As I can see many of you are struggling with your cruise control. I have been fighting with this problem for months and since I cannot stand any of the toys on my 1997 Disco not working, I went through all the tests and checks and unnecessary replacements and finally got it going. My problem was lack of communication between VSS (Vehicle Speed Sensor) and the ECU (Electronic Control Unit). Now I am in the position to try to save you, my friends, time and money and hope for the best for you:
1) Do not replace anything before you make sure that you know what the cause of the problem is.
2) Start from the most common cause and the easiest to check.
3) First check the hoses to make sure there is no crack causing air leak. Find a Cruise Control Hosing Diagram and check them all. If not sure about their leak, replace them anyways, it is cheap. I replace them with fuel hose. To make sure of this, you will have to take the vacuum pump located in the opening bellow/ besides the jack. It is hard to take the vacuum pump out and put back, you have to use tilting and it is easier to unplug it first. There are three rubber “thing”s! sitting over three holes at the bottom, just pull them out.
4) Make sure there is no leak in the rubber puller on top of the engine, beside the accelerator cable. Disconnect the hose from it, using another hose suck and see if it retracts and holds.
From now on, you have to do your tests using the ECU plug, located under the glove box. To access the ECU, you have to tilt the glove box out all the way down. You do not have to unscrew anything. Open the glove box, on the sides and in the inside of the holes by the large springs, there are two wheels, just pull both up and guide them through the holes at the same time and the glove box will flap down making the opening behind it visible. It is hard to pull the wheels, but if you do not have strong grip, using the right tools, if needed, you can do it.
Once done, find the CECU, screwed vertically to a plate adjacent to a green box (I guess Alarm System Brain). Its plug is black and about 2 inches long. You have to unplug it, you may need to pull off the wire clip first. If you find it difficult to access the ECU, you can take the underneath cover off by pulling off the black plastic fasteners.
Now, following the numbers on the plug from left to right (from 1 to 8 on top and from 9 to 11 on the bottom) do the following tests carefully. I took this instruction off another site (I guess www.landroverresourse.com) which is more comprehensive than a similar instruction in one of the postings here:
Using a volt meter perform the following tests:

Ground Test - From pin 8 (black wire) on the cruise control module plug perform a continuity test to good chassis ground.

Main voltage test - With ignition & cruise control system on (on-off switch on the dash), transfer in high (non difflock) & auto box in 'drive' (you do not have to turn the engine on, just press the brake pedal and shift the gear) connect volt meter between pin 8 (black wire and if difficult, you can connect it to any ground) and pin 10 (white & yellow wire) you should have battery voltage, if not check fuse, under the steering wheel following the diagram there.

Secondary voltage test - Connect volt meter between pin 8 (black wire) and pin 9 (Purple & Green wire) you should have battery voltage if not check lock out relay or gear selection switch.

Brake Pedal Test - Connect volt meter between pin 8 (black wire) & pin 5 (green & purple wire). Press the brake pedal, you should get battery voltage.

Steering Wheel Set / Accel Test - Connect volt meter between pin 8 (black wire) & pin 3 (red & white wire). Press the Set / Accel button, you should get battery voltage.

Steering Wheel Res / Decel Test - Connect volt meter between pin 8 (black wire) & pin 4 (blue & white wire). Press the Set / Accel button, you should get battery voltage.

Vacuum Pump Test - Using a jumper wire connect pin 10 (white & yellow wire) to pin 1 (white & blue) this provides power to the pump. Then using a jumper wire connect pin 6 (black & yellow) AND pin 7 (black & red) to pin 8 (black wire). This should energise the pump & solenoid and the bellows (rubber activator on top of the engine) should contract.

Speed Sensor Test - Connect a volt meter between pin 8 (black) and pin 11 (yellow & pink), drive the car around the block, voltage should increase as speed increases.

If any on the above electrical tests fail, you will need to check the associated wires/relays/fuses/connections. If all the tests pass it is likely the cruise control module has failed.
Now, if you have any problem following these instructions, or need any pictures, let me know.
Good Luck

 

My thanks for this post!!! Been trying to decide where to start troubleshooting and this helps a lot!

Since it is -14 degrees out, it may have to wait for spring, or at least above zero.

 

Houmem24.. great info. Thanks

 

Thank you Houmem24 for all of the good info. I think I have narrowed my CC problem down to a faulty pump. I got all of the battery voltages out of the connector you described (I was not able to unplug mine, I just stuck my meter probes into the back of the connector in the wires you described). I could put a hand vacuum pump onto the hose that connects to the Land Rover pump and it would suck the diaphragm and actuate the throttle. But when I hooked up the Land Rover CC pump to my hand vacuum (with a meter on it) it barely moves the needle. Now, if I could figure out how to get the Land Rover CC pump out, I could see if there is anything I could do to correct the low vacuum problem it has, or I could swap it out for another pump.

So now I have two questions:

1. How do I get that pump out

2. If needed, where do I get a replacement pump? (used or new)

Thanks!

 

Well, I believe I found the root of my problem. The pump turns on but doesn't have good suction. This is attributed to the electromagnetic valve inside the pump. It doesn't seal well. If I apply a little pressure (more than the electromagnetic force) it will suck the actuator flat, but I think the little rubber pad that is supposed to seal off the hole is indented (Deformed from the little air nozzle) from so much use that it no longer forms a good enough seal. I ordered a used cc pump from someone off ebay. Hope it works after I put the new pump on.

P.S. I found it very easy to get the pump out by pushing the three little rubber nipple mounts up from underneath with a flat blade screwdriver.

Will post up results after I get the new pump installed.

 

I am glad you are close to solving the problem. Remember, the hoses are tricky too and hard to see the cracks, causing the cruise to fail. I changed mine with fuel hoses and are working just fine.
When you try to put the pump in, it is harder than taking it out. Locate one of the holes, push the tip of the rubber sitting in the hole and then grab the tip of it from under the fender with pliers and pull. the other two will then find their ways in the holes. Remember to test the new pump before installing it. Cheers

 

If it's the same pump as the D2, then there are loads for sale on ebay for about £15 ($20) plus shipping.

 

I found a used pump on ebay from an audi. Hoping that one will work fine too - I think it will - after taking them apart they are pretty simple. One relay connected to two of the prongs that basically allows suction from the pump and the electric motor that connects to the other of the third connector as well as a common terminal with the relay. No chips or anything in there. basically a motor and a relay. Will post back once i get the other pump. i did test the hoses with a hand vacuum pump and when using that, the actuator will pull all the way in to flat (wide open throttle) and held it there for a number of seconds. I did cut some of the ends of the hoses off though as they were starting to split. I could manually hold the relay as the pump was going and it would suck the actuator flat too but only with the assistance of my finger on the relay. I think it was just that little rubber flap relay valve inside the pump that is my problem.

 

Ok, so I bought a cc vacuum pump off ebay from a 1990 Audi Quattro and it is the exact same part number on the bottom plate of the pump as my bad one. I haven't had a chance to try it yet, but for the rest of you - if you need a used replacement pump, look at Audi parts as well. I paid $15 shipped - hope it works - I'll post back with if my system is working again or not.

 

Interesting to know about the compatibility - I assume that they're all Bosch items.