Oscilloscope Check
EGR VALVE (STEPPER MOTOR)Required Special Tool:
- MB991658: Test 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, No. terminal 6 respectively.
Alternate method (Test harness not available)
1. Connect the oscilloscope probe to ECM
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
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.