Inspection Procedure Using an Oscilloscope
INSPECTION PROCEDURE USING AN OSCILLOSCOPECAMSHAFT POSITION SENSOR AND CRANKSHAFT POSITION SENSOR
Required Special Tools:
- MB991709: Test Harness
- MB991658: Test Harness
- MB991923: Power Plant ECU Check Harness
Measurement Method
1. Disconnect the camshaft position sensor connector, and connect the test harness special tool (MB991709) between the separated connector (All terminals should be connected).
2. Connect the oscilloscope probe to camshaft position sensor connector terminal No. 2.
3. Disconnect the crankshaft position sensor intermediate connector, and connect the test harness special tool (MB991658) between the separated connector.
4. Connect the oscilloscope probe to crankshaft position sensor intermediate connector terminal No. 2.
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 to check harness terminal No. 104. (Check the camshaft position sensor signal wave pattern.)
3. Connect the oscilloscope to check harness terminal No. 103. (Check the crankshaft position sensor signal wave pattern.)
Standard Wave Pattern:
Standard Wave Pattern:
Wave Pattern Observation Points
1. Check that cycle time becomes shorter when the engine speed increased.
Examples of Abnormal Wave Patterns
Example 1
Cause of problem
- Sensor interface malfunction.
Wave pattern characteristics
- Rectangular wave pattern is output even when the engine is not started.
Example 2
Cause of problem
- Loose timing belt.
- Abnormality in sensor disc.
Wave pattern characteristics
- Wave pattern is displaced to the left or right.
INJECTOR
Required Special Tools:
- MB991658: Test Harness
- MB991923: Power Plant ECU Check Harness
Measurement Method
1. Disconnect the injector connector, and connect the test harness special tool (MB991658) between the separated connector. (All terminals should be connected.)
2. Connect the oscilloscope probe to injector connector terminal No. 2.
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 each check harness connector terminal to analyze each cylinder:
- Terminal No. 153 for the number 1 cylinder.
- Terminal No. 146 for the number 2 cylinder.
- Terminal No. 140 for the number 3 cylinder.
- Terminal No. 139 for the number 4 cylinder.
Standard Wave Pattern:
Standard Wave Pattern:
Wave Pattern Observation Points
Point A: Height of injector coil induced voltage.
Point B: Injector drive time
1. The injector drive time should be synchronized with the scan tool tester display.
2. When the engine is suddenly revved, the drive time will be greatly extended at first, but the drive time will soon return to original length.
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:
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.
IGNITION COIL AND IGNITION POWER TRANSISTOR
Required Special Tools:
- MB991658: Test Harness
- MB991923: Power Plant ECU Check Harness
Measurement Method
1. Disconnect the ignition coil connector, and connect the test harness special tool (MB991658) between the separated connector.
2. Connect the oscilloscope probe to ignition coil connector terminal No. 3.
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 each check harness connector terminal to analyze each cylinder:
- Terminal No. 151 for the number 1 cylinder.
- Terminal No. 143 for the number 2 cylinder.
- Terminal No. 150 for the number 3 cylinder.
- Terminal No. 148 for the number 4 cylinder.
Standard Wave Pattern:
Standard Wave Pattern:
Wave Pattern Observation Points
Point: The power transistor control signal (ignition timing) is advanced when the engine speed is increased.
Examples of Abnormal Wave Patterns
Example 1 (Wave pattern during engine cranking)
- Cause of problem
Open-circuit in ignition primary circuit
- Wave pattern characteristics
Voltage value is too low.