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Home >> Mitsubishi >> 2003 >> Lancer Evolution >> Repair and Diagnosis >> External Pages >> Different car >> Section 5 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P0125: Engine Coolant Temperature Sensor Excessive Time To Closed Loop Fuel Control >> Diagnostic Procedure
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Diagnostic Procedure

WARNING: This page is about a different car, the 2002 Isuzu Trooper. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform ON-BOARD DIAGNOSTIC II SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing OBD-II system check, go to next step.
  2. If any ECT sensor DTCs are set, repair those DTCs first. For diagnostic procedure, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no DTCs are set, go to next step.
  3. Allow engine to cool. Ensure coolant level is full. If coolant level is okay, go to next step. If coolant level is low, go to step  9.
  4. Start engine and let idle. Using scan tool, observe ENG COOL TEMP parameter. If display increases to more than 70°F (21°C) within 2 minutes, check for an intermittent problem. See DIAGNOSTIC AIDS . If display is not as specified, go to next step.
  5. Check thermostat for proper operation. If thermostat is okay, go to next step. If thermostat does not operate properly, go to step  9.
  6. Using a thermometer, check temperature of coolant in radiator. Compare reading with display on scan tool. If readings are close, check for sticking thermostat or incorrect thermostat application. If problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If display readings are not close, go to next step.
  7. Turn ignition off. Disconnect PCM Blue 80-pin harness connector E-21. PCM is located at right rear of engine compartment. Using DVOM, measure ECT sensor resistance at PCM harness connector E-21 terminal No. 74 (Blue/Red wire) and No. 53 (Green wire). Compare resistance reading with coolant temperature reading. See ENGINE COOLANT TEMPERATURE SENSOR RESISTANCE  table under DTC P0117. If readings are as specified, go to step  12. If readings are not as specified, go to next step.
  8. Check for high resistance in ECT sensor signal circuit or sensor ground circuit between PCM and ECT sensor. See WIRING DIAGRAMS article. Check for poor connections at PCM and ECT sensor harness connections. If problem with wiring is found, go to step  10. If no problem with wiring is found, go to step  11.
  9. Check for cooling system faults (thermostat, water pump, etc.) or coolant leaks. If problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM.
  10. Repair or replace faulty wiring or terminals as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM.
  11. Replace ECT sensor. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM.
  12. Replace and reprogram PCM. See POWERTRAIN CONTROL MODULE REPLACEMENT  under POWERTRAIN CONTROL MODULE. Use scan tool to clear DTC and verify repair.
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