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DTC P0579: Speed Control Switch #1 Performance: Testing

  1. Turn ignition on, engine not running. With the DRBIII®, monitor each switch function for the Speed Control Switches. Press and release each Speed Control Button (Resume/Accel, Cancel, Decel (Coast), On/Off and Set) Does each switch function change status when pressing and then depressing each switch? If yes, go to next step. If no, go to step  3.
    2. WARNING: When the engine is operating, do not stand in a direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing.
  2. The conditions that set the DTC are not present at this time. The following may help in identifying the intermittent condition. With the engine running at normal operating temperature, monitor the DRBIII® parameters related to the DTC while wiggling the wiring harness. Look for parameter values to change and/or a DTC to set. Review the DRBIII® Freeze Frame information. If possible, try to duplicate the conditions under which the DTC was set. Refer to any Technical Service Bulletins (TSB) that may apply. Visually inspect the related wire harness. Look for any chafed, pierced, pinched, or partially broken wires. Visually inspect the related wire harness connectors. Look for broken, bent, pushed out, or corroded terminals. Were any of the above conditions present? If yes, repair as necessary. If no, test is complete.
  3. Turn the ignition off. Remove the Speed Control Switches from the steering wheel. Measure the resistance across each Speed Control Switch. Monitor the ohmmeter while pressing each function button on each switch. Do the Speed Control Switches have the correct resistance value? See SPEED CONTROL SWITCH RESISTANCE  table. If yes, go to next step. If no, replace the Speed Control Switch that had the incorrect resistance value.
    SPEED CONTROL SWITCH RESISTANCE

    Switch Ohms
    Cancel 900-918
    Decel (Coast) 2910-2970
    On/Off 0
    Resume/Accel 15,400
    Set 6584-6716
  4. Ensure the ignition is off. Disconnect the PCM harness connector. Measure the resistance between the Speed Control Switch Signal circuit and the Sensor Ground circuit at one of the Speed Control Switch harness connectors. Is the resistance below 5.0 ohms? If yes, repair the Speed Control Switch Signal circuit that is shorted to the Sensor Ground circuit. If no, go to next step.
  5. Measure the voltage of the Speed Control Switch Signal circuit at one of the Speed Control Switch harness connectors. Is the voltage above 5.0 volts? If yes, repair the short to voltage in the Speed Control Signal circuit. If no, go to next step.
  6. Measure the resistance between ground and the Speed Control Switch Signal circuit at one of the Speed Control Switch harness connectors. Is the resistance below 100 ohms? If yes, repair the Speed Control Switch Signal circuit that is shorted to ground. If no, go to next step.
    7. CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal-to-pin connection. Use Miller Special Tool (8815) when performing diagnosis at PCM harness connectors.
  7. Measure the resistance of the Speed Control Switch Signal circuit from the Speed Control Switch harness connector to the appropriate terminal of the Miller Special Tool. Measure resistance at both Speed Control Switch harness connectors. Is the resistance below 5.0 ohms for both measurements? If yes, go to next step. If no, repair the open in the Speed Control Switch Signal circuit.
  8. Measure the resistance of the Sensor Ground circuit from the Speed Control Switch harness connector to the appropriate terminal of the Miller Special Tool. Measure resistance at both Speed Control Switch harness connectors. Is the resistance below 5.0 ohms for both measurements? If yes, go to next step. If no, repair the open in the Sensor Ground circuit.
    9. NOTE: Before continuing, check the PCM harness connectors for corrosion, damage or terminal push out. Repair as necessary.
  9. There are no possible causes remaining, replace PCM. Program the new PCM. See PROGRAMMING .
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