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 neutral switch one harness connectors. See Fig 1. Measure voltage between ground and neutral switch harness connector terminal "A" (Violet wire). If voltage is not found, go to next step. If voltage is found, repair short circuit to ground (in Violet wire) between neutral switch and PCM. For circuit identification, see MIATA
in WIRING DIAGRAMS article. After repair, go to step 8.
- With neutral switch harness connectors disconnected. Check for poor connection at neutral switch connectors 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 neutral switch harness connectors disconnected. Check continuity between ground and neutral switch harness connector terminal "B" (Black wire). If continuity is found, go to next step. If continuity is not found, repair open circuit (in Black wire) between neutral switch and body ground. After repair, go to step 8.
- Leave neutral switch harness connectors disconnected and 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.
- With neutral switch and PCM harness connectors disconnected, check continuity between neutral switch harness connector terminal "A" and PCM harness connector terminal "4H" (Violet wire). If continuity is found, go to next step. If continuity is not found, repair open circuit (in Violet wire) between neutral switch and PCM. After repair, go to step 8.
- Perform neutral switch inspection. See NEUTRAL SWITCH (M/T)
under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - MIATA, MILLENIA, MPV, PROTEGE, PROTEGE5 & 626 article. If neutral switch is okay, go to next step. If neutral switch is faulty, replace neutral 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. Shift up or down 14 times during test drive. Monitor for DTCs. If same DTC P0850 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.