Air Flow Meter/Sensor: Testing and Inspection

INSPECTION PROCEDURE USING AN OSCILLOSCOPE

VOLUME AIR FLOW SENSOR

Required Special Tool:
- MB91709: Test Harness Set

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 No.3.

Alternate method (Test harness not available)

Connect the oscilloscope probe to ECM terminal No.90.

Connect the oscilloscope probe to PCM terminal No.65.

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.