Air Flow Meter/Sensor: Testing and Inspection

VOLUME AIR FLOW SENSOR

OPERATION
- The volume air flow sensor is incorporated within the air cleaner, it functions to convert the amount of engine air intake to pulse signals of a frequency proportional to the amount of engine air intake, and to input those signals to the engine control module. The engine control module then, based upon those signals, calculates the amount of fuel injection, etc.
- The power for the volume air flow sensor is supplied from the MFI relay to the volume air flow sensor, and is grounded at the engine control module. The volume air flow sensor, by intermitting the flow of the 5 V voltage applied from the engine control module, produces pulse signals.

TROUBLESHOOTING HINTS
Hint 1:
If the engine sometimes stalls, try starting the engine and shaking the volume air flow sensor harness. If the engine then stalls, incorrect or improper contact of the volume air flow sensor connector is the probable cause.
Hint 2:
If the volume air flow sensor output frequency is any value other than zero when the ignition switch is switched ON (but the engine is not started), a malfunction of the volume air flow sensor or of the engine control module is the probable cause.
Hint 3:
If idling is possible even though the volume air flow sensor output frequency is outside the standard value, the cause is usually a malfunction other than of the volume air flow sensor.

[Examples]
1. The flow of air within the volume air flow sensor is disturbed. (Air duct disconnection or clogged air cleaner element.)
2. Incomplete combustion inside a cylinder (Malfunction of spark plugs, ignition coil, injectors, compression pressure, etc.)
3. Air is drawn into the intake manifold through a leaking gasket, etc.

INSPECTION

Using Scan Tool





NOTE:
When the vehicle is new [driven approximately 500 km (300 miles) or less], the volume air flow sensor output frequency may be approximately 10% higher than indicated above.





<Volume Air Flow Sensor Reset Signal>

















Wave Pattern Inspection Using an Analyzer Measurement Method
1. Disconnect the volume air flow sensor connector, and connect the special tool (test harness: MB991348) in between. (All terminals should be connected.)
2. Connect the analyzer special patterns pickup to terminal (3) of the volume air flow sensor connector.

Alternative Method (when Test Harness Is Not Available)
Connect the analyzer special patterns pickup to ECM terminal (90).








Standard Wave Pattern





Observation Conditions

Observation conditions (Pattern changes with engine speed changes)

Wave Pattern Observation Points
Check that cycle time T becomes shorter and the frequency increases when the engine speed is increased.

Examples Of Abnormal Wave Patterns
- Example 1
Cause of problem
- Malfunction of sensor interface
Wave pattern characteristics
- Rectangular wave pattern is output even when the engine is not started.





- Example 2
Cause of problem
- Damaged rectifier or vortex generation column
Wave pattern characteristics
- Unstable wave pattern with non-uniform frequency. However, when an ignition leak occurs during acceleration, the wave pattern will be distorted temporarily, even if the volume air flow sensor is normal.




HARNESS INSPECTION

STEP 1. Check for continuity between the volume air flow sensor and the MFI relay.
- MFI relay connector: Disconnected
- Volume air flow sensor connector: Disconnected

NOTE:
- Touch the ohmmeter probes to both ends of the harness.

OK: GO TO STEP 2
NG: Repair the harness. (A4 - B2)





STEP 2. Check for continuity in the ground circuit.
- Volume air flow sensor connector: Disconnected

OK: GO TO STEP 3
NG: Repair the harness. (A5 - 92)





STEP 3. Check for an open or short-circuit between the volume air flow sensor and the engine control module.
- Volume air flow sensor connector: Disconnected
- Engine control module connector: Disconnected

OK: GO TO STEP 4
NG: Repair the harness. (A3 - 90, A7 - 19)





STEP 4. Measure the applied voltage
- Volume air flow sensor connector: Disconnected
- Engine control module connector: Connected
- Ignition switch: ON

Voltage (V): 4.8 - 5.2

OK: STOP
NG: Replace the engine control module.