help!!! cruise control problem

[tim s]

hi,
my 1995 540i/a cruise control has been acting up. it will randomly not work. when i engage it, it does not accelerate, the gas pedal taps the bottom of my foot. could this be a problem with the actuator or is it an electrical problem such as the switch on the brake pedal.
thanks
tim s.
1995 540i/a
1987 325e

[tim s]

hi,
my 1995 540i/a cruise control has been acting up. it will randomly not work. when i engage it, it does not accelerate, the gas pedal taps the bottom of my foot. could this be a problem with the actuator or is it an electrical problem such as the switch on the brake pedal.
thanks
tim s.
1995 540i/a
1987 325e

[gale]

The brakelight switch down by the pedals is a 2-pole switch. The leg for the brakelights is normally open and will register a fault with the check control when the points become pitted to the point of putting the circuit resistance above a certain amount. The one for the cruise control is normally closed but if those points get resistive, it can keep the cruise from latching in. I don't believe it registers a fault when that leg becomes resistive. Here's more info on changing/cleaning the switch:

http://www.nmia.com/~dgnrg/page_25.htm

Bruno also has more info on his page.

You might also remove & clean the connector for the throttle position switch, it can contribute to cruise control problems. Also, take the cover off the "E-box" and clean the connector on the cruise control module:

http://www.nmia.com/~dgnrg/ebox.jpg

Another culprit sometimes is the speed sensor and/or connector on the back of the diff, but if that's problematic, you'll be having blips in the speedo needle.

In older e28's, the brakelight bulbs could cause the cruise control to go on the fritz if the wrong bulbs are used or if the sockets are corroded. If none of the above suggestions help, then clean or replace the brakelight bulbs, don't use brass ones, get the OE Osram bulbs or another bulb with a nickel base.

I would at least go thru all of the above before succumbing to the $tealer.

gale

[WarrenBrown]

Maybe this doesn't apply to E34 cars, in E30 cars the cruise control is affected by brass base brake light bulbs. It causes a difference in the resistance that the cruise control senses.

Warren
91 318is
95 525iT

[tim s]

hi,
my 1995 540i/a cruise control has been acting up. it will randomly not work. when i engage it, it does not accelerate, the gas pedal taps the bottom of my foot. could this be a problem with the actuator or is it an electrical problem such as the switch on the brake pedal.
thanks
tim s.
1995 540i/a
1987 325e

[David Chen]

The cruise control actuator is "acting up". It's the black box behind the driver side highbeam that's labelled VDO. Open it up and clean out all the accumulated gunk (you'll know what I mean when it's open) using electrical contact cleaner spray. Alternatively, pony up $400 for a new one at the dealer.

Cheers,

David
'95 M540i -- c/c actuator cleaned twice, replaced once.