Air Flow Meter/Sensor: Testing and Inspection
INSPECTION PROCEDURE USING AN OSCILLOSCOPEVOLUME AIR FLOW SENSOR
Measurement Method
1. Disconnect the volume air flow sensor connector, and connect the test harness special tool (MB991709) in between. (All terminals should be connected.)
2. Connect the oscilloscope probe to volume air flow sensor connector terminal 3.
Alternate method Crest harness not available)
Connect the oscilloscope probe to ECM terminal 90.
Connect the oscilloscope probe to PCM terminal 65.
Standard Wave Pattern
Observation conditions
Standard Wave Pattern:
Standard Wave Pattern
Observation conditions
Rev engine, observe T1 and T2 remain equal.
Standard Wave Pattern:
Standard Wave Pattern
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
- 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.