Cruise Control Not Working

[StewartIngram]

I've had KV6's since 2007, and always done my own maintenance.
I agree that the brake pedal switch is the most likely cause, everyone seems to mention that. However, on occasions I have suffered a different symptom. On the bulkhead, offside of the engine, you will find the vacuum pump. The hose from the throttle body diaphragm should terminate on this; I have had it loose or dropped off on 2-3 occasions.

[Mike Noc]

Originally Posted by daveo138

Thanks Mike. I did wonder about that. I tested the horn last night and it worked OK.

Is there an easy way to test the rotary coupler other than replacing it?

Well I thought it would take longer to trace and check the cables out than it would to just replace the coupler, so seeing as I had a spare one from a scrapper I tried it and that cured the fault.
Splitting the coupler and inspecting the ribbon cable I found a split that had started to run across it, so if your radio buttons aren't working as well it may well be that the ribbon cable has started to go south.

[Mike Noc]

Originally Posted by StewartIngram

I've had KV6's since 2007, and always done my own maintenance.
I agree that the brake pedal switch is the most likely cause, everyone seems to mention that. However, on occasions I have suffered a different symptom. On the bulkhead, offside of the engine, you will find the vacuum pump. The hose from the throttle body diaphragm should terminate on this; I have had it loose or dropped off on 2-3 occasions.

Dave's car is a diesel Stewart so no vacuum pump (well there is but only for the brakes and EGR). The system is fully electronic drive by wire.

[daveo138]

Originally Posted by Mike Noc

Well I thought it would take longer to trace and check the cables out than it would to just replace the coupler, so seeing as I had a spare one from a scrapper I tried it and that cured the fault.
Splitting the coupler and inspecting the ribbon cable I found a split that had started to run across it, so if your radio buttons aren't working as well it may well be that the ribbon cable has started to go south.

I've had a quick look at the wiring diagram. If I hotwire a momentary switch into the rotary coupler plug, linking the light green/red with the black wire, it should act as the 'set' switch and proves whether everything as far as that point still works, hopefully.

[Mike Noc]

Yep that sounds like a good plan. 👍

[daveo138]

I've just been out experimenting.

I disconnected the plug from the rotary coupler and hot wired a switch across the light green/red and the black wires.



It still doesn't work, so the fault is obviously elsewhere.

I didn't realise when I was checking at Gaydon, but there are actually two fuses for cruise control. I've checked the other one and that is also good.

A couple of things are confusing me. The wiring schematic shows a cruise control ECU for the petrol model and a cruise control relay for diesels. Mine is a diesel. I can find no mention of this relay - R142 - or its location.

The schematic also shows a feed from fuse 4 in the engine bay fuse box to the CC relay.

Last but not least, the schematic for the rotary coupler would appear to have an error. I would expect the common side of the two cruise switches to be connected to ground, along with the horn buttons, but the schematic shows them connected to the wrong side of the horn buttons.



So, does anyone know where the CC relay is located? That might be my next step, along with checking fuse 4 in the engine bay fuse box.

[SD1too]

Originally Posted by daveo138

Mine is a diesel. I can find no mention of this relay - R142 - or its location.

That's because it's not a relay! It's an interface ECU. It is located in the passenger footwell behind the fascia.

Originally Posted by daveo138

Last but not least, the schematic for the rotary coupler would appear to have an error. I would expect the common side of the two cruise switches to be connected to ground, along with the horn buttons, but the schematic shows them connected to the wrong side of the horn buttons.

I agree Dave.

Simon