustment to rule it out, it's something which happens that's why the adjustment procedure is described in the manual too...you have to pull hard enoug to hear it clicking if it doesnt touch the pedal from the beginning

Switch - brake light

The brake switch is set automatically during fitment.
If the setting is disturbed, the switch can be reset by
depressing the brake pedal and pulling the plunger
out of the switch body, until it contacts the pedal.
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bear, sierrafery, Shackleton & rovernut - thank you all very much for taking the time to offer such comprehensive advice.

I now need a bit of time to assimilate all that you've told me and hopefully resolve my problem.

Thank you again for your efforts.

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  • 8 months later...

Hi,

TD5 Automatic. Found your posts very useful and informative. My CC was not working. Checked the brake switch with Lynx Diagnostics. All CC switches were functioning. The brake switch only showed one circuit working when brake depressed. I have changed the brake switch and the new one shows both circuits working. NO and NC both show ON when pedal is depressed and OFF when resting. Is this correct? Looked at ECU which seems to be fine. Also no faults recorded on Lnyx. Cruise control is still not working. Could it be a broken wire someplace?

This is my 1st post here. Bought my 1st Discovery last year and very pleased with it. 2001 TD5 7 seater which regularly travels back and forth between England and Germany and up and down mountains when the wife is away :-)

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If the light comes on on the main cruise switch and the brake switch and circuit seem fine then there's not much left but the steering rotary coupler and wheel switch gear. I'm going on memory here but the main switch energises the CC circuit, after that the wheel switches send signals to the ECU to set the speed/cancel it. Unless the car has been badly attended to in the past a bad wire is unlikely, so test for continuity through the rotary coupler.

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