Oscilloscope Patterns and Waveforms

EGR VALVE (STEPPER MOTOR)

Required Special Tools:
- MB991658: Test Harness
- MB991923: Power Plant ECU Check Harness

Measurement Method

1. Disconnect the EGR valve connector, and connect the test harness special tool (MB991658) between the separated connector (All terminals should be connected).
2. Connect the oscilloscope probe to the EGR valve connector terminal No. 1, terminal No. 3, terminal No. 4, terminal No. 6 respectively.

Alternate method

1. Disconnect all ECM [M/T] connectors or PCM [A/T] connectors. Connect the check harness special tool (MB991923) between the separated connectors.

2. Connect the oscilloscope probe to check harness terminal No. 124, No. 130, No. 136 and No. 142.

Standard Wave Pattern:

Wave Pattern Observation Points
1. Check that the standard wave pattern appears when the EGR valve is operating.

Point A: Presence or absence of induced electromotive force from the motor turning. (Refer to abnormal wave pattern.)

Point B: Height of coil back electromotive force

Examples of Abnormal Wave Patterns

Example 1
Cause of problem
- Malfunction of motor. (Motor is not operating.)

Wave pattern characteristics
- Induced electromotive force from the motor turning does not appear.

Example 2
Cause of problem
- Open circuit in the line between the EGR valve and the ECM [M/T] or the PCM [A/T].

Wave pattern characteristics
- Current is not supplied to the motor coil on the open circuit side. (Voltage does not drop to 0 volt.) Furthermore, the induced electromotive force wave pattern at the normal side is slightly different from the normal wave pattern.