Range Rover P38 Cruise control fault.

Hi, I am new to the world of Range Rovers and am looking for some guidance on solving why the cruise control on my 1998 4.6 Autobiography 50, is not working. I have checked and replaced the vacumn hoses and then carried out the fault detection proceedure from RAVE.

On reaching test 3D, there is no voltage coming out of the BECM (C255, pin 20). All else seems to be fine.

Does anyone have any information on the internal circutry of the BECM? Or had a similar experience and found a cost effective solution?

I have the same problem too. the voltage should give 5 v when wheels stationary and 2.5 v when wheel rotating and I get 0.44 volts.

Mine works most of the time except on hot days, all the wiring is ok and connector behind kick panel is clean.

I reckon its a dry joint in the circuit with the output from the BECM which sends a square wave speed signal to the cruise ECU via yellow red cable!
I find if I hard accellerate it wakes the signal up, I ve changed the foot switch, inverter, dash switch, pipes on the pump so now know its the output from the module under the seat.

Thank you for that. bizarrely mines has worked twice in the last two months. on both occasions the weather was blisteringly hot! Maybe something expands enough to remake the connection. will continue looking for a solution in the meantime and post any more findings.

Off out for a meal now, got to keep the rest of the family happy sometimes!

Anyone else have any suggestions its baffling me and wonder if there is an easy way of checking the BECM has the correct output?

My hot weather hypothesis got disproved yesterday. Early morning drive in ambient temperature of 14 degrees C, raining and the cruise control works first try. It continues working throughout the rest of the 40 min journey, resuming etc without problem. On returning to the car to head home a few hours later and it's no show time again for cruise control. Nothing can persuade it back to life.
Every single hardware component must be in working condition and the signal side of things be the problem!

In desperation I removed the cruise control ecu and had a look inside it. No obvious sign of any problems I.e. No burnt smell, signs of leaking capacitors etc. Cleaned the contacts (very carefully) of the board mounted relay and finished off by giving a light dusting with WD40. Reassembled and fitted ecu. Have since driven the car three times ( short journeys only) and the cruise has worked perfectly on each occasion. Is this just coincidence or have I found the culprit? Time will tell, in the meantime a new ecu will be ordered.

Three more seperate trips completed and the cruise control is working perfectly during all of them. So as the only thing different from before, is the ECU having been removed and cleaned, it is fairly safe to assume that the failure of TEST 3D was due to a fault with the cruise control ECU. I am sure the one currently in the car is on borrowed time as I cannot envisage WD40 and contact cleaner being a permanent solution! For reference my ECU is the older type with a silver aluminium cansiter enclosure and part number AR1173. A new one is ordered ansd will kept as a spare unto such a time as the original fails (its an easy job to replace, so don't see the need for preventative intervention i.e. run to failure most cost effective solution).

Hope this helps with your diagnosis Nick.

Interesting you have ordered a ecu I was told that that part is no longer available from LR where did you order one? and how much?

Charles Hurst Land Rover in Belfast, no price as yet and they did indicate that supplies are difficult. time will tell and if not available via that route, I intend to buy one off ebay and get refurbished by an electronics refurbishment company in Dublin. It does not look to be a difficult bit of kit to reverse engineer, fingers crossed.
Bit puzzled at the tests on RAVE not indicating that as the faulty component though,and wasted valuable time chasing the BECM as the culprit!

Hi folks

Same issue with my 97 4.0. Can you tell me what part of RAVE the tests are in ? I printed off a lot of cruise control info but nothing about tests.

In RAVE it is Electrical and trouble Shooting Manuals > Range Rover - 1997 - 6th Edition > Circuit > B5 - Cruise Control

Just read down through it - eventually you will come to the tests.

Can be found on RAVE under RR 1997 - 1998, electrical trouble shooting, circuit, B5 -Cruise Control, page 13 to page 23. It is important to read the ramble before page 13. I printed 13-23 off and than annotated each page as to how the test leads are connected i.e. On the hardware pin, the connector pin or with the connector in position as explained in preamble. Does not take long to run through them once sorted.

Good luck.

Just done my tests - hopefully did them right and it seems to point to the inverter, unfortunatly there seems to be two types...
ERR4277
ERR2621

Now I am not sure which one to buy for my !997 4.6 HSE - if someone knows it will save ma taking the bloomin trim off again..

:doh:Sorry can't help without taking the trim off my RR. Then again shouldn't be that long before I have to anyway!

Thanks guys. I actually found the tests but only got to 1B before the readings didn't match with 11.1V v's 12.6V from battery. I then did 2B anyway just in case the 1.5V difference was ok and it gave me absolutely no reading so not point going past there.

Does anybody have their readings for test 1B to compare to my ones ?

I do have my readings , but not to hand. Can access them in the morning if any use?

tonymccandless said:

Thanks guys. I actually found the tests but only got to 1B before the readings didn't match with 11.1V v's 12.6V from battery. I then did 2B anyway just in case the 1.5V difference was ok and it gave me absolutely no reading so not point going past there.

Does anybody have their readings for test 1B to compare to my ones ?

Click to expand...

you did better than me - I got 24v :doh: But then I can't understand these mutant meters either - I just assumed I was right and the meter was an idiot (I work in IT) and carried onwards until I realised it was the inverter (2 failed tests on that one...)

magictiny said:

Just done my tests - hopefully did them right and it seems to point to the inverter, unfortunatly there seems to be two types...
ERR4277
ERR2621

Now I am not sure which one to buy for my !997 4.6 HSE - if someone knows it will save ma taking the bloomin trim off again..

Click to expand...

Downloaded Microcat and looked through that instead - they do not show the inverter anywere that I could see - doesn't seem to be a search system on it either - so gave up and checked out fleebay again - lo and behold, some kind person was selling the ECU with the inverter together - that wasn't my ECU - I deduce that I need the ERR4277! Didn't even have to open the tool box

Well today I have been to a breakers and got a replacemnet cruise ECU amr1173 and inverter together on the bracket, replaced it and my cruise seems to work ok now. It will be interesting to see how long and if it works at every time, temp etc! will post findings here.

magictiny said:

Downloaded Microcat and looked through that instead - they do not show the inverter anywere that I could see - doesn't seem to be a search system on it either - so gave up and checked out fleebay again - lo and behold, some kind person was selling the ECU with the inverter together - that wasn't my ECU - I deduce that I need the ERR4277! Didn't even have to open the tool box

Click to expand...

2621 is a red unit for petrol V8