Oscilloscope Patterns and Waveforms

Wave Pattern Inspection Using an Analyzer

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 terminal (3) of the volume air flow sensor connector.

Alternative method (when test harness is not available):
Connect the analyzer special patterns pickup to ECM terminal (90).





Standard wave pattern:
Observation conditions





Wave Pattern

Observation conditions:
Observation conditions (Pattern changes with engine speed changes)





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:
Malfunction of sensor interface
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.