Component Tests and General Diagnostics
INSPECTION PROCEDURE USING AN OSCILLOSCOPEVOLUME AIRFLOW SENSOR
Required Special Tool:
MB991709: Test Harness Set
Measurement Method
1. Disconnect the volume airflow sensor connector, and connect the test harness special tool (MB991709) in between. (All terminals should be connected.)
2. Connect the oscilloscope probe to volume airflow sensor connector terminal No. 3.
Alternate method (Test harness not available)
1. Connect the oscilloscope probe to ECM terminal No. 90.
Standard Wave Pattern
Wave Pattern Observation Points
Check that cycle time T becomes shorter and the frequency increases when the engine speed is 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
- Damaged rectifier or vortex generation column.
Wave pattern characteristics
- Unstable wave pattern with non-uniform frequency. An ignition leak will distort the wave pattern temporarily, even if the volume airflow sensor is normal.
CAMSHAFT POSITION SENSOR AND CRANKSHAFT POSITION SENSOR
Required Special Tools:
MB991709: Test Harness Set
MB998478: Test Harness
Measurement Method
1. Disconnect the camshaft position sensor connector, and connect the test harness special tool (MB991709) in between. (All terminals should be connected.)
2. Connect the oscilloscope probe to camshaft position sensor connector terminal No. 2.
3. Disconnect the crankshaft position sensor connector, and connect the test harness special tool (MD998478) in between.
4. Connect the oscilloscope probe to crankshaft position sensor connector terminal No. 2. (black clip of special tool).
Alternate method (Test harness not available)
1. Connect the oscilloscope probe to ECM terminal No. 88. (Check the camshaft position sensor signal wave pattern.)
2. Connect the oscilloscope probe to ECM terminal No. 89. (Check the crankshaft position sensor signal wave pattern.)
Standard Wave Pattern
Wave Pattern Observation Points
Check that cycle time T 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 Tool:
MB991348: Test Harness Set
Measurement Method
1. Disconnect the injector connector, and connect the test harness special tool (MB991348) in between. (All terminals should be connected.)
2. Connect the oscilloscope probe to injector connector terminal No. 2.
Alternate method (Test harness not available)
1. Connect the oscilloscope probe to ECM terminal No. 1. (When checking the number 1 cylinder.)
2. Connect the oscilloscope probe to ECM terminal No. 14. (When checking the number 2 cylinder.)
3. Connect the oscilloscope probe to ECM terminal No. 2. (When checking the number 3 cylinder.)
4. Connect the oscilloscope probe to ECM terminal No. 15. (When checking the number 4 cylinder.)
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.
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.
IGNITION COIL AND IGNITION POWER TRANSISTOR
Required Special Tool:
MB991348: Test Harness Set
Measurement Method
1. Disconnect the ignition coil connector, and connect test harness special tool, MB991348, in between. (All terminals should be connected.)
2. Connect the oscilloscope probe to ignition coil connector terminal No. 3.
Alternate method (Test harness not available)
1. Connect the oscilloscope probe to the ECM terminal No. 10 (for number 1 - number 4), terminal No. 23 (for number 2 - number 3).
Standard Wave Pattern
Wave Pattern Observation Points
Point: Condition of wave pattern build-up section and maximum voltage (Refer to abnormal wave pattern examples 1 and 2.)
Examples of Abnormal Wave Patterns
Example 1 (Wave pattern during engine cranking)
Cause of problem
- Open-circuit in ignition primary circuit
Wave pattern characteristics
- Top-right part of the build-up section cannot be seen, and voltage value is approximately 2 volts too low.
Example 2 (Wave pattern during engine cranking)
Cause of problem
- Malfunction in ignition power transistor
Wave pattern characteristics
- Power voltage results when the ignition power transistor is ON.