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

Alternate Method (Test harness not available)


1.Connect the oscilloscope special pattern pickup to engine-ECU terminal SGC (When checking the camshaft position sensor signal wave pattern.)
2.Connect the oscilloscope special pattern pickup to engine-ECU terminal SGT (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



  • Verify that the sensor signal frequency increases as the engine speed rises.

Examples of Abnormal Wave Patterns




  • Example 1

    Wave pattern characteristics

      Rectangular wave pattern is output even when the engine is not started.

    Cause of problem

      Sensor interface malfunction


  • Example 2

    Wave pattern characteristics

      Wave pattern is displaced to the left or right.

    Cause of problem

      Loose timing belt
      Abnormality in sensor disk

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. 1, of the suction control valve connector.

Alternate Method (Test harness not available)


1.Connect the oscilloscope special pattern pickup to engine-ECU terminal SCV+.

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.