martyuk
Well-Known Member
Mary,
How do you know my 'weekend name'
The cruise lines are a common culprit on all model years of P38 - but also unfortunately on the earlier GEMS models, it is usually the cruise ECU that fails. I know a couple of owners on RR.net have fixed theirs, usually by reflowing the solder joints across the PCB of the cruise ECU, but a couple have also posted up pinouts for swapping the ECU for the later Bosch version, which doesn't seem to suffer the same fate.
The steering wheel switches are usually pretty reliable - the most common reason for them to stop working is if the rotary coupler fails - but then all the switches will stop, along with the horn - and you usually get an Airbag Fault as the drivers air bag loses connection. If you have none of those, then my bet is on the vacuum lines, or the ECU.
Also worth noting it that the power to the vacuum pump goes through the infamous 'kick panel connectors' in the LH footwell. They are known to go green and corrode, so could be another spot worth checking.
I think the reason they probably use a separate pump is so the vacuum can be varied to allow for holding the throttle and being able to move it to adjust the speed aswell. I guess if you could do it with intake vacuum, but having a controllable pump makes it easier for the ECU to control.
Marty