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Home >> Mitsubishi >> 2002 >> Lancer ES, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0171: System Too Lean >> 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. Check for exhaust leaks. If there are no leaks, go to next step. If there are any leaks, repair as necessary. After repairs, go to step  14 .
  2. Check for intake system vacuum leaks. If there are no leaks, go to next step. If there are any leaks, repair as necessary. After repairs, go to step  14 .
  3. Using scan tool, check volume airflow sensor. Connect scan tool to data link connector. Start an operate engine at idle. Set scan tool to the data reading mode for data list item 12: VOLUME AIRFLOW SENSOR. Warm up engine to normal operating temperature of 176-205°F (80-96°C). When idling, data should be 20-46 Hz (1.3-3.3 grams per second). When engine speed is 2500 RPM, data should be 70-110 Hz (6.6-10.2 grams per second). Turn ignition switch to LOCK position. If sensor is operating properly, go to next step. If sensor is not operating properly, go to DTC P0101: VOLUME AIRFLOW CIRCUIT RANGE/PERFORMANCE PROBLEM  .
  4. Using scan tool, check intake air temperature sensor. Turn ignition on. Set scan tool to the data reading mode for data list item 13: INTAKE AIR TEMPERATURE SENSOR. The intake air temperature and temperature shown with the scan tool should approximately match. Turn ignition switch to LOCK position. If sensor is operating properly, go to next step. If sensor is not operating properly, go to DTC P0111: INTAKE AIR TEMPERATURE CIRCUIT MALFUNCTION  , DTC 0112: INTAKE AIR TEMPERATURE CIRCUIT LOW INPUT  and DTC P0113: INTAKE AIR TEMPERATURE CIRCUIT HIGH INPUT  .
  5. Using scan tool, check engine coolant temperature sensor. Turn ignition on. Set 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 operating properly, go to next step. If sensor is not operating properly, go to DTC P0116: ENGINE COOLANT TEMPERATURE CIRCUIT RANGE/PERFORMANCE PROBLEM  , DTC P0117: ENGINE COOLANT TEMPERATURE CIRCUIT LOW INPUT  or DTC P0118: ENGINE COOLANT TEMPERATURE CIRCUIT HIGH INPUT  .
  6. Using scan tool, check barometric pressure sensor. Turn ignition on. Set scan tool to the data reading mode for data list item 25: BAROMETRIC PRESSURE SENSOR. See BAROMETRIC PRESSURE SENSOR DATA  table. Turn ignition switch to LOCK position. If sensor is operating properly, go to next step. If sensor is not operating properly, go to DTC P0106: BAROMETRIC PRESSURE CIRCUIT RANGE/PERFORMANCE PROBLEM  , DTC P0107: BAROMETRIC PRESSURE CIRCUIT LOW INPUT  or DTC P0108: BAROMETRIC PRESSURE CIRCUIT HIGH INPUT  .
    BAROMETRIC PRESSURE SENSOR DATA

    Altitude - Feet (Meters) Pressure
    0 (0) 101 kPa
    1969 (600) 95 kPa
    3937 (1200) 88 kPa
    5906 (1800) 81 kPa
  7. Check fuel injector harness connectors B-17 (Cyl. No. 4), B-18 (Cyl. No. 3), B-20 (Cyl. No. 2) and B-22 (Cyl. No. 1) at injectors for damage. Repair or replace as necessary. After repairs, go to step  14 . If connector is in good condition, go to next step.
  8. Check fuel injectors. Disconnect each fuel injector connector. Measure resistance between each injector terminals No. 1 and 2. Standard value is 13-16 ohms at 68°F (20°C). If resistance is as specified, go to next step. If resistance is not as specified, replace the injector. After repairs, go to step  14 .
  9. Check connector ECM harness connector C-121 (M/T) or PCM harness connector C-120 (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 fuel injector connector and ECM (M/T) or PCM (A/T) harness connector. See INJECTOR CONTROL CIRCUIT IDENTIFICATION  table. If wiring harness is in good condition, go to next step. If wiring harness is not in good condition, repair as necessary. After repairs, go to step  14 .
  11. Check fuel pressure. If fuel pressure is normal, go to next step. If fuel pressure is not normal, repair or replace as necessary. After repairs, go to step  14 .
  12. Check for entry of foreign matter (water, kerosene, etc.) into fuel. If there are no contaminations, go to next step. If there are any contaminations, replace fuel. After replacing fuel, go to step  14 .
  13. Replace affected fuel injector. Carry out a test drive with the drive cycle pattern. See FUEL TRIM MONITOR  under VERIFYING REPAIRS. Check for DTCs. If DTC P0171 is output, replace ECM or PCM. After repairs, go to next step. If DTC P0171 is not output, malfunction is intermittent.
  14. Test the OBD-II drive cycle. Carry out a test drive with the drive cycle pattern. See FUEL TRIM MONITOR  under VERIFYING REPAIRS. Check for DTCs. If DTC P0171 is output, repeat diagnosis. If DTC P0171 is not output, inspection is complete.
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