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Home >> Mazda >> 2003 >> MX-5 Miata Base, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0118: Engine Coolant Temperature Sensor Circuit High Input >> Diagnostic Procedure

Diagnostic Procedure

  1. Verify Related Repair Information Availability -  Turn ignition off. Connect scan tool to DLC-2. See Figure. 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 ECT Sensor Connector For Poor Connection -  Turn ignition off. Disconnect ECT sensor 3-pin harness connector. See Figure. Check ECTsensor for poor connection 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.
  3. Determine If ECT Sensor Malfunction Or Harness Malfunction -  Measure resistance between ECT sensor 3-pin connector terminals "A" and "B". Resistance reading should be 2270-2740 ohms at 68°F (20°C). If resistance reading is as specified, go to next step. If resistance reading is not as specified, replace ECT sensor. After repair, go to step  8.
  4. Inspect ECT Sensor Signal Circuit For Short To Power -  Measure voltage between ground and ECT sensor 3-pin harness connector terminal "A" (Red/Blue wire). If battery voltage is not present, go to next step. If battery voltage is present, repair short circuit to power in Red/Blue wire between ECT sensor 3-pin harness connector terminal "A" and PCM 31-pin harness connector terminal "4P". See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. After repair, go to step  8.
  5. Inspect PCM Connector For Poor Connection -  Disconnect PCM 31-pin harness connector. See Figure. Check PCM31-pin harness connector for poor connection at terminals "4P" and "4O" due to damaged, pulled-out pins, corrosion, etc. Also check connector terminals for tightness using feeler tool. If connector terminals are okay, go to next step. If connector terminals are found faulty, repair or replace as necessary. After repair, go to step  8.
  6. Inspect ECT Sensor Signal Circuit For Open Circuit -  Check for continuity between ECT sensor 3-pin harness connector terminal "A" and PCM 31-pin harness connector terminal "4P" (Red/Blue wire). If continuity is present, go to next step. If continuity is not present, repair open circuit inRed/Blue wire between ECT sensor 3-pin harness connector terminal "A" and PCM 31-pin harness connector terminal "4P". After repair, go to step  8.
  7. Inspect ECT Sensor GND Circuit For Open Circuit -  Check for continuity between ECT sensor 3-pin harness connector terminal "B" and PCM 31-pin harness connector terminal "4O" (Black/Red wire). If continuity is present, go to next step. If continuity is not present, repair open circuit inBlack/Red wire between ECT sensor 3-pin harness connector terminal "B" and PCM 31-pin harness connector terminal "4O". After repair, go to next step.
  8. Verify Troubleshooting Of DTC P0118 Completed -  Return vehicle to original condition. Using scan tool, clear DTCs from PCM memory. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Start engine and let idle until normal operating temperature is reached. Monitor for pending DTCs. If same DTC is not present, go to next step. If same DTC P0118 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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