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DTC P0703: Brake Switch Sense Circuit: Testing

NOTE: Ensure brake switch is adjusted properly before continuing.
  1. Turn the ignition on. With the DRBIII(R), read DTCs. Is the Good Trip counter displayed and equal to zero? If yes, go to next step. If no, go to step  9 .
  2. Turn the ignition off. Disconnect the brakelight switch harness connector. Using a 12-volt test light connected to ground, check the fused B+ circuit in the brakelight switch harness connector. Does the test light illuminate brightly? If yes, go to next step. If no repair fused B+ circuit as necessary.
  3. Disconnect the brakelight switch harness connector. Disconnect the PCM harness connectors. Remove the Auto shutdown (ASD) relay from the Power Distribution center (PDC). Using a jumper wire, jumper between the fused B+ circuit and ASD relay output circuit in the PDC. Turn the ignition on. Measure the voltage on the brake switch sense circuit in the brakelight switch harness connector. Is the voltage more than one volt? If yes, repair the brake switch sense circuit shorted to voltage. If no, go to next step.
  4. Turn the ignition off. Measure the resistance between ground and the brake switch sense circuit in the brakelight switch harness connector. Is the resistance less than 5.0 ohms? If yes, repair the brake switch sense circuit shorted to ground. If no, go to next step.
  5. Measure the resistance of the brake switch sense circuit between the brakelight switch harness connector and the PCM harness connector. Is the resistance less than 5.0 ohms? If yes, go to next step. If no, repair the brake switch sense circuit for an open.
  6. Reconnect the PCM harness connector. Measure the resistance between ground and the ground circuit in the brakelight switch harness connector. Is the resistance less than 5.0 ohms? If yes, go to next step. If no, repair the ground circuit for an open.
  7. Measure the resistance between the ground circuit and the brake switch sense circuit in the brakelight switch (component side). Apply and release the brake pedal while monitoring the ohmmeter. Does the resistance change from less than 5.0 ohms to open circuit? If yes, go to next step. If no, replace the brakelight switch.
  8. There are no possible causes remaining, replace PCM.
    9. 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.
  9. Conditions that set DTC are not present at this time. The following list may help in identifying the intermittent condition:
    • With the engine running at normal operating temperature, monitor the DRBIII(R) 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(R) Freeze Frame information to identify under what conditions the DTC set.
    • Refer to any Technical Service Bulletin (TSB) that may apply.
    • Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or partially broken wires.
    • Visually inspect the related wiring 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.

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