Speed Control Inoperative

Road test vehicle and monitor Speed Control (S/C) system and speedometer operation. If road test verifies a malfunctioning S/C system and speedometer, diagnose speedometer problem before proceeding. See ANALOG INSTRUMENT PANELS - CONCORDE, INTREPID & 300M article. If road test verifies a malfunctioning S/C system, but speedometer operates properly, perform the following checks:

• Turn ignition off. Connect scan tool. Using scan tool, retrieve DTCs. If DTCs exist, go to SELF-DIAGNOSTIC SYSTEM .
• Check brake switch adjustment. See BRAKE SWITCH  under REMOVAL & INSTALLATION.
• Check for loose or corroded terminals at S/C servo. See COMPONENT LOCATIONS .
• Check for leaking vacuum reservoir.
• Check for loose or leaking vacuum supply lines.
• Check for defective one-way vacuum check valve.
• Check that both ends of servo control cable are attached securely.
• Check that throttle linkage is not damaged or binding.
• Check for damaged, binding or faulty servo.

If system and components appear to be okay and no DTCs are set, perform appropriate test(s) under SYSTEM TESTS .