DTC P0703: Brake Switch #2 Circuit: Testing

NOTE: Brakelight switch may also be referred to as brake switch, brakelamp switch or stoplamp switch.

NOTE: Ensure the Brakelight switch is adjusted properly before continuing. See appropriate DISC article in BRAKES.

Turn ignition on, engine not running. With the DRBIII®, read DTCs and record the related Freeze Frame data. Is the Good Trip counter displayed and equal to zero? If yes, go to next step. If no, go to step 9.
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, replace related fuse or repair the Fuse B+ circuit as necessary.
Turn the ignition off. Disconnect the PCM harness connectors. 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 Switch Sense circuit in the Brakelight Switch harness connector. Is the voltage above 1.0 volt? If yes, repair the short to voltage in the Brake Switch Sense circuit. If no, go to next step.
Turn the ignition off. Measure the resistance between ground and the Brake Switch Sense circuit in the Brakelight Switch harness connector. Is the resistance below 5.0 ohms? If yes, repair the short to ground in the Brake Switch Sense circuit. If no, go to next step.

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.

Measure the resistance of the Brake Switch Sense circuit from the Brakelight Switch harness connector to the appropriate terminal of the Miller Special Tool. Is the resistance below 5.0 ohms? If yes, go to next step. If no, repair the open in the Brake Switch Sense circuit.
Measure the resistance between ground and the Ground circuit in the Brakelight Switch harness connector. Is the resistance below 5.0 ohms? If yes, go to next step. If no, repair the open in the Ground circuit.
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.
There are no possible causes remaining, replace PCM. Program the new PCM. See PROGRAMMING .

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.

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.