Cruise Control

[prj]

Well with the signal, there is always a question what fails.
There are multiple circuits on the VSS line and it's just a question of what fails exactly and at which point inside the speedo.

If the rear diff lock still works, then the VSS should definitely be alright.
So the cruise control not working is probably something else. Usual suspects are cold solder joints in the cruise control unit.

[A80Avant]

Yes. Visually checked those in both ecu that I have and they seem pristine

[johne]

If the dash is showing and counting kms as normal, is that a good enough indication that it works?

Also the same cable gets the signal for the rear lock different to turn off after 25km/h. If that still works then can I assume that the signal is still ok?

Yes and yes.

The speed sensor in the gearbox feeds a chip/IC in the instrument cluster that outputs the drive for the speedo, the odometer and produces the VSS signal. This VSS output signal is shared by everything so if the diff lock cuts off, then the VSS to it works.

John

[A80Avant]

That's good. So at least in my case it may still be the cruise control alone causing the problem.

[A80Avant]

Recently after changing a few more items on the cruise control I noticed that it would only work if I kept my finger pressed on the set button continuesly.

So I managed to get a secondhand stalk to replace and see if I can get mine cleaned.

[Joop]

cc fault

My cruise control doesn't works for a while.
I made a quick check with vcds.
The following items looks work:
-break pedal
-clutch pedal
-switching on the cc

The fault is the gas pedal.When i press no bits are changing.
What can be the solution?

[Nuvo]

Ventilation valves at the foot pedals need adjustment maybe?

[Joop]

Ventilation valves at the foot pedals need adjustment maybe?

First i would check the ECU pins:

1. Yellow = ECU plug pin 30
2. Blue = ECU plug pin 45
3. Green = ECU plug pin 48
4. White = ECU plug pin 24
5. Red = Ignition supply (+12v 15amp fused)
6. Black = ECU plug pin 24

Which one gets the acceleration?

[Nuvo]

Pin 8 of the control unit for cruise control is wired to G21 (speedo) via a white/blue wire.

See here for schematic.

[Val]

The fault is the gas pedal.When i press no bits are changing.
What can be the solution?

What car? Old dinosaurs doesn't talk to vcds. Anyway, gas pedal doesn't have only on/off states, so there aren't bits like that.

[veneto rs2]

Quote on Val here.

Gas pedal has nothing to do with the system.
No info of the gas pedal postionit's sent to the cruise ecu.
That's the reason why you have the switches/controls on clutch and brake.
In fact if you put on neutral without pushing the clutch or brake you'll rev the shaite out of your motor...
As stated on the manual on the cruise/tempomat instructions

[Joop]

What car? Old dinosaurs doesn't talk to vcds. Anyway, gas pedal doesn't have only on/off states, so there aren't bits like that.

Sorry i haven't told that the car is A6-C4.It is communicate with VCDS well

[A80Avant]

I wanted to add something I realised after years of intermittently working cruise control system.

After a fair few pumps and a couple of ECUs I traced the problem of failure to the 2 pedal switches.

Their operation is very simple by being able to permanently block the vaccum escaping when the brake or clutch pedal is not pressed. When you deconstruct the switch there is a small o-ring that is meant to secure the vaccumm from escaping when the pedals are not touched.

With time, it degrades and as you blow through the switch you can sense air escaping. My simple fix was to attach a small part of electric tape around the plastic that fits through the o-ring and make it a tight seal.

My cruise control is now working flawlessly and keeps the speed steady without issues.

so before you end up chasing parts, check the pedal switches to see if they are losing vaccumm first.

[macspring]

Thanks for sharing, mine doesn't work at all either, does anyone have the part numbers for the two 'pedal' switches ?

Thanks.

[A80Avant]

The part number is

811 907 343 B. Same for both pedals.

However do take them apart and try what I did. You may end up with a good result