DTC 12
System Schematic:
To test the Air Flow Sensor, located inside the air cleaner housing. Proceed as follows:
Air Flow Sensor Location:
OSCILLOSCOPE TESTING PROCEDURES:
Scope Pattern:
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.
If scope pattern is not as depicted in image, continue with the rest of the test procedures before replacing the assembly.
VOLTMETER TESTING PROCEDURES:
Air Flow Sensor, Test Hook-up:
1. Warm engine. Coolant temperature should be at: 85-95~C (185-205~F), with no electrical accessory loads on. Connect a voltmeter (do not remove the connector, instead insert a straight pin or needle from the back side of the connector) between terminal 1 and 4 of the Air Flow Sensor (AFS) connector.
Terminal 4: Sensor ground
Terminal 1: AFS output
2. Warm the engine and bring it to a normal idle.
3. Measure the voltage of terminals 1 and 4.
Standard Values
Engine speed(RPM) Output voltage(V)
Idling - 3,000........2.2-3.2
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 1 and 4 (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 4: Sensor ground
Terminal 1: AFS output
2. Measure the frequency across terminals 1 and 4.
Standard Values
Engine speed(RPM) Output frequency (Hz)
Idling.................30-50 Hz
2,000.................50-80 Hz
Racing.................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 air flow sensor connector and Turn on the ignition.
2. Using a voltmeter, measure the terminal voltage between the harness connector terminal 1 and ground.
Voltage: 4.8 - 5.2 Volts.
3. Using a voltmeter, measure the power supply voltage between the harness connector terminal 2 and ground.
Voltage: System Voltage.
4. Turn off the ignition and disconnect the engine control unit. Check for continuity of the ground circuit of the air flow sensor, between the harness connector terminal 4 and ground and engine control unit harness connector 24 and ground.
Continuity: Should Exist
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.