Cruise Control General Information and Repair

Introduction

Cruise control problems are fairly common in 944s. The most frequent symptoms include failing to engage, failing to maintain speed, and picking up a set amount of speed after engagement (typically 5–10 mph). Most cruise control problems can be resolved without major expense if the work is done by the owner.

The two major components are the cruise control computer, located in the driver's footwell (LHD) above the hood release lever, and the cruise control servo unit, mounted on the firewall in the engine bay just in front of the battery tray.

Many symptoms can be caused by either unit. If the source is unclear, clean the servo first, reinstall, and test before doing further repairs. Use the troubleshooter below to help narrow the cause.

Cruise Control Troubleshooter

Symptom	Possible Cause
Acceleration above preset speed (normally 5–10 mph)	Servo unit
Operates intermittently	Cruise control computer or servo
Fails to engage or operate	Cruise control computer

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Cleaning the Servo Unit

Tools

• Metric socket/wrench set
• Phillips screwdriver
• Small flat-tip screwdriver
• Spray contact cleaner
• Cotton swab

Procedure

1. Disconnect the throttle cable from the servo. The cable is held by a clip; remove the metal retainer from the clip and slide the clip off the ball on the servo operating arm.
2. Disconnect the servo electrical connector.
3. Remove the servo from the vehicle.

Note: Make a sketch of the servo assembly before disassembly. This simplifies reassembly.

4. Remove the operating lever arm from the servo by removing the nut that holds it in place.
5. Using a Phillips screwdriver, carefully remove the cover from the servo. A small spring inside may try to pop out. A small flat-tip screwdriver can help pry the cover off if it is stuck.
6. Inside the servo, locate the circuit board with two conducting strips contacted by a wiper arm. Dirty conducting strips are the most common cause of servo problems.
7. Using spray contact cleaner and a cotton swab, carefully clean the conducting strips. Do not rub aggressively — the strips can be damaged.
8. Check the motion of the wiper arm to confirm it is making good contact with the circuit board.
9. Apply grease to the moving parts inside the servo. Keep grease off the conducting strips and wiper arm.
10. Reassemble the servo, install in the vehicle, and test for proper operation.

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Cruise Control Computer Repairs

Tools

• Small flat-tip screwdriver
• Phillips screwdriver
• Magnifying glass or lens
• Soldering iron with flux-core solder
• Solder removal tool (solder sucker)
• Small wire brush
• Isopropyl alcohol
• Cleaning swabs

Procedure

1. Locate the cruise control computer — the silver box above the hood release lever in the driver's footwell.
2. Disconnect the electrical connector. Remove the mounting screws and remove the unit from the vehicle.
3. Open the cruise control computer by bending back the tabs on the cover using a flat-tip screwdriver.
4. Remove the circuit board from the unit.
5. Using the magnifying glass, inspect all solder joints on the board. Good solder has a bright, shiny appearance. Faulty joints appear dull and may have a ring or halo around the component leg.
6. Repair any poor or questionable solder joints. The circuit board is typically coated with a protective lacquer. Heat the joint, remove the old solder and lacquer using the solder sucker, then clean the area with a small wire brush.
7. Re-solder the joint, ensuring solder flows fully into the joint. Once cooled, clean residual flux with isopropyl alcohol and a swab.
8. Reassemble the cruise control computer.
9. Install the computer and road test.