Code 12: Airflow Sensor

NOTE: For component terminal identification, see TERMINAL IDENTIFICATION . For wiring diagrams, see WIRING DIAGRAMS article in the ENGINE PERFORMANCE 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 tester, go to step 3).

If using scan tester, 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.
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
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA

Warm vehicle to normal operating temperature. Ensure headlights and accessories are off. Ensure steering wheel is in straight-ahead position. Using scan tester, 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
1.8L	23-49	51-91

Disconnect AFS connector and MFI relay connector. Using DVOM, check for continuity between AFS connector terminal No. 4 and MFI relay connector terminal No. 3. If continuity does not exist, repair wiring harness as necessary. If continuity exists, go to next step.
Using DVOM, check for continuity between chassis ground and AFS connector terminal No. 5. If continuity does not exist, repair wiring harness as necessary. If continuity exists, go to next step.

Disconnect AFS connector and ECM connector. Using DVOM, check for continuity between specified AFS connector terminal and ECM connector terminal. See AFS-TO-ECM 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-ECM WIRING HARNESS TERMINAL IDENTIFICATION

Application	AFS Terminal No.	ECM Terminal No.
All Models	3	70
7		19

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 ECM. 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 article in the ENGINE PERFORMANCE Section.
Disconnect AFS connector. Turn ignition switch to ON position. Using DVOM, check voltage between specified terminal and chassis ground. If system voltage does not exist, repair wiring harness as necessary. If system voltage exists, go to next step.
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.
Using DVOM, check for continuity between AFS connector terminal No. 5 and chassis ground. If continuity does not exist, repair wiring harness as necessary. Go to next step.
Disconnect AFS connector and ECM connector. Using DVOM, check for continuity between AFS connector terminal No. 7 and ECM connector terminal No. 57. 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 article in the ENGINE PERFORMANCE Section.