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From digest.v7.n531 Mon Nov 3 15:22:58 1997
From: Jim Cash <>
Date: Mon, 03 Nov 1997 11:26:23 -0500
Subject: Re: 85 325e cruise control

Erik O'Daniel writes:

> One of the problems is broken cruise control.
> Firstly, our Chiltons indicates there is a switch below the steering
> wheel, under the trim, a control module near the glove box, and the
> actuator in the engine compartment.
> Engaging & disengaging the cruise control results in a clacking sound
> from what I assume is the actuator, located above & forwards of the
> driver's-side wheel. (Black tube goes from this item to the throttle
> linkage - cable inside tube. This item does not move when accelerator
> pressed. Should be the cruise control...)
> Clacking does not appear to do anything at the throttle. Moving the
> cruise lever up and down doesn't move anything either. However,
> the only testing I could do with the vehicle in the driveway was
> accelerate slightly and try to engage the cruise. No go. Haven't
> had any luck while driving the vehicle either.


My experience is with a 528e, but the cruise is essentially the same.

The components you describe are correct. Following is a functional description.

The switch on the steering column is all electric, and is connected directly to the "Cruise Control module".

The Module, in turn, is connected electrically to the "Actuator" in the engine compartment.

And, you are correct, the actuator is connected to the throttle with a mechanical cable. This allows the actuator to control the throttle just the same as you would with the accelerator. There should be 2 cables on the throttle arm ( 3 if there is one going down to the automatic transmission )
Make sure both these cables are firmley connected in their little plastic holders. These sometime break (it always interresting when the one for the accelerator breaks just when you go to pass someone - ask me how I know)

The cruise system will not function unless you are going over a certain speed (about 20 MPH). Therefore you can not test this in the driveway (at least not normal city driveways)

When the cruise is activated the control module operates a "clutch" in the actuator. The actuator then has control of it's cable to the throttle.

The fact that you hear a "clacking" could mean that there is a problem with the actuator. It can be taken apart and inspected, but be careful there are springs inside, and the cable must be wound in a specific direction.
But the Control module does not operate the clutch in the actuator until the cruise actually comes into play - so this shoudl not be happening in your driveway.

Need to know exactly where that "clacking" sound is coming from.

Other things that can cause the cruise to not work are:

It must receive information about the speed of the car at all times. It gets this from a lead plugged into the back of the instrument cluster. Assuming the speedometer is working, if the connector for this lead of off, or loose, the cruise will not work. (might be a single blue connector).

The cruise must also get a ground on the lead that goes to the brake light switch. As long as the brakes are not on, it gets the ground "through" the brake light bulbs. (This is how the cruise cuts off when you hit the brakes - the battery to the brake lights cancels the ground to the cruise) If you have any poor connections in the circuit to the brake lights, including the bulbs and ground connections at the car frame, then the cruise may not function.

Of course there are the other obvious items:

  • all electrical connections in place
  • fuse good (try replacing just in case).
  • switch functional - need to test electrically.

BUT - first you should investigate the source, and timing, of that noise.

  • exactly where does it come from?
  • what exactly are you doing when it occurs - operating which switch. Does your car have a separate switch to turn on the cruise, or just the controls on the stalk.

Hope this helps.

If you need more infor pleae write directly.


Jim Cash
London, Ontario, Canada
E39 540ia

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