Air Flow Meter/Sensor: Testing and Inspection

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 volume air flow sensor connector terminal 3.

Alternate method (Test harness not available)
1. Connect the analyzer special patterns pickup to ECM terminal 90.





Observation conditions





Standard wave pattern





Wave Pattern Observation Points

Observation Conditions (pattern changes with engine speed changes.)
Check to be sure 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. However, when an ignition leak occurs during acceleration, the wave pattern will be distorted temporarily, even if the volume air flow sensor is normal.