Oscilloscope Patterns and Waveforms

WAVE PATTERN INSPECTION USING AN ANALYZER
^ Ignition coil primary signal.
^ Ignition power transistor control signal

MEASUREMENT METHOD
1. Disconnect the ignition power transistor connector, and connect the special tool test harness: MB991348) in between. (All terminals should be connected.)
2. Connect the analyzer special patterns pickup to ignition power transistor unit connector terminal No. 6.

ALTERNATE METHOD (test harness not available)
1. Connect the analyzer special patterns pickup to ECM terminal No. 10.





STANDARD WAVE PATTERN


WAVE PATTERN OBSERVATION POINTS
Condition of wave pattern build-up section and maximum voltage (Refer to abnormal wave pattern examples 1 and 2.)

Condition of wave pattern Probable cause
build-up section and
maximum voltage

Rises from approx. 2V to
approx. 4.5V at the top-right Normal

2V rectangular wave Open-circuit in ignition primary circuit

Rectangular wave at power voltage Ignition power transistor malfunction

EXAMPLES OF ABNORMAL WAVE PATTERNS





Example 1
Wave pattern during engine cranking

Cause of problem: Open-circuit in ignition primary circuit

Wave pattern characteristics: Top-right part of the build-up section cannot be seen, and voltage value is approximately 2V too low.





Example 2
Wave pattern during engine cranking

Cause of problem: Malfunction in ignition power transistor

Wave pattern characteristics: Power voltage results when the ignition power transistor is ON.