Toyota
Dodge Durango
 Service Manual
Speed Control System » Diagnosis and testing
Road test

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. Refer to Group 8E, Instrument Panel and Gauges for speedometer diagnosis.

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

  • A Diagnostic Trouble Code (DTC). If a DTC exists, conduct tests per the Powertrain Diagnostic Procedures service manual.
  • A misadjusted brake (stop) lamp switch. This could also cause an intermittent problem.
  • Loose, damaged or corroded electrical connections at the servo. Corrosion should be removed from electrical terminals and a light coating of Mopar MultiPurpose Grease, or equivalent, applied.
  • Leaking vacuum reservoir.
  • Loose or leaking vacuum hoses or connections.
  • Defective one-way vacuum check valve.
  • Secure attachment of both ends of the speed control servo cable.
  • Smooth operation of throttle linkage and throttle body air valve.
  • Failed speed control servo. Do the servo vacuum test.

CAUTION: When test probing for voltage or continuity at electrical connectors, care must be taken not to damage connector, terminals or seals. If these components are damaged, intermittent or complete system failure may occur.

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