INSPECTION PROCEDURE USING OSCILLOSCOPE


The output signals of the sensors and the conditions of the actuation signals of the actuators can be inspected visually by observing the waveforms on the oscilloscope.

CAMSHAFT POSITION SENSOR AND CRANK ANGLE SENSOR

Measurement Method

1.Disconnect the camshaft position sensor connector and connect the special tool test harness (MB991658) in between (All terminals should be connected).
2.Connect the oscilloscope special pattern pickup to camshaft position sensor terminal No. 3.
3.Disconnect the crank angle sensor intermediate connector and connect the special tool test harness (MB991709) in between.
4.Connect the oscilloscope special pattern pickup to crank angle sensor terminal No. 2.

Alternate Method (Test harness not available)
1.Connect the oscilloscope special pattern pickup to engine-ECU terminal No. 57 (When checking the camshaft position sensor signal wave pattern.)
2.Connect the oscilloscope special pattern pickup to engine-ECU terminal No. 58 (When checking the crank angle sensor signal wave pattern.)

Standard Wave Pattern



Observation conditions
Function
 Special patterns
Pattern height
 Low
Pattern selector
 Display
Engine speed
 Idle


Wave Pattern Observation Points

  • Check that cycle time T becomes shorter when the engine speed increases.

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 disk

    Wave pattern characteristics

      Wave pattern is displaced to the left or right.

SUCTION CONTROL VALVE

Measurement Method

1.Disconnect the suction control valve connector, and then connect the special tool test harness (MB991658) in between (All terminals should be connected).
2.Connect the oscilloscope special pattern pickup to terminal No. 2, of the suction control valve connector.

Alternate Method (Test harness not available)
1.Connect the oscilloscope special pattern pickup to engine-ECU terminal No. 37.

Standard Wave Pattern



Observation conditions
Function
 Special patterns
Pattern height
 Variable
Variable knob
 Adjust while viewing the wave pattern
Pattern selector
 Display
Engine
 Idle

Wave Pattern Observation Points

When fuel pressure rises while the engine load is high, the driving time of the suction control valve becomes short