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Code 12: Airflow Sensor

NOTE: For component terminal identification, see TERMINAL IDENTIFICATION  in this article. For appropriate WIRING DIAGRAMS, see WIRING DIAGRAMS  section.
NOTE: Procedures are provided by manufacturer for component testing using an engine analyzer with oscilloscope capability. Refer to manufacturer's operation manual for instructions in use of oscilloscope. If using a scan tool, go to step 3).
  1. If using scan tool, go to step 3). Disconnect Airflow Sensor (AFS) connector. Install Test Harness (MB991348 ) between AFS and AFS connector. Using engine analyzer with oscilloscope capability, connect special patterns probe to AFS connector terminal No. 3.
  2. Start engine. Verify that wave form high frequency and low frequency patterns are of approximately the same length (time). See Fig 1. Verify that wave length decreases and frequency increases as engine RPM increases. If conditions are not as specified, replace AFS. If conditions are as specified, go to step 4).
    Fig 1: Identifying Known Good Airflow Sensor Wave Pattern
    G93I80273Courtesy of MITSUBISHI MOTOR SALES OF AMERICA
  3. Warm vehicle to normal operating temperature. Ensure headlights and accessories are off. Ensure steering wheel is in straight-ahead position. Using scan tool, read Airflow Sensor (AFS) volume (frequency) value. See AIRFLOW SENSOR VALUES  table. Frequency should increase when engine is raced. If values are not as specified, replace AFS. If values are as specified, go to next step.
    AIRFLOW SENSOR VALUES

    Application Hz @ 700 RPM Hz @ 2000 RPM
    Expo & Summit Wagon 18-44 43-83
    Galant 18-44 64-104
    (SOHC) 21-47 28-54
    (DOHC) 42-82 45-85
    Pickup 40-60 85-105
  4. On Galant, go to step 8). On all other models, disconnect AFS connector and MFI relay connector. Using DVOM, check for continuity between specified AFS connector terminal and MFI relay connector terminal. See AFS-TO-MFI RELAY TERMINAL WIRING HARNESS IDENTIFICATION  table. If continuity does not exist, repair wiring harness as necessary. If continuity exists, go to next step.
    AFS-TO-MFI RELAY TERMINAL WIRING HARNESS IDENTIFICATION

    Application AFS Terminal No. MFI Relay Terminal No.
    All Models 4 3
  5. Using DVOM, check for continuity between chassis ground and AFS connector terminal No. 5 (terminal No. 4 on Galant). If continuity does not exist, repair wiring harness as necessary. If continuity exists, go to next step.
  6. Disconnect AFS connector and PCM connector. Using DVOM, check for continuity between specified AFS connector terminal and PCM connector terminal. See AFS-TO-PCM WIRING HARNESS TERMINAL IDENTIFICATION  table. If continuity does not exist on specified circuit(s), repair appropriate circuit for open or short to ground as necessary. If continuity exists, go to next step.
    AFS-TO-PCM WIRING HARNESS TERMINAL IDENTIFICATION

    Application AFS Terminal No. PCM Terminal No.
    All Models 3 70
    " 7 19
  7. Turn ignition switch to ON position. Using DVOM, check voltage between chassis ground and AFS harness connector terminal No. 3. If voltage is not 4.8-5.2 volts, replace PCM. If voltage is as specified, condition required to set trouble code is not present at this time. Test is complete. Intermittent problem may exist. See TESTS W/O CODES - 2.4L article.
  8. Disconnect AFS connector. Turn ignition switch to ON position. Using DVOM, check voltage between AFS connector terminal No. 4 and chassis ground. If system voltage does not exist, repair wiring harness as necessary. If system voltage exists, go to next step.
  9. With ignition switch in ON position, use DVOM to check voltage between terminal No. 3 and chassis ground. If voltage is not 4.8-5.2 volts, repair wiring harness as necessary. If voltage is as specified, go to next step.
  10. Using DVOM, check for continuity between AFS connector terminal No. 5 and chassis ground. If continuity does not exist, repair wiring harness as necessary. If continuity exists, go to next step.
  11. Disconnect AFS connector and PCM connector. Using DVOM, check for continuity between specified AFS connector terminal and PCM connector terminal. See PCM-TO-AFS WIRING HARNESS TERMINAL IDENTIFICATION  table. If continuity does not exist on specified circuit(s), repair appropriate circuit for open or short to ground as necessary. If continuity exists, condition required to set trouble code is not present at this time. Test is complete. Intermittent problem may exist. See TESTS W/O CODES - 2.4L article.
    PCM-TO-AFS WIRING HARNESS TERMINAL IDENTIFICATION

    Application PCM Terminal No. AFS Terminal No.
    All Models 57 7
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