Cruise Control Woes

[madmanmart]

Hi all,

I'm having problems with the cruise on my 24V Diesel 80.
I get the five flashes and it won't set.
So I've tried swapping over the actuator from a working truck without success. Next I swapped over the cruise ECU and that didn't work either.....
So I jumped the pins on the diagnosis port and the cruise light flashed 12, I have know idea what that means.
Can anyone help me from here?

Mart

 

[Julian T]

Mine did that when I first bought her, repeated use cured the fault, strange as it sounds.

 

[Chris]

Not got a brake light out have you by any chance?

 

[madmanmart]

No but I have a tow bar socket that's not working properly?

 

[Chris]

Ahh, I'd perhaps sort that first. The CC uses resistance through the brake light circuit - so that when you brake, it cuts out. If it detects brakes then it won't set. Also if there is insufficient resistance in the circuit to begin with it won't set. I put LED brake lights in and it wouldn't work. If your tow socket is faulty it might be creating false conditions.

 

[frank rabbets]

Make sure the three little electrical contacts on the gearbox sender are completely clean and tight. Mine looked OK but cleaning the contacts cured it but just putting in a new sender did not.

 

[madmanmart]

Cheers guys, fixing the trailer socket is on my list of things to sort out so I'll start with that.

Three contacts on the gearbox will be be the next port of call.

 

[Pumpy]

Mines not worked since I got it. Does the CC work when a trailer is plugged in?

 

[madmanmart]

Well I completely disconnected the trailer socket and the vss plug seems clean, no difference.....

Any ideas?

 

[frank rabbets]

You've double checked those 3 contacts ? Also there are micro switches on both the clutch and brake pedal. They should obviously be checked.

 

[madmanmart]

I've fixed it!

After trawling through the internet last night I checked the Brake pedal switch,

Swapped out and it works!

 

[Towpack]

Glad you got it sorted. By coincidence I've just got back from Hols in the LC and the CC played up for the first time in the 11 years I've had it. The CC light was on but it just wouldn't set. Played around with it and it cleared after stopping and restarting the engine and been fine since so not really sure what happened there. On the brake light bulb theory I've tried the CC with both bulbs removed and it still works so go figure?

 

[frank rabbets]

The brake light bulbs do not affect cruise control. The brake pedal itself has a switch on it.

 

[Towpack]

I was just relating to what Chris said in post 5 above regarding the CC issues he had when he fitted LED bulbs. AFAIK the CC ecu just looks for an input from the brake or clutch pedal switches, either of which will cancel the CC.

 

[Chris]

Sorry Frank, the brake light bulbs absolutely DO affect cruise. I know because I swapped my bulbs for low resistance LEDs and it went haywire. Swapped em back and it was fixed. Now does a blown bulb affect the cruise? I don't know. Never had that. But if there isn't enough resistance in the system then it does screw it up. Put ballasts in there and all is well. Glad he's sorted it. I figured it was brake related somehow.

 

[frank rabbets]

Well I can't prove a negative Chris but if I look at RME 315 BE 34 the troubleshooting chart lists 10 items that might cause trouble but the brake light circuit is not one of them.

Interestingly when I had my cruise control light flashing due to a fault I did not realise it was talking to me. It does a blink code. That would have told me I had faulty signal from speed sender.

There's no code for brake light circuit.

 

[Chris]

Didn't know it did that Frank. Mine's never blinked. It's either on or off. Interesting. Mine was a nightmare. I swapped the ECU, messed about with the speed sensor and all of that gubbins, then for some reason and I can't recall why, I retraced my steps put the old filaments back in and been running ever since. When my speed sender started to go, on both truck almost simultaneously, my rev counter would go nuts and ping around the dial all over the place then eventually it never got up again. My CC used to cancel for what I though was no reson, then I saw the needle 'blip' just when it cancelled. New unit on and been good as gold since.

 

[frank rabbets]

Yes Chris mine was defo blinking. I thought it was just a loose connection, not being used to blink codes. When I stopped and then went on another journey it would start blinking again. I followed your thread and bought a new speed sender but on seeing those 3 little contacts decided to clean them which cured it. In the WSM there is a blink code for no impulse received from sender which is what I must have been getting. The faulty sender contacts did not cause other problems.