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Home › Mitsubishi › 2002 › Lancer LS › Repair and Diagnosis › Engine Performance › System › Engine Controls - Self-Diagnostics › Diagnostic Tests › DTC P0125: Insufficient Coolant Temperature For Closed Loop Fuel Control › Diagnostic Procedure

Diagnostic Procedure

CAUTION: To prevent damage to scan tool, always turn ignition switch to LOCK position before connecting or disconnecting scan tool.
  1. Using scan tool, check engine coolant temperature sensor. Connect scan tool to data link connector. Turn ignition on. Get scan tool to the data reading mode for data list item 21: ENGINE COOLANT TEMPERATURE SENSOR. The engine coolant temperature and temperature shown with the scan tool should approximately match. Turn ignition switch to LOCK position. If sensor is not operating properly, go to next step. If sensor is operating properly, it can be assumed the malfunction is intermittent.
  2. Check the sensor output voltage at engine coolant temperature sensor harness connector by backprobing. Do not disconnect engine coolant temperature harness connector. Turn ignition on. Using a DVOM, measure voltage between engine coolant temperature harness connector terminal No. 1 and ground by backprobing. See ENGINE COOLANT TEMPERATURE SENSOR VOLTAGE  table. Turn ignition switch to LOCK position. If voltage is as specified, go to next step. If voltage is not as specified, go to step  5 .
    ENGINE COOLANT TEMPERATURE SENSOR VOLTAGE

    Engine Coolant Temperature - °F (°C) Voltage
    -4 (-20) 3.9-4.5
    32 (0) 3.2-3.8
    68 (20) 2.3-2.9
    104 (40) 1.3-1.9
    140 (60) 0.7-1.3
    176 (80) 0.3-0.9
  3. Check engine coolant temperature sensor harness connector for damage. If connector is in good condition, go to next step. If connector is not in good condition, repair or replace as necessary. After repairs, go to step  14 .
  4. Using scan tool, check engine coolant temperature sensor. Connect scan tool to data link connector. Turn ignition on. Set scan tool to the item reading mode for data list item 21: ENGINE COOLANT TEMPERATURE SENSOR. The engine coolant temperature and temperature shown with the scan tool should approximately match. Turn ignition switch to LOCK position. If sensor is not operating properly, replace ECM or PCM. After replacing ECM or PCM, go to step  14 . If sensor is operating properly, malfunction is intermittent.
  5. Check engine coolant temperature sensor harness connector for damage. If connector is in good condition, go to next step. If connector is not in good condition, repair or replace as necessary. After repairs, go to step  14 .
  6. Disconnect engine coolant temperature sensor harness connector. Turn ignition on. Measure voltage between engine coolant temperature harness connector terminal No. 1 and ground. Voltage should be 4.5-4.9 volts. Turn ignition switch to LOCK position. If voltage is not as specified, go to next step. If voltage is as specified, go to step  8 .
  7. Check ECM harness connector C-115 (M/T) or PCM harness connector C-118 (A/T) for damage. If the connector is in good condition, replace ECM or PCM. After replacing ECM or PCM, go to step  14 . If connector is in good condition, repair or replace as necessary. After repairs, go to step  14 .
  8. Check continuity at engine coolant temperature sensor harness connector. Disconnect engine coolant temperature harness connector. Check continuity between engine coolant temperature harness connector terminal No. 2 and ground. Resistance should be less than 2 ohms. If continuity is as specified, go to step  11 . If continuity is not as specified, go to next step.
  9. Check ECM harness connector C-115 (M/T) or PCM harness connector C-118 (A/T) for damage. If connector is in good condition, go to next step. If connector is not in good condition, repair or replace as necessary. After repairs, go to step  14 .
  10. Check for harness damage between engine coolant temperature sensor harness connector terminal No. 2 and ECM harness connector C-115 terminal No. 92 (M/T) or PCM harness connector C-114 terminal No. 57 (A/T). If wiring harness is in good condition, replace ECM or PCM. After replacing ECM or PCM, go to step  14 . If wiring harness is not in good condition, repair wiring harness. After repairs, go to step  14 .
  11. Check engine coolant temperature sensor. Disconnect the engine coolant temperature sensor harness connector. Remove engine coolant temperature sensor. With the temperature sensing portion of engine coolant temperature sensor immersed in hot water, check resistance. See ENGINE COOLANT TEMPERATURE SENSOR RESISTANCE  table. If resistance is as specified, go to next step. If resistance is not as specified, replace engine coolant temperature sensor. Apply 3M AAD (8731) on the thread section of engine coolant temperature sensor. Install engine coolant temperature sensor, and tighten to 15-29 ft. lbs. (19-39 N.m). Then go to step  14 .
    ENGINE COOLANT TEMPERATURE SENSOR RESISTANCE

    Engine Coolant Temperature - °F (°C) k/Ohms
    -4 (-20) 14-17
    32 (0) 5.1-6.5
    68 (20) 2.1-2.7
    104 (40) 0.9-1.3
    140 (60) 0.48-0.68
    176 (80) 0.20-0.36
  12. Check ECM harness connector C-115 (M/T) or PCM harness connector C-118 (A/T) for damage. If connector is in good condition, go to next step. If connector is not in good condition, repair or replace connector. After repairs, go to step  14 .
  13. Check for harness damage between engine coolant temperature sensor harness connector terminal No. 1 and ECM harness connector C-115 terminal No. 83 (M/T) or PCM harness connector C-114 terminal No. 44 (A/T). If wiring harness is in good condition, replace ECM or PCM. After replacing ECM or PCM, go to next step. If wiring harness is not in good condition, repair as necessary. After repairs, go to next step.
  14. Test the OBD-II drive cycle. Carry out a test drive with the drive cycle pattern. See OTHER MONITOR  under VERIFYING REPAIRS. Check for DTCs. If DTC P0125 is output, repeat diagnosis. If DTC P0125 is not output, inspection is complete.
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