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Joined: Aug 10 2019
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I need to troubleshoot my cruise control. I've never had to go beyond vacuum problems before so I'm following the procedure in RAVE.

I know I'm just being lazy here but I really don't want to go tearing up the inside panels if someone can just say "no dumb a$$ it's over there".
I'm looking for the cruise control ECU. RAVE electrical component location says it's to the right of the steering column on right hand drive vehicles.
Does anybody know if they moved it to the left of the vehicle for NAS models along with the steering column or did they leave it on the right hand side above what would now be the glove box?

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Joined: Mar 22 2016
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There’s a question, having never pulled a left hooker apart I wouldn’t know, but I bet Richard does,,
Ps welcome to our happy forum

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Joined: Jul 03 2018
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On mine here in the states it is to the left of the steering wheel. Drop the knee panel, try not to rip the little duct vent off.... it is held with a bracket kind of below/behind where the small wood trim is. One or two 8mm bolts and it and the red inverter relay should drop out the bottom.

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Thanks for that info BlackSpeed. I'll go after it there tomorrow.
Kinda funny thing that crotch vent, my other 99my has it but this one doesn't. Glove boxes are a little different also.
LR is kind of famous for that I think when nearing a change in the production line. Things tend to slip in early.

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No Chris, I'm afraid I didn't know. The only left hooker I work on is Mymysteri's diesel in France and it started life as a base model, has had the interior from a more upmarket one fitted but still doesn't have cruise control. Makes sense where it is though, complete mirror image to the RHD.

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Joined: Mar 22 2016
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Gilbertd wrote:

No Chris, I'm afraid I didn't know. The only left hooker I work on is Mymysteri's diesel in France and it started life as a base model, has had the interior from a more upmarket one fitted but still doesn't have cruise control. Makes sense where it is though, complete mirror image to the RHD.

Knew you’d worked on left hooker, I didn’t want to take for granted that they mirrored it, it is a p38 after all, lol

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Well that was kind of my point. Sometimes, in my experience anyway, RAVE fails to mention things because they assume you know and sometimes it's because that isn't the case. So you just have to spend an afternoon looking or ask someone.

Thanks, with your help. It's been located.

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Joined: Jan 16 2017
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Thats not just a Land Rover habbit, I spent several hours looking for a fusebox "behind the glovebox" on a Renault that was actually on the other side of the car behind the handbrake control, Again this is an example of the steering wheel being on the opposite side of the car to where the manual refers to it being.

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Okay......So I know this is a pretty old post but I thought it better to continue it rather that start a new one or steal someone else's.

Among other things I have started working more deeply with the cruise control. Following the troubleshooting flowchart in rave I have tested and retested the circuits to and from the cruise control converter/inverter and ecu.
Everything works well and consistently. The issue I'm having is reading the road speed input on the cruise ECU C243 pin 11 or at the BeCM C255 pin 20.

C255 pin 20 is the road speed output to the Cruise Control ECU, C255 pin 10 is the road speed output to the ATC ECU. The test says 5 VDC at standstill and approx. 2.5 VDC when turning one road wheel by hand. I get 0.042 mV at rest and a very unstable 0.046 to 0.049 at speed. Now not assuming anything about the BeCM I also checked the road speed to the ATC ECU and got 0.48 VDC

Has anyone else ever measured these outputs with a multimeter and if so what readings did you get?
I have an old scope I think I will drag out in the next couple of days and see what I can discover. The only info I can find about it is that it is a "pulsed waveform". Not much to go on in the grand scheme of things.

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Joined: Sep 02 2016
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Not sure but I would assume (!) that the 'pulsed waveform' reference relates to the standard ABS 'sensors/'reluctance' teeth on the hubs combo (?)
I have turned wheels by hand like that myself and the (AC) output from the sensors depends on the speed of the wheel - after all the ABS sensor is just a coil... with chunks of metal going by (the teeth) and this is effectively a waveform generator (?).....
Again , RAVE is not exactly The Bible !

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It isn't the signal directly from the sensors, it's a stream of pulses generated by the ABS ECU at a rate of 8000 pulses per mile. The same pulses drive the speedo and feeds the engine ECU (although quite why the engine ECU needs to know how fast you are going, I've no idea) and are a 12V PWM signal.

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Joined: Sep 02 2016
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That makes sense Richard - the ABS ECU effectively modulates the ABS sensor pulses....

Engine ECUs usually need vehicle speed info as part of their 'MAP' computations, along with RPM, Airflow etc data..
and in some cases (not sure for the P38...) provide inputs to the Gearbox (ECU) to to regulate gear changes too

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Thanks for all the info guys. I know about the AC signal from the wheel sensors feeding into the ABS. Wasn't too sure where the conversion to the pulse waveform was being done, ABS ECU or BeCM but I figured it had to be a DC PWM from what I have been able to gather.

