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Home >> Mazda >> 2003 >> Protege5 Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0850: Neutral Switch Input Circuit Malfunction >> Diagnostic Procedure

Diagnostic Procedure

  1. Verify Related Repair Information Availability -  Turn ignition off. Connect scan tool to DLC-2. Turn ignition on, engine off. Monitor for FREEZE FRAME DATA and ensure data has been recorded. Check service bulletins for repair information related to this DTC. If repair information is not available, go to next step. If repair information is available, perform diagnosis and repair as necessary. After repair, go to step  8.
  2. Inspect Neutral Switch Signal Circuit For Short To Power -  Disconnect PCM 104-pin harness connector and neutral switch 2-pin harness connector. Connect 104-pin Breakout Box (49-UN01-130) to PCM harness connector only. See Figure. Turn ignition on, engine off. Measure voltage between ground and breakout box terminal No. 64. See Figure. If battery voltage is not present, go to next step. If battery voltage is present, repair short circuit to power in Pink/Green wire between PCM 104-pin harness connector terminal No. 64 and neutral switch harness connector terminal "A". See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. After repair, go to step  8.
  3. Inspect Neutral Switch Connector For Poor Connection -  Turn ignition off. Disconnect neutral switch 2-pin harness connector. Check for poor connection due to damaged, pulled-out terminals, corrosion, etc. If no problems are found, go to next step. If any problems are found, repair as necessary. After repair, go to step  8.
  4. Inspect Neutral Switch Signal Circuit For Open Circuit -  Reconnect PCM 104-pin harness connector and neutral switch harness connector. Turn ignition on, engine off. Measure voltage between ground and neutral switch harness connector terminal "A" (Pink/Green wire). If battery voltage is present, go to next step. If battery voltage is not present, repair open circuit in Pink/Green wire between neutral switch harness connector terminal "A" and PCM 104-pin harness connector terminal No. 64. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. After repair, go to step  8.
  5. Inspect PCM Connector For Poor Connection -  Turn ignition off. Disconnect PCM 104-pin harness connector. See Figure. Check for poor connection due to damaged, pulled-out terminals, corrosion, etc. If no problems are found, go to next step. If any problems are found, repair as necessary. After repair, go to step  8.
  6. Inspect Neutral Switch Connector Circuit For Open Circuit -  Disconnect neutral switch 2-pin harness connector. Turn ignition on, engine off. Ensure transaxle is in neutral. Depress clutch pedal and measure voltage between body ground and neutral switch harness connector terminal "A" (Pink/Green wire). If voltage reading is less than one volt, go to next step. If voltage reading is zero, repair open circuit in Pink/Green wire between neutral switch harness connector terminal "A" and PCM 104-pin harness connector terminal No. 64. After repair, go to step  8.
  7. Inspect Neutral Switch Signal Circuit For Open Circuit -  Connect 104-pin Breakout Box (49-UN01-130) to PCM harness connector only. See Figure. Turn ignition on, engine off. Ensure transaxle is in neutral. Measure voltage between ground and breakout box terminal No. 64. If voltage reading is less than one volt, go to next step. If voltage reading is zero, repair open circuit in Pink/Green wire between neutral switch harness connector terminal "A" and PCM 104-pin harness connector terminal No. 64. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. After repair, go to step  8.
  8. Verify Trouble Shooting Of DTC P0850 Completed -  Reconnect all connectors. Turn ignition on, engine off. Using scan tool, clear DTCs. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Start engine and let idle until normal operating temperature is reached. Drive vehicle at 18.6 MPH or more. Shift up or down 14 times during test drive. Monitor for DTCs. If same DTC is not present, go to next step. If same DTC is present, replace PCM. For PCM removal and installation, see POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION article. After repair, go to next step.
  9. Verify After Repair Procedure -  Using scan tool, perform After Repair Procedure. See AFTER REPAIR PROCEDURE . If no other DTCs are present, testing is complete. If any other DTC is present, follow appropriate DTC diagnostic procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
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