Oscilloscope Check

IDLE AIR CONTROL MOTOR (STEPPER MOTOR)

Required Special Tool:
MB991709: Test Harness Set

Measurement Method
1. Disconnect the idle air control motor connector, and connect the test harness special tool (MB991709) in between. (All terminals should be connected.)




2. Connect the oscilloscope probe to the idle air control motor connector terminal No. 1, terminal No. 3, terminal No. 4 and terminal No. 6 respectively.

Alternate method (Test harness not available)
1. Connect the oscilloscope probe to the ECM terminal No. 4, terminal No. 5, terminal No. 17 and terminal No. 18 respectively.







Standard Wave Pattern

Wave Pattern Observation Points
Check that the standard wave pattern appears when the idle air control motor 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 idle air control motor 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.