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.
4.Connect the oscilloscope special patterns pickup to crank angle sensor terminal No. 2.

Alternate Method (Measure at the engine-ECU or engine-A-M/T-ECU)


1.Disconnect the engine-ECU or engine-A-M/T-ECU connector and connect the special tool Power plant ECU check harness (MB991987) in between.
2.Connect the oscilloscope special patterns pickup to engine-ECU or engine-A-M/T-ECU terminal No. 12 (When checking the camshaft position sensor signal wave pattern).
3.Connect the oscilloscope special patterns pickup to engine-ECU or engine-A-M/T-ECU terminal No. 13 (When checking the crank angle sensor signal wave pattern).

Standard Wave Pattern



Observation condition
Function
Special patterns
Pattern height
Low
Pattern selector
Display
Engine
Idle



Wave Pattern Observation Points


Check that cycle time 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 chain
      Abnormality in sensing ring
    Wave pattern characteristics
      Wave pattern is displaced to the left or right.

INJECTOR



Measurement Method



1.Disconnect the injector connector, and then connect the special tool Test harness set (MB991658) in between (All terminals should be connected).
2.Connect the oscilloscope special patterns pickup to terminal No. 2 of the injector connector.

Alternate Method (Measure at the engine-ECU or engine-A-M/T-ECU)


1.Disconnect the engine-ECU or engine-A-M/T-ECU connector and connect the special tool Power plant ECU check harness (MB991987) in between.
2.Connect the oscilloscope special patterns pickup to engine-ECU or engine-A-M/T-ECU terminal No. 8 (When checking the No. 1 cylinder).
3.Connect the oscilloscope special patterns pickup to engine-ECU or engine-A-M/T-ECU terminal No. 9 (When checking the No. 2 cylinder).
4.Connect the oscilloscope special patterns pickup to engine-ECU or engine-A-M/T-ECU terminal No. 23 (When checking the No. 3 cylinder).
5.Connect the oscilloscope special patterns pickup to engine-ECU or engine-A-M/T-ECU terminal No. 24 (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
Idle



Wave Pattern Observation Points


Point A: Height of solenoid back electromotive force
Contrast with standard wave pattern
Probable cause
Solenoid coil back electromotive force is low or does not appear at all.
Short in the injector solenoid
Point B: Injector drive time


  • The injector drive time will be synchronized with the M.U.T.-III tester display.
  • When the engine is suddenly raced, the drive time will be greatly extended at first, but the drive time will soon match the engine speed.

IGNITION COIL AND POWER TRANSISTOR



Measurement Method



1.Disconnect the ignition coil connector, and connect the special tool Test harness (MB991658) in between (All terminals should be connected).
2.Connect the oscilloscope special patterns pickup to terminal No. 3 of each ignition coil connector in turn.

Alternate Method (Measure at the engine-ECU or engine-A-M/T-ECU)


1.Disconnect the engine-ECU or engine-A-M/T-ECU connector and connect the special tool Power plant ECU check harness (MB991987) in between.
2.Connect the oscilloscope probe to engine-ECU or engine-A-M/T-ECU terminal No. 10. (When checking the number 1 cylinder.)
3.Connect the oscilloscope probe to engine-ECU or engine-A-M/T-ECU terminal No. 25. (When checking the number 2 cylinder.)
4.Connect the oscilloscope probe to engine-ECU or engine-A-M/T-ECU terminal No. 40. (When checking the number 3 cylinder.)
5.Connect the oscilloscope probe to engine-ECU or engine-A-M/T-ECU terminal No. 55. (When checking the number 4 cylinder.)

Standard Wave Pattern



Observation condition
Function
Special patterns
Pattern height
Low
Pattern selector
Display
Engine
Idle



Wave Pattern Observation Points


Point: When the engine speed increases, verify that the power transistor control signal (ignition timing) advances.

Examples of Abnormal Wave Patterns




  • Example
    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 V too low.





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