Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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 SYSTEMΒ .
- Check brake switch adjustment. See BRAKE SWITCHΒ under REMOVAL & INSTALLATION.
- Check for loose or corroded terminals at S/C servo. See COMPONENT LOCATIONSΒ .
- 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 TESTSΒ .
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- β’ You smell fuel, burning insulation, or see smoke.
- β’ Brakes feel soft, pull hard to one side, or make grinding noises.
- β’ The engine overheats, stalls repeatedly, or misfires under load.
- β’ You are missing required tools, torque specs, or safe lifting equipment.
- β’ You are not confident in the next step or safety outcome.
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