Air Flow Meter/Sensor: Testing and Inspection
INSPECTION PROCEDURE USING AN OSCILLOSCOPE VOLUME AIR FLOW SENSORRequired Special Tool:
- MB991709: Test Harness
Measurement Method
1. Disconnect the volume air flow sensor connector, and connect the test harness special tool (MB991 709) in between. (All terminals should be connected.)
2. Connect the oscilloscope probe to volume air flow sensor connector terminal 3.
Alternate method (Test harness not available)
1. Connect the oscilloscope probe to ECM terminal 61.
1. Connect the oscilloscope probe to PCM terminal 65.
Standard Wave Pattern:
Standard Wave Pattern:
Wave Pattern Observation Points
1. 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
Sensor interface malfunction.
- 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. An ignition leak will distort the wave pattern temporarily, even if the volume air flow sensor is normal.