Hello all

i have had a problem with the cruise not working on my 4.0 SE, since i had the car, I have followed the ETM procedure in Rave and it comes back with one problem, which i will tell you about, in a minute. Everything mechanical is fine, vacuum pipes, bellows, pump. Electrical wise, i have replaced the cruise control vent switch and the steering wheel switches. The Cruise ECU and invertor are also working properly. i get a strange voltage reading (about a 100th of what it should be), when i back-probe pin 11 on the cruise control ECU. It says i should get 5 volts with the ignition on and 2.5 volts with the wheels turning. as i said before, i get 0.05 volts with the ignition on and 0.02 with the wheels turning! it says on the Rave ETM, that it is either a problem with the yellow/red wire or the BeCM. I finally checked the continuity of the yellow/red wire yesterday, from the ECU to the BeCM and it was fine. My problem is, is trying to understand what part of the cruise control that operates or inhibits, if that makes sense? Is there another wire that goes into the BeCM, that triggers the voltage? It must use another input from somewhere, but i have looked on the wiring diagrams and i can't see!! I was thinking i might be able to supply power to the Cruise control ECU, from another source, but i need to be careful because the voltage isn't a standard 12 volts. By my way of thinking it is something to do with some kind of wheel speed sensor, to control minimum and maximum speed? it's just a guess, but a point in the right direction, would be a great help.

thanks
Kev

You are sure your multi meter is on the right setting?

Yeah, 100%!!!

Just found this on Rave. Can't see for looking!!

Speed Input
Terminal 11 of the Cruise Control ECU (Z121)
receives the Vehicle Speed output signal from the
BeCM (Z238) through the Y or YR wire. The BeCM
(Z238) receives the vehicle speed signal from the
Anti–lock Brake System ECU (Z108). The signal is a
pulsing voltage and its frequency changes with
vehicle speed.

any advice?

Thanks Kev

I checked the voltage at the BeCM and the ABS plug (yellow/green wire) and i get the same either end. i get 6.5volts with the ignition off and 1.5volts with the ignition on. This is the speed input connection. This relies on the ABS wheel sensors supplying this information. They also supply information for the speedo (which works fine) and also the initial "self-check", up to 5mph, before they extinguish from the instrument cluster (again which does what it should). The more i think about it, the more i think it may be a problem with the BeCM, not "converting" the voltage properly and outputting the signal to the cruise ECU. to be honest, i thought the voltage from the ABS ECU, would be the same as the output voltage, that went to the ECU, but again, the BeCM must "convert" it, or do something to it, to change it to the correct voltage that is required (5volts with the ignition on and 2.5volts with the wheels turning). so i might have finally hit a dead end. I'm certainly not going to start messing about with the BeCM, just to get the cruise working!! What i need to find out, is what the BeCM does to the speed input voltage, to change it to the output voltage. again, any advice would be appreciated.

Thanks Kev

If the output voltage is supposed to be a "pulsing" voltage, then I suspect that you will not be able to check it with a voltmeter as the meter will average the hi's and lo's to give the voltage reading. You need an oscilloscope to look at the waveform

So does that mean, that it could be ok? sorry, but i can check normal voltage, but i have never had to check "pulsing" voltage before!! It said on the ETM it should read 5 volts and 2.5 volts, but it didn't say anything about testing differently. All the other tests come back OK, this was the only one that didn't.

Kev

Little Kev said:

So does that mean, that it could be ok? sorry, but i can check normal voltage, but i have never had to check "pulsing" voltage before!! It said on the ETM it should read 5 volts and 2.5 volts, but it didn't say anything about testing differently. All the other tests come back OK, this was the only one that didn't.

Kev

Click to expand...

I would suspect that they are talking about the logic hi and logic low levels, if so you will not be able to see that on a DVM as the Hi and Low levels may be relatively short duration. I'm not familier with that part of the P38, it's different on the diesel I think so I can't do a comparison check for you, but if it were me I would put an oscilloscope on it which I'm lucky enough to have in my workshop. How you can test it I'm not sure

You need a friendly electronics engineer

Have you looked at the rangerovers.net site? Lots of useful info there covering most problems

Hi Datatek

Thanks for trying to help me out!!! This problem has been bugging me for a while. I have a mate, that i can ask, but i don't know if he has an oscillascope. Maybe someone else, with a petrol 4.0, with working cruise control, could just check pin 11 on the Cruise control ECU and see what reading they get?? I'll have a double check on Rangerovers.net, to see if i missed something.

thanks Kev

Kev

Did you get anywhere on this ? I just got my heap back and about to start to try diagnose same issue on it.

I had the same problem and the same result when trying test 3D in RAVE. Turned out to be dirty contacts in the Cruise Control ECU. An auto ranging digital multimeter struggles with this test. As stated above by Datatek, best to use an oscilloscope.

I have just done the RAVE tests on my Cruise with a multi meter - not sure of some of the readingd (was expecting 13v and got 24v...) but I think I have narrowed the problem down to the inverter thingy (just shows how technical I am) - now where's my hammer......