INSPECTION PROCEDURE USING AN 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 insert the special tool test harness (MB991709) in-between the separated connectors (Always mate all the terminals).
2.Disconnect the crank angle sensor connector and insert the special tool test harness (MB991709) in-between the separated connectors (Always mate all the terminals).
3.Connect the probe of each channel of the oscilloscope to terminal No. 3 of the camshaft position sensor connector and terminal No. 3 of the crank angle sensor connector, respectively.

Alternate Method (Measure at the engine-ECU)


1.Disconnect the engine-ECU connector and connect the special tool Power plant ECU check harness (MB992110) in between.
2.Connect the oscilloscope special patterns pickup to engine-ECU connector terminal CPI (when checking the camshaft position sensor signal wave pattern).
3.Connect the oscilloscope special patterns pickup to engine-ECU connector terminal SGT (when checking the crank angle sensor signal wave pattern).

Standard Wave Pattern



Observation condition
Function
Special patterns
Pattern height
Low
Pattern selector
Display
Engine
Continuous idling mode



Description of Wave Patterns




Wave Pattern Observation Points




Examples of Abnormal Wave Pattern




  • Example 1

    Wave pattern characteristics

      Rectangular wave will be output while the engine is not started.

    Cause of problem

      Failed sensor interface


  • Example 2

    Wave pattern characteristics

      Wave pattern is displaced in the forward or backward direction.

    Cause of problem

      Loose timing chain
      Abnormal sensing section

Injector



Measurement Method



1.Disconnect the injector connector and insert the special tool Test harness (MB991658) in-between the separated connectors. (always mate all the terminals.)
2.Connect the oscilloscope probe to terminal No. 2 of the injector connector.

Alternate Method (Measure at the engine-ECU)


1.Disconnect the engine-ECU connector and connect the special tool Power plant ECU check harness (MB992110) in between.
2.Connect the oscilloscope special patterns pickup to engine-ECU connector terminal INJ1 (when checking the No. 1 cylinder).
3.Connect the oscilloscope special patterns pickup to engine-ECU connector terminal INJ2 (when checking the No. 2 cylinder).
4.Connect the oscilloscope special patterns pickup to engine-ECU connector terminal INJ3 when checking the No. 3 cylinder).
5.Connect the oscilloscope special patterns pickup to engine-ECU connector terminal INJ4 (when checking the No. 4 cylinder).

Standard Wave Pattern



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



Description of Wave Patterns

Wave Pattern Observation Points



  • Point A: The level of counter electromotive force of solenoid coil:
Solenoid coil counter electromotive force is low or doesn’t appear at all.
Short-circuit in the injector solenoid


  • Point B: Injector operation time
Operation time
Consistent with the displayed time on M.U.T.-III.
Force an excessive acceleration.
The drive period will once extend greatly, then will be settled to that corresponding to the engine speed.

Ignition coil (power transistor control signal)



Measurement Method



1.Disconnect the ignition coil connector and insert the special tool test harness (MB991658) in-between the separated connectors. (Always mate all the terminals.)
2.Connect the oscilloscope probe to terminal No. 1 of the ignition coil connector.
3.To verify the ignition advance angle, observe it simultaneously with the crank angle sensor output signals.

Alternate Method (Measure at the engine-ECU)


1.Disconnect the engine-ECU connector and connect the special tool Power plant ECU check harness (MB992110) in between.
2.Connect the oscilloscope probe to engine-ECU connector terminal CIL1. (when checking the No. 1 cylinder.)
3.Connect the oscilloscope probe to engine-ECU connector terminal CIL2. (when checking the No. 2 cylinder.)
4.Connect the oscilloscope probe to engine-ECU connector terminal CIL3. (when checking the No. 3 cylinder.)
5.Connect the oscilloscope probe to engine-ECU connector terminal CIL4. (when checking the No. 4 cylinder.)

Standard Wave Pattern



Observation condition
Function
Special patterns
Pattern height
Low
Pattern selector
Display
Engine
Continuous idling mode



Description of Wave Patterns




Wave Pattern Observation Points




Examples of Abnormal Wave Pattern




    Wave pattern characteristics

      The voltage is low.

    Cause of problem

      Open-circuit in the ignition primary circuit.

EXHAUST GAS RECIRCULATION VALVE (STEPPER MOTOR)



Measurement Method



1.Disconnect the exhaust gas recirculation valve connector and insert the special tool test harness (MB991658) in-between the separated connectors. (Always mate all the terminals.)
2.Connect the oscilloscope probe of each channel to either combination of terminal No. 1 and No. 3 or terminal No. 4 and No. 6 of the exhaust gas recirculation valve connector.

Alternate Method (Measure at the engine-ECU)


1.Disconnect the engine-ECU connector and connect the special tool Power plant ECU check harness (MB992110) in between.
2.Connect the oscilloscope probe to engine-ECU connector terminal EGRA and EGRB or connector terminal EGRC and EGRD respectively.

Standard Wave Pattern



Observation condition
Function
Special patterns
Pattern height
High
Pattern selector
Display
Engine
Power supply mode of electric motor switch: OFF → ACC



Description of Wave Patterns




Wave Pattern Observation Points




Examples of Abnormal Wave Pattern




  • Example 1

    Wave pattern characteristics

  1. Induced electromotive force from the motor revolution dose not appear, or is very small.
  2. Coil’s counter electromotive force does not appear, or is very small.

    Cause of problem

  1. Faulty motor operation (motor is not revolving)
  2. Short-circuit in the coil


  • Example 2

    Wave pattern characteristics

      The motor coil is not conducted (voltage does not fall to 0 V), or the waveform of the induced electromotive force is slightly different from the standard one.

    Cause of problem

      Open-circuit in the line between the stepper motor and engine-ECU.