Cruise Control – General Information and Repair

Overview

This guide covers the maintenance and repair of the cruise control system on the Porsche 944 (16v engine). The cruise control system helps maintain a consistent speed during long drives, improving comfort and fuel efficiency. Common issues include failure to engage, inconsistent operation, or unintended acceleration after setting the speed. This procedure focuses on cleaning the cruise control servo unit and repairing the cruise control computer, which are the primary components for the 944 models. Most issues can be resolved with basic tools and careful attention to detail, making this a cost-effective DIY repair.

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Cruise Control Troubleshooter

Tools Required

• Metric socket and wrench set (including 10mm / 3/8 inch and 13mm / 1/2 inch sizes)
• Phillips screwdriver
• Small flat-tip screwdriver (3mm / 1/8 inch blade)
• Spray contact cleaner
• Cotton swabs
• Automotive grease
• Magnifying glass or lens
• Soldering iron and flux-core solder
• Solder removal tool (solder sucker)
• Small wire brush
• Isopropyl alcohol

Parts Required

• None (assuming no replacement parts are needed; otherwise, use 944 110 901 00 for servo unit or 944 618 111 00 for cruise control computer if replacement is required)

Step-by-Step Procedure

Step 1: Cleaning the Cruise Control Servo Unit

1. Locate the cruise control servo unit on the firewall in the engine bay, just in front of the battery tray.
2. Disconnect the throttle cable from the servo:- Remove the metal retainer from the clip securing the cable.

   Slide the clip off the ball on the servo’s operating arm.

3. Disconnect the servo’s electrical connector by gently pulling it apart.
4. Remove the servo unit from the vehicle by loosening the mounting bolts using a 10mm (3/8 inch) socket or wrench.
5. Create a sketch or take a photo of the servo assembly for reference during reassembly.
6. Remove the operating lever arm from the servo:- Use a 13mm (1/2 inch) wrench to remove the nut securing the lever arm.
7. Carefully remove the servo cover using a Phillips screwdriver:- Be cautious of a small spring inside that may pop out.

   If the cover is stuck, gently pry it off with a 3mm (1/8 inch) flat-tip screwdriver.

8. Locate the circuit board inside the servo, which has two conducting strips and a wiper arm.
9. Clean the conducting strips on the circuit board:- Use spray contact cleaner and a cotton swab.

   Clean gently to avoid damaging the strips.

10. Check the wiper arm’s motion to ensure it makes good contact with the circuit board.
11. Apply a small amount of automotive grease to the moving parts inside the servo:- Ensure no grease contacts the conducting strips or wiper arm.
12. Reassemble the servo by securing the cover with the Phillips screwdriver.
13. Reinstall the servo unit in the vehicle:- Tighten the mounting bolts to 10 Nm (7.4 ft-lbs) using a 10mm (3/8 inch) socket.
14. Reconnect the throttle cable and electrical connector.
15. Test the cruise control system by driving 5 miles (8 km) to verify proper operation.

Step 2: Repairing the Cruise Control Computer

16. Locate the cruise control computer in the driver’s footwell (left-hand drive), above the hood release lever.
17. Disconnect the electrical connector from the cruise control computer.
18. Remove the computer by unscrewing the mounting screws using a Phillips screwdriver.
19. Open the computer by bending back the cover tabs with a 3mm (1/8 inch) flat-tip screwdriver.
20. Remove the circuit board from the computer housing.
21. Inspect all solder joints on the circuit board using a magnifying glass:- Good solder joints should be bright and shiny.

    Poor joints will appear dull or have a ring around the component leg.

22. Repair any poor solder joints:- Heat the joint with a soldering iron and remove old solder using a solder removal tool.

    Clean the joint area with a small wire brush to remove protective coating.

23. Re-solder the joint with flux-core solder, ensuring the solder flows smoothly into the joint.
24. Clean residual flux from the joint using isopropyl alcohol and a cotton swab.
25. Reassemble the cruise control computer by securing the cover.
26. Reinstall the computer in the vehicle:- Tighten the mounting screws to 8 Nm (5.9 ft-lbs) using a Phillips screwdriver.
27. Reconnect the electrical connector.
28. Road test the vehicle by driving 5 miles (8 km) to confirm the cruise control functions correctly.

Post Procedure Checklist

• Verify the cruise control engages when activated.
• Check that the vehicle maintains the set speed without accelerating 5-10 mph (8-16 km) above the preset speed.
• Ensure the system operates consistently without intermittent failures.
• Inspect the servo unit and computer for secure mounting and proper connections.
• Confirm no warning lights appear on the dashboard related to the cruise control system.

Sources

• Clark’s Garage
• Pelican Parts
• Porsche 944 Workshop Manuals
• Youtube