Component Tests and General Diagnostics

OPERATION
- The volume air flow sensor located in the air cleaner converts the engine intake air volume into a pulse signal of frequency proportional to the air volume and inputs it to the engine control module, which then computes the fuel injection rate, etc. based on the input signal.
- The volume air flow sensor power is supplied from the MFI relay to the volume air flow sensor and is grounded in the engine control module. The volume air flow sensor generates a pulse signal as it repeatedly opens and closes between the 5 V voltage supplied from the engine control module and ground.

TROUBLESHOOTING HINTS
Hint 1: If the engine stalls occasionally, crank the engine and shake the volume air flow sensor harness. If the engine stalls, poor contact of the volume air flow sensor connector is suspected.
Hint 2: If the volume air flow sensor output frequency is other than 0 when the ignition switch is turned on (but not starting the engine), faulty volume air flow sensor or engine control module is suspected.
Hint 3: If the engine can be run idle even though the volume air flow sensor output frequency is out of specification, troubles are often found in other than the volume air flow sensor itself. [Examples]
(1) Disturbed volume air flow in the air flow sensor (Disconnected air duct, clogged air cleaner element)
(2) Poor combustion in the cylinder
(Faulty ignition plug, ignition coil, injector, incorrect compression pressure, etc.)
(3) Air leaking into the intake manifold through gap of gasket, etc.
(4) Loose EGR valve seat

INSPECTION











Using Scan Tool
<Volume Air Flow Sensor>

NOTE: When the vehicle is new within initial operation of about 500 km (300 miles)], the volume air flow sensor output frequency may be about 10% higher.





<Volume Air Flow Sensor Reset Signal>







Using Oscilloscope
(1) Run the engine at idle speed.





(2) Connect the probe to the oscilloscope pick-up point as shown in the circuit diagram and check the waveform.

HARNESS INSPECTION





Measure the power supply voltage.
- Connector: Disconnected
Voltage (V): Battery positive voltage (Ignition switch: ON)
OK: GO TO STEP 2
NG: Repair the harness. (A4 - Control relay) or check the control relay.





Measure the terminal voltage.
- Connector: Disconnected
- Ignition switch: ON
Voltage (V): 4.8 - 5.2
OK: GO TO STEP 3
NG: Repair the harness. (A3-61)





Check for continuity of the ground circuit.
- Connector: Disconnected
OK: STOP
NG: Repair the harness. (A5-49)





Check for continuity between the volume air flow sensor and the engine control unit.
- Volume air flow sensor connector: Disconnected
- Engine control module connector: Disconnected
OK: STOP
NG: Repair the harness. (A7-19)