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Home >> Mazda >> 2003 >> MPV ES >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0118: Engine Coolant Temperature Sensor - High Input >> Diagnostic Procedures
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Diagnostic Procedures

  1. Record freeze frame data. Check for service bulletins and on-line information. Repair as necessary. After repair, go to next step.
  2. Verify Current Input Signal Status - Is Concern Intermittent Or Constant -  Connect 104-pin Breakout Box (49-UN01-130) between PCM and PCM harness connector. See Figure. Turn ignition on, engine off. Measure voltage at breakout box terminal No. 38. If voltage reading is more than 4.57 volts, go to next step. If voltage reading is not as specified, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article.
  3. Inspect Poor Connection Of ECT Sensor Connector -  Turn ignition off. Disconnect ECT sensor harness connector, located above starter. Check for damaged, loose or corroded terminals. If problem is present, repair as necessary. After repair, go to step  9. If problem is not present, go to next step.
  4. Classify ECT Sensor Or Harness Malfunction -  Connect a fused jumper wire between ECT harness connector terminals "A" (Light Green/Red wire) and "B" (Orange wire). See appropriate wiring diagram under ENGINE PERFORMANCE in WIRING DIAGRAMS. Measure voltage at breakout box terminal No. 38. If voltage reading is about zero volts, replace ECT sensor. After repair, go to step  9. If voltage reading is not as specified, go to next step.
  5. Inspect ECT Sensor Signal Circuit For Short To Power -  Turn ignition on, engine off. Check voltage between ground and ECT sensor harness connector terminal "A" (Light Green/Red wire). If battery voltage is not present, go to next step. If battery voltage is present, repair short to power in circuit between ECT sensor harness connector terminal "A" (Light Green/Red wire) and PCM 104-pin harness connector terminal No. 38 (Red/Blue wire). See Figure. After repair, go to step  9.
  6. Inspect Poor Connection Of PCM Connector -  Turn ignition off. Disconnect PCM 104-pin harness connector. Check for damaged, loose or corroded terminals. If problem is not present, go to next step. If problem is present, repair as necessary. After repair, go to step  9.
  7. Inspect ECT Sensor Signal Circuit For Open -  Disconnect breakout box from PCM only. Check continuity in wire between ECT sensor harness connector terminal "A" (Light Green/Red wire) and breakout box terminal No. 38. If continuity is present, go to next step. If continuity is not present, repair open in wire between ECT sensor harness connector terminal "A" (Light Green/Red wire) and PCM 104-harness connector terminal No. 38 (Red/Blue wire). After repair, go to step  9.
  8. Inspect ECT Sensor Ground Circuit For Open -  Check continuity in wire between ECT sensor harness connector terminal "B" (Orange wire) and breakout box terminal No. 91. If continuity is present, go to next step. If continuity is not present, repair open circuit between ECT sensor harness connector terminal "B" (Orange wire) and PCM 104-pin harness connector terminal No. 91 (Brown/Yellow wire). See Figure. After repair, go to next step.
  9. Verify Trouble Shooting Of DTC P0118 Completed -  Reconnect all components. Using scan tool, clear DTC. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Turn ignition on, engine off. Recheck DTCs. If DTC P0118 is present, replace PCM. After repair, go to next step. If DTC P0118 is not present, go to next step.
  10. 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, go to applicable test and repair.
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