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Home >> Dodge and Ram >> 2002 >> Durango Base, 5.9 Z, 4WD, Part Time >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics - NGC >> Diagnostic Tests >> DTC P0594: Speed Control Servo Power Circuit >> Testing

DTC P0594: Speed Control Servo Power Circuit: Testing

  1. Disconnect the S/C Servo harness connector. Turn the ignition on, with the engine off. Using a 12-volt test light connected to ground, probe the S/C Brake Switch Output circuit in the Servo Harness connector. PRESS and HOLD the Speed Control Switch in the ON position. Does the test light illuminate brightly? If yes, see INTERMITTENT FAILURES  under ON-BOARD DIAGNOSTICS. If no, go to next step.
    2. 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. Install Miller Special Tool (8815) to perform diagnosis.
  2. Turn the ignition off. Reconnect the S/C Servo harness connector. Disconnect the PCM harness connectors. Disconnect the Brakelight Switch harness connector. Measure the resistance of the S/C Supply circuit from the Brakelight Switch harness connector to the appropriate terminal of the Miller Special Tool. Is the resistance less than 5.0 ohms? If yes, go to next step. If no, repair the open/high resistance in the S/C Supply circuit between the PCM and Brakelight Switch.
  3. Measure the resistance between ground and the S/C Supply circuit in the Brakelight Switch harness connector. Is the resistance more than 100 ohms? If yes, go to next step. If no, repair the short to ground in the S/C Supply circuit.
  4. Disconnect the S/C Servo harness connector. Measure the resistance between ground and the S/C Brake Switch Output circuit at the Speed Control Servo harness connector. Is the resistance less than 100 ohms? If yes, repair the short to ground in the S/C Brake Switch Output circuit. If no, go to next step.
  5. Measure the resistance of the S/C Brake Switch Output circuit between the Brakelight Switch harness connector and the S/C Servo harness connector. Is the resistance more than 5 ohms? If yes, repair the open/high resistance in the S/C Brake Switch Output circuit. If no, go to next step.
  6. Reconnect the PCM and Speed Control Servo harness connectors. Turn the ignition on, with the engine off. Using a 12-volt test light connected to ground, probe the S/C Supply circuit in the Brakelight Switch harness connector. Hold the S/C Switch in the ON position to get and accurate reading. Does the test light illuminate brightly? If yes, replace the Brakelight Switch. If no, go to next step.
    7. NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push-out. Repair as necessary.
  7. There are no possible causes remaining, replace the PCM.
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