I haven't been able to figure out if the road speed signals to the cruise and the ATC are on a separate buss or just different pins on the same buss. If the same buss I'd almost think the transmission would be having issues of some sort as well. But there could be other components in the circuit to consider. The signal to the GEMS ECU I believe is carried across the data buss.

I dusted off the old Fluke 93 scopemeter and plan to do some measuring when I can make a 12 volt power adaptor for it. I've also bought an old function generator that can output a pulsed waveform and I will try to set a spare cruise ecu up on the bench for testing.

I may also be trying my hand at casting Delrin or Acetal gears to replace the third compound spur gear that fails in the Valeo servo motors. Wish me luck.

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Joined: Sep 02 2016
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Sounds like you know what you are doing Geryhound5 so you probably also know there is an (gearbox) output shaft and (more traditional) road speed indicator in the mix (somewhere) too..... but what are your Cruise Conttrol symptoms ?

As you have surmised with these kinds of signal problems actually driving around with a portable 'scope is much better than 'turning wheels by hand' anyway. I have used (fairly cheap) laptop-based USB 'scopes with (reasonable) success in that regard.

Yes good luck with your casting indeed: Tricky !

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Long story short this P38 has been a pit of despair ever since I bought it and had it shipped 860 miles from out of state. I refuse to give up on it because it's a rather rare Callaway edition. Only 220 made at the end of the GEMS production run.
It was taken very good care of during the first 12 to 15 years of its life by Land Rover dealers but the remaining years receipts are from a shop that I wouldn't let work on a lawn mower.

Among other things the cruise control has never worked since I've owned it. Checked all the common things first, vacuum lines, brake switches and valves, diaphragm, steering wheel switches etc. etc.
Started running through the rave troubleshooting flowchart and the only thing I don't seem to have is the road speed signal. Everything checks out fine. I even replaced the converter/inverter and ecu with used ones just to see if it made any différance.

So I would really like to do my best to isolate the problem to the BeCU or not before I pull it out and send it back to the UK. Turner or Call Rova maybe and probably have the Rangie down all winter. It will be too cold to reinstall it and I don't have room in my garage for another Rover.

Hows that for a short story. Chapter II next week.

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You've got 3 road speed outputs from the BeCM to various things but it should be the same signal on them all. Road speed to the speedo comes from pin 16 (Yellow wire) on C256 (16 pin, white connector), road speed to the HEVAC is from pin 10 (also Yellow) on C255 (20 way white connector and to the Cruise Control ECU from pin 20 (again Yellow) on C255. These are all 0V to Vbatt square waves at 8000 pulses per mile and, according to the BeCM SID, you should see roughly 2.5V DC wrt ground (when moving) if tested with a standard multimeter. Obviously if using a scope, you will see a 12V square wave increasing in frequency with speed. The Road Speed signal from the ABS ECU goes to pin 11 (Yellow/Green wire this time) on C114 (20 pin green connector). Use the one going to the speedo to test first as you know that one is working and you can compare that with what you see on the others.

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Joined: Sep 12 2018
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Greyhound ... I was trying to convince the CC on my GEMS for a long time, too.
Built an adaptor for the later style CC ECU AMR5700 from the THOR models (P38 or Discovery). Not alteration at the cars wiring loom required, just a pigtail from a donor car and an old ECU from the GEMS. I works perfectly since then. Give it a try, seems faster than searching for hours a phantom. Parts are easily available in the digitalbay.
Good luck.

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Joined: Aug 10 2019
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Yes KCR, I've seen that mod/upgrade and the dongle for sale to do plug and play. It's a fine idea and I will have no problem doing it, it's just that sometimes I can't quite something until I feel I have all the facts and answers I can get.

Richard thanks for the updates and confirmations. What you suggested is essentially the path I am going to take. I'm waiting for an inexpensive AC adaptor for the Scopemeter to arrive, so I can cut the cord with the correct, rather interesting pin connector on it and solder it onto a cigar lighter plug for 12 volt operation. I don't have enough extension cord to reach much more than about a 1/4 mile of so. :-)

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Joined: Sep 13 2016
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Is this the "silver can" style ECU, or the later black one?

If its the silver can, its very likely dead. I chased around trying to fix mine, following all the steps in the RAVE etc. In the end the fix was to replace it with the later black plastic cased unit instead and its been flawless ever since.

Oddly enough, about 10 years back i had exactly the same issue with exactly the same cruise control unit in an old Audi. Chased around for months trying to find a good silver unit, and eventually did find one after going thru about 3 or 4 from ebay. You definitely get to that point thinking "it cant be the ECU, i've tried three!"

Given the Autobox output shows the same voltage as the Cruise, you can conclude that either a) they're both dead, or b) they're both working. Given the autobox isnt complaining about missing road speed, i would personally be suspecting that B is the case, and your meter for whatever reason is giving a weird reading.

Given my previous experience with these Hella units, once i'd gone thru the rave instructions and found nothing obvious, i just went directly to replacing it.