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DTC P0703: Brake Switch Sense Circuit: Testing

  1. Turn the ignition on. With the DRBIII®, 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 the Fused B+ circuit.
  3. Turn the ignition off. Disconnect the PCM C2 harness connector. Remove the ASD Relay from the 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 of the Brake Lamp Switch Sense circuit in the Brakelight Switch harness connector. Is the voltage above 1.0 volt? If yes, repair the Brake Switch Sense circuit short to voltage. If no, go to next step.
  4. Turn the ignition off. Measure the resistance of the Brake Lamp Switch Sense circuit in the Brakelight Switch harness connector to ground. Is the resistance below 5.0 ohms? If yes, repair the Brake Lamp Switch Sense circuit shorted to ground. If no, go to next step.
  5. Measure the resistance of the Brake Lamp Switch Sense circuit between the Brakelight Switch harness connector and the PCM C2 harness connector. Is the resistance below 5.0 ohms? If yes, go to next step. If no, repair the Brake Lamp Switch Sense circuit for an open.
  6. Measure the resistance of the Ground circuit in the Brakelight Switch harness connector to ground. Is the resistance below 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 terminal and the Brake Switch Sense terminal in the Brakelight Switch (component side). Apply and release the brake pedal while monitoring the ohmmeter. Does the resistance change from below 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. Program the new PCM. See PROGRAMMING .
    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. 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 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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