Trouble Shooting

Perform a vehicle road test to verify reports of speed control system malfunction. The road test should include attention to the speedometer. Speedometer operation should be smooth and without flutter at all speeds.

Flutter in the speedometer indicates a problem which might cause surging in the speed control system. The cause of any speedometer problems should be corrected before proceeding. See ANALOG INSTRUMENT PANELS article.

If a road test verifies an inoperative system, and the speedometer operates properly, check for:

• A Diagnostic Trouble Code (DTC). If a DTC exists, see DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS article in ENGINE PERFORMANCE. Perform appropriate test.
• A misadjusted brake (stop) lamp switch. This could also cause an intermittent problem.
• Loose or corroded electrical connections at the servo. Corrosion should be removed from electrical terminals and a light coating of multipurpose grease, or equivalent, applied.
• Leaking vacuum reservoir.
• Loose or leaking vacuum hoses or connections.
• Defective one-way vacuum check valve.
• Secure attachment at both ends of the speed control servo cable.
• Smooth operation of throttle linkage and throttle body air valve.
• Conduct electrical test at PCM.