80 cab 1998 cruise not working
 

Hi All

My cab had cruise fitted from new . It hasn't worked since I got it .
I have vcds and checked the car no related faults.
I don't know where to start ?

Any help much appreciated

Vin

Don't know if this is relevant but I have a BMW 740 Sport (E38); this model develops all sorts of faults related to the Light Control Module. This is a box of electrickery that supervises (!) all the gadgetry related to the dashboard instruments, warning lights and steering column controls including the cruise control. It is susceptible to water ingress and when that happens it's a throwaway job. :shake:
Don't know whether the B4 cab has such a module but if so, might be a good place to start.

when you say "no related faults",various other things could stop it working.Faulty ABS is a common one,the stalk itself could well be faulty.

Best way would be to get vcds connected and then you can check the operation of the cruise stalk buttons etc

That vintage probably has a seperate cruise control module (rather than a function of the ECU), and apparently those can develop faults due to dry solder joints on the PCB in the cruise control module.

Most likely though is the stalk (assuming it's the style with the sliding switch on the stalk).
I have a 2001 S8 D2 which has cruise as a function of the ECU, but still uses that old style stalk.
In my case, the clicking ON/OFF function of the switch was intermittant, causing the cruise to cut out or forget the set speed so the resume function didn't work.
I checked in the wiring diagram which two wires go to the ON/OFF switch and shorted them permanently with (horror of horrors) a scotchlock connector.
Cruise is now "ON" all the time, but I drove my previous A4 with the cruise stalk in the ON position all the time for 10 years...

Also check in vcds for the brake and clutch switch operation. I had a broken brake switch in my A4 once. That was a 2 pole switch, so the brake lights still worked ok, but the cruise was permanently disabled as if I had my foot on the brake all the time.

If it does have the separate (Hella) module like the earlier cars, it lives behind the dash above the glove box. They are known to suffer from dry solder joints as mentioned. Made worse by temperature extremes I'm led to believe. Other than the column switch which may have bad or dirty contacts, there are also switches behind the brake pedal (and clutch if manual), to tell the system to disengage if either is pressed so as not to either over-rev the engine or try and counter the act of wanting to stop.

Any of which could stop the system engaging if not 100%.

This earlier system was pneumatic, so it relied on vacuum being created by a small pump in the engine bay, and being maintained in its associated pipes, and bellows. So it can be defeated by leaks in any of that too :)

I have seen this system on early A4s so it may br the case it is the same on yours, i believe it is done purely in the ECU on other models and engine combinations however. HTH.

Mark (VDT) may be able to help if he notices this thread.

:tup:

It will be the same as has already been mentioned Bruce afaik, Vacuum leaks and or electrical.

:tup::tup::tup: