DTC 12

Air Flow Sensor Circuit:

To test the Air Flow Sensor, located inside the air cleaner housing proceed as follows.


OSCILLOSCOPE TESTING PROCEDURES:
1. Run engine at idle speed.
2. Engine coolant temperature should be at: 85-95°C (185-205°F), with no electrical accessory loads on.
3. Connect the input probe of the oscilloscope, to the pickup point shown in the circuit diagram, and check the wave form.

Scope Pattern:

If scope pattern is not as depicted in image, continue with the rest of the test procedures before replacing the assembly.

FREQUENCY TESTING PROCEDURES:
1. Warm engine. Coolant temperature should be at: 85-95°C (185-205°F), with no electrical accessory loads on. Connect a Frequency counter (HERTZ counter) between terminal 5 and 3 (do not remove the connector, instead insert a straight pin or needle from the back side of the connector) of the Air Flow Sensor (AFS) connector.
Terminal 5: Sensor ground
Terminal 3: AFS output

2. Measure the frequency across terminals 5 and 3.

Standard Values
23 to 49 Hz at 750 rpm
51 to 91 Hz at 2,000 rpm
Frequency increases as RPM increases

NOTE: If the air flow sensor fails, the intake air volume cannot be measured and as a result, normal fuel injection control is no longer available. However, the vehicle will run using the pre-programmed value.


HARNESS TEST:
1. Disconnect the control relay connector and the air flow sensor connector.
2. Using an ohmmeter, check for continuity between pin 3 of the control relay harness side connector and pin 4 of the air flow sensor connector harness side. There should be continuity.
3. Using an ohmmeter, check for continuity between pin 5 of the air flow sensor connector harness side and ground. There should be continuity.
4. Disconnect ECM connector and check for continuity between pin 19 of the ECU connector harness side and pin 7 of the air flow sensor connector harness side. There should be continuity.
5. Check for continuity between pin 70 of the ECU connector harness side and pin 3 of the air flow sensor connector harness side. There should be continuity.
6. Check for continuity between pin 70 of the ECU connector harness side and ground. There should be no continuity.
7. Check for continuity between pin 19 of the ECU connector harness side and ground. There should be no continuity.
8. Check for continuity between pin 7 of the air flow sensor connector harness side and ground. There should be no continuity.
9. Check for continuity between pin 3 of the air flow sensor connector harness side and ground. There should be no continuity.
10. Reconnect ECU harness connector. Turn ignition switch to ON, engine not running. Measure voltage between pin 3 of air flow sensor connector harness side and ground.

Voltage
4.8 - 5.2 Volts

If any of the previous tests produce unsatisfactory results, the harness will need to be repaired or replaced. Once repairs have been completed, clear the trouble codes and road test the vehicle to confirm that the repair has corrected the problem and the code doesn't return.

If the same trouble code reoccurs, it is possible that there is an intermittent failure of the component or the ECU. Check for looseness at all harness junctions and test for an intermittent failure.