Diagnostic Procedure
- Turn ignition off. Connect New Generation Star (NGS) tester or equivalent to OBD-II Data Link Connector-2 (DLC-2). See Figure. Turn ignition on. Monitor for FREEZE FRAME DATA and ensure data has been recorded. Check for service bulletins and/or other line of repair information related to this DTC. If repair information is available, perform diagnosis and repair as necessary. After repair, go to step 8. If repair information is not available, go to next step.
- Turn ignition off. Disconnect brake switch 2-pin harness connector. See Fig 1. Turn ignition on. Measure voltage between ground and brake switch harness connector terminal "B" (Green wire). If battery voltage is not found, go to next step. If battery voltage is found, repair short circuit to voltage (in Green wire) between brake switch and PCM. For circuit identification, see MIATA
in WIRING DIAGRAMS article. After repair, go to step 8.
- Turn ignition off. With brake switch harness connector disconnected, check for poor connection at brake switch connector terminals due to damaged, pulled-out pins, corrosion, etc. If connector terminals are okay, go to next step. If connector terminals are found faulty, repair or replace as necessary and go to step 8.
- With brake switch harness connector disconnected, turn ignition on. Measure voltage between ground and brake switch harness connector terminal "A" (White/Green wire). If battery voltage is found, go to next step. If battery voltage is not found, repair open or short circuit (in White/Green wire) between engine compartment main fuse block and brake switch. After repair, go to step 8.
- Turn ignition off. Disconnect PCM 31-pin harness connector terminal. See Fig 1. Check for poor connection at PCM connector terminals due to damaged, pulled-out pins, corrosion, etc. If connector terminals are okay, go to next step. If connector terminals are found faulty, repair or replace as necessary and go to step 8.
- Leave PCM harness connector disconnected and reconnect brake switch harness connector. Turn ignition on. While depressing brake pedal measure voltage between ground and PCM harness connector terminal "4B" (Green wire). If battery voltage is found, go to next step. If no battery voltage is found, repair open or short circuit (in Green wire) between brake switch and PCM. After repair, go to step 8.
- Turn ignition off. perform brake switch inspection. See BRAKE LIGHT SWITCH
under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - MIATA, MILLENIA, MPV, PROTEGE, PROTEGE5 & 626 article. If brake switch is okay, go to next step. If brake switch is faulty, replace brake switch. After repair, go to next step.
- Return vehicle to original condition. Using NGS tester or equivalent, clear DTCs from PCM memory. Start engine and let it idle until it reaches normal operation temperature. Drive vehicle at 18.6 MPH or above. depress brake pedal 10 times or more during test drive. Monitor for DTCs. If same DTC P0703 is present, replace PCM. For PCM removal and installation, see POWERTRAIN CONTROL MODULE
in REMOVAL, OVERHAUL & INSTALLATION article. If any other DTC is present, follow appropriate DTC diagnostic procedure.
Courtesy of MAZDA MOTORS CORP.