Air Flow Meter/Sensor: Testing and Inspection

INSPECTION PROCEDURE USING AN OSCILLOSCOPE

VOLUME AIRFLOW SENSOR

Required Special Tool:
- MB991709: Test Harness




Measurement Method
1. Disconnect the volume airflow sensor connector,and connect the test harness special tool (MB991709) in between. (All terminals should be connected.)
2. Connect the oscilloscope probe to volume airflow 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.

Observation conditions
Rev engine, observe T1 and T2 remain equal.

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 airflow sensor is normal.