Cruise Control Doesn't Work
By pdx 528e, Tue Jan 31, 2006
Original thread: Cruise control doesn't work
Factory diagrams for the same system are on Electrical:
Problem: My cruise control does not work.
Possible causes: Bad brake-light connection, defective clutch and brake pedal switches, bad connection to the instrument cluster, defective cruise control brain, or defective cruise control servo. In some cases the control stalk is loose and it is hard to initiate cruise. Automatics are slightly more complicated — cruise takes an input from the transmission range display so it will not function in neutral.
Check the easy things first
- Under the hood, confirm the cruise Bowden cable is fastened to the throttle body next to the throttle cable. If the cable is broken, it is available from BMW; replacement is harder than the rest of this writeup.
- Confirm the brake lights work. Clean the bulb contacts in the tail-light housings (access them by pulling the trunk lining along the tail edge). Cruise is grounded through the brake lights.
- Remove the trim panel below the instrument cluster. Check both pedal switches with a meter:
- Cruise switch should be closed with the pedal up.
- Brake-light switch should be open with the pedal up.
- Replace a bad switch, or adjust the threaded mounting nuts so the pedals make full contact. On a manual, the clutch over-center spring is sometimes needed to keep the pedal against the switch.
Instrument cluster connections
If the pedal switches are good and do not bind, check the cluster.
Cruise needs the large blue plug in the back of the cluster. It is upright, next to a yellow socket of the same type. There are also two smaller connectors at the cluster markings blau and weiss (blue and white) — the connectors are those colors. Install them so the wires point toward the driver's seat, not the front of the car.
Cruise stalk
Check that the stalk does not have a lot of free play. The mounting screw is only reachable with the steering wheel off.
With a test light clamped to a solid ground (the ground behind the steering column):
- Yellow wire has power when off is selected
- Green wire has power when resume is selected
- Blue wire has power when accelerate/set is selected
Brain and servo
If nothing above is wrong, the brain or the servo is defective. The brain is easier and cheaper to replace.
The brain is a medium-size silver box with a blue connector (same shape as the large blue cluster connector). It lives under the dash and steering wheel, in a black holder that also holds the gong and the OBC (if equipped).
If you are at a junkyard anyway, grab both the brain and the servo (engine bay, driver-side fender). A defective brain can make the servo spin and grind whenever the key is in run. After a brain swap the servo may be fine.
If a known-good brain does not fix it, the servo is what is left.
Automatics
Check that the transmission range display is connected and working. Cruise enable needs ground, provided through a blue/brown wire from the neutral light in the transmission range inside the instrument cluster.
Parts
A RealOEM diagram of most cruise components and part numbers.
