Cruise Control

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Known as a "Distance System" under the BMW technical manual, the Cruise Control is a simple but practical way of holding the car at a steady speed. Almost standard on US-spec cars but a relative luxury on European vehicles, the cruise control system is a rarely-seen piece of kit, but could transform your E30 into a comfortable bahn-stormer for munching up those motorway miles.

Overview

The cruise control system is essentially a large actuator, meaning a motor which pulls on a cable. This motor/cable assembly bolts onto the inner passenger wing of your car, next to the AFM, and runs its cable directly to the throttle body, in tandem with the existing accelerator cable.

Aside from the actuator, there is also a control lever which fits onto the steering column, next to the indicator lever. For manual cars, there is also a switch to determine when the clutch pedal has been pressed. The whole system is controlled by a separate ECU to monitor vehicle speed and to control the actuator accordingly.

The whole system is linked together with a simple loom that connects to the main vehicle loom by plugging into the accessory socket. An extra cable will run to the dash cluster to read the vehicle speed; this requires an extra plug to be fitted to the dash (known as the Green Plug) which simply slots into the back of all E30 clusters to provide the appropriate connection to the cruise control loom.

Components

CruiseControl01.jpg
CruiseControl02.jpg

Actuator

Black plastic box with a motor mounted inside. Has two cables coming out of it, one with a grommet and a 7 pin electrical connection on the end, the other with a linkage identical to the one that is used for the accelerator pedal cable/throttle arm. Used to keep the throttle in place while cruise is on. Controlled by the ECU.

The actuator is held in place with a bracket. This is the first thing that is somewhat confusing; there are two types of brackets. The one that you will most likely see is the one for factory equipped models. It has three M5 studs coming out of it that match the holes on the servo. It has two holes in it that mount to the studs in the engine compartment above the driver’s side wheel well. If you’re reading this, you probably don’t have cruise already on your car, and probably don’t have the studs either. That’s what the second type of bracket is for. The second type has the same studs as the first, but instead of being mounted to the body above the wheel well, it has holes so it can be mounted to the air filter box mountings.

Loom

Plugs to Image
A Control Lever CruiseControl03.jpg
B Clutch Switch
C Ground
D Actuator Connection
E Auto only relay
F Brake Switch
G Speedo (Green Plug)
H ECU

NOTE: There are two versions of this harness. This is a picture of the harness 12/87 and BEFORE. The other harness is not compatible with cars with this date or before, and this harness is probably not compatible with cars produced after that date.

Control Lever

CruiseControl04.jpg

Turns the cruise on and off, sets and resumes speed. Looks like the windshield washer lever, but has cruise commands on it.

ECU

CruiseControl05.jpg
CruiseControl06.jpg

Big, silver box with 6 sides. One side has a connector on it, this is important. The box controls the servo based on the speedo connection and the actuator lever. This is the brain of the system. It is held in place with a bracket that mounts the unit above the main vehicle ECU

Clutch Switch

CruiseControl07.jpg

Cylindrical push-button switch with a button and some threads on one side, and two male spade connectors on the other. It screws into a custom bracket, which mounts just above the pedal. Used to disengage the cruise control when the clutch pedal is depressed. Above picture is of a brake switch, the clutch switch has a red pushbutton. The clutch switches I have seen have all been stuck in the IN position. This means that the cruise will work all the time, regardless of the clutch position, and will not disengage if the clutch is depressed. I freed mine by spraying WD-40 on it and tapping it gently with a piece of wood.

For cars with automatic transmission, a simple bridging wire plugs into the clutch switch plug on the loom, bypassing the need for a switch.

Ground Wire

Brown wire with M6 lug on one end, and a plug that fits wiring harness plug “C” on the other. Used to provide 0VDC to the system.

Green Plug

Image026.jpg

Plugs into the back of the instrument cluster. Provides a place to plug wiring harness plug “G” into, therefore providing a speedometer pulse to the ECU.

Fitting

Main article: Retrofitting Cruise Control

Since the cruise control is such a desirable accessory for your E30, it's no wonder you would want to fit one yourself. For that reason, we're lucky to host Alex Horvath's original article on installing the cruise. Learn more about retrofitting the cruise control.

Common Problems

Broken Cable Clip

Any plastic gets brittle over time, and the plastic clip that mounts the cruise control cable in place is especially prone to fracturing. When this happens the whole system fails, since the cable has nothing to pull against and therefore can't control the throttle arm properly.

Unless you're really handy with glue, the only workable solution is to remove the actuator and fit a new cable to it. If you're up for it, learn more about replacing the cruise control cable.

Cruise Control Not Working

Disconnect the cruise ECU and the actuator. Use a meter to check that there is a low resistance (not zero) between the green/red wire (9) of the ECU plug and earth. Switch the meter to volts, and check that this wire goes to 12 volts + when you press the brake pedal with the ignition on. Connect a 12 volt 5W or 10W bulb between the purple/white (1) of the ECU plug and brown (23) and check that it lights with the ignition on.