Range Rover P38 Cruise control fault.

NickNorth said:

2621 is a red unit for petrol V8

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Nooo - I orderd the black one

Just a quick update, cruise control still working normally and on original ECU. Looks like Wd40 & contact cleaner has been thoroughly effective!

Magic

Did you manage to get this fixed ? Inverter pic is on page 19 of the Component Location Views and is item Z249. It is right next to the Cruise ECU.

I am tempted just to pick up both items off a breaking P38.

Mine has been fixed by a simple clean up job on the EcU internals. Has been working perfectly for a or so week now. If you tests lead you to the same issue, then highly likely it is the ECU. Changing it and or the inverter is easy peasy.

Still waiting for the inverter from fleebay - so I will not be able to look at again until Saturday

Put the new inverter on but that did not solve the problem, went through all the test although I did have an issue with the switches on the steering wheel - the test said it should show battery voltage when pressed, but the multi meter took ages to go up in volts and finally seemed to peak at about 7.5v.
I assumed the switched worked though as they did register....

I couldn't do the test for the pump as I had no idea what the wiring diagram ment, so I wipped out the pump and tried to run some voltage through it - the wiring diagram confused me as there are three connectors on the pump and I know one has to be positive and one negative - so I tried running current through each combination but the pump would kick into life so I assume it is dead.

Any help please?

See below, The pump gets 12V on the OU wire and ground on the OR wire. There to check whether it is working you would need to connect both terminals to an alternate live and ground. Finally once the pump is runnig, apply a ground to the remaining wire to close the solenoid switch and start pulling a vacuum.

When cruise control is activated and a cruise speed
is set, the Cruise Control ECU (Z121) applies
voltage through the OU wire and ground through the
OR wire to operate the Cruise Control Vacuum
Pump (M103) motor. The Cruise Control ECU (Z121)
applies ground through the OK wire to close the
normally open solenoid valve in the pump.

Hope this helps.

Thanks RSFH - that is a great explanation - I couldn't get the pump to work on any combination, therefore assume it is FUBAR - have ordered another off fleabay

Wire colour codes are as follows;
OU = Orange/blue
OR = Orange/Red
OK = Orange/pink

RSFH said:

Wire colour codes are as follows;
OU = Orange/blue
OR = Orange/Red
OK = Orange/pink

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If only I wasn't color blind....:doh:

magictiny said:

If only I wasn't color blind....:doh:

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If only I wasn't hung over.......:doh:

Report.....
Following replacing the ecu no problems observed with the cruise control so the ecu was at fault.

Hmmm - pump works - but cruise does not...

So far, replaced, tubing, brake switch, pump, bellows, inverter...

Checked dash switch, that is operational

Only two things left.. ECU and switches on steering wheel...

hi can anyone help i have a 2000 P38 2.5 DSE my cruise was woking fine untill my ujay went since then its not worked HELP please:scratching_chin:

cavalcade said:

hi can anyone help i have a 2000 P38 2.5 DSE my cruise was woking fine untill my ujay went since then its not worked HELP please:scratching_chin:

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check for split pipes on the vacume pump

drewster said:

check for split pipes on the vacume pump

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DSE/Diesels don't use a vacuum system.....it is purely electronic using the EDC to modulate the fuel delivery.

Check the Cruise Control Brake Switch (the P38 has 2 brake switchs...on for the lights and one for the Cruise Control....)

Also check the Rotary Coupler under the Steering Wheel, as this has a tendency to fail....