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Home › Mitsubishi › 1998 › Montero › Repair and Diagnosis › Engine Performance › System › Engine Controls - Tests W/Codes › DTC Tests › DTC P0170: Fuel Trim Malfunction

DTC P0170: Fuel Trim Malfunction

NOTE: On vehicles equipped with California emissions, this test applies to right bank diagnostics only. For terminal identification, see TERMINAL IDENTIFICATION . For circuit and wire color identification, see WIRING DIAGRAMS article.
  1. Using a thermometer, check engine compartment ambient temperature. Using scan tool, read IAT sensor temperature (item 13). Compare both readings. If readings are not about the same, go to DTC P0110  test. If readings are about the same, go to next step.
  2. Using a thermometer, check engine compartment ambient temperature. Using scan tool, read ECT sensor temperature (item 21). Compare both readings. If readings are not about the same, go to DTC P0115  test. If readings are about the same, go to next step.
  3. Using scan tool, read BARO sensor pressure (item 25). See DTC P0170 BARO PRESSURE SENSOR SPECIFICATIONS  table. If pressure is not as specified, go to DTC P0105  test. If pressure is as specified, go to next step.
    DTC P0170 BARO PRESSURE SENSOR SPECIFICATIONS

    Altitude Ft. (M) Pressure In. Hg
    0 (0) 14.65
    1969 (600) 13.78
    3937 (1200) 12.76
    5906 (1800) 11.75
  4. Ensure engine coolant temperature is at 68°F (20°C). Disconnect each fuel injector connector. Using DVOM, check resistance across fuel injector terminals. If resistance is not 13-16 ohms replace fuel injector(s). Go to step 14). If resistance is as specified, go to next step.
  5. Inspect wiring harness between each fuel injector and PCM. Repair wiring harness as necessary. Go to step 14). If wiring harness is okay, go to next step.
  6. Inspect each fuel injector and PCM connector for damage. Repair or replace connectors as necessary. Go to step 14). If connectors are okay, go to next step.
  7. Check fuel pressure. See FUEL PRESSURE under FUEL SYSTEM in BASIC TESTING article. Repair fuel system as necessary. Go to step 14). If fuel pressure is okay, go to next step.
  8. Using scan tool, read long term fuel trim (item 81). If fuel trim value is more than zero, go next step. If fuel trim value is less than zero, go to step 12).
  9. Check airflow into intake system. Repair or replace intake system components as necessary. Go to step 14). If airflow is okay, go to next step.
  10. Using scan tool, read VAF sensor frequency (item 12). Frequency should be 25-51 Hz at idle. Frequency at 2500 RPM should be 80-120 Hz on 2.4L or 74-114 Hz on 3.0L. If frequencies are not as specified, replace VAF sensor. Go to step 14). If frequencies are as specified, go to next step.
  11. Inspect following items:
    • Check fuel injectors for clogging.
    • Check fuel filter and fuel lines for clogging.
    • Check fuel pump performance. See FUEL PUMP PERFORMANCE table under FUEL SYSTEM in BASIC TESTING article.
    • Check exhaust system for leaks at HO2S, exhaust manifold, front pipe etc.
    • Check fuel for contamination.

    Repair or replace item(s) as necessary. Go to step 14). If no faults are found, replace PCM. Go to step 14).

  12. Using scan tool, read VAF sensor frequency (item 12). Frequency should be 25-51 Hz at idle. Frequency at 2500 RPM should be 80-120 Hz on 2.4L or 74-114 Hz on 3.0L. If frequencies are not as specified, replace VAF sensor. Go to step 14). If frequencies are as specified, go to next step.
  13. Inspect following items:
    • Check fuel injectors for leaks.
    • Check fuel for contamination.

    Repair or replace item(s) as necessary. Go to next step. If no faults are found, replace PCM. Go to next step.

  14. Road test vehicle and attempt to duplicate conditions that caused original complaint. Recheck for DTCs. If no DTCs are displayed, test is complete.
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