Oscilloscope Test
IDLE AIR CONTROL MOTOR (STEPPER MOTOR)Required Special Tool:
- MB991709: Test Harness
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 1, terminal 3, terminal 4 and terminal 6, respectively.
Alternate method (Test harness not available)
1. Connect the oscilloscope probe to ECM
Standard Wave Pattern:
Standard Wave Pattern
Wave Pattern Observation Points
1. 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.)
CONTRAST WITH STANDARD PROBABLE CAUSE
WAVE PATTERN
Induced electromotive force does Malfunction of motor not appear or is extremely small
Point B:
Height of coil back electromotive force
CONTRAST WITH STANDARD PROBABLE CAUSE
WAVE PATTERN
Coil reverse electromotive force 1 Short in the coil or is extremely does not appear small
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.