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 intermediate connector and connect the special tool Test harness (MB991658) in between.
4.Connect the oscilloscope special patterns pickup to crank angle sensor terminal No. 2.

Alternate Method (Test harness not available)
1.Connect the oscilloscope special patterns pickup to engine-A/T-ECU terminal No. 71 (When checking the camshaft position sensor signal wave pattern).
2.Connect the oscilloscope special patterns pickup to engine-A/T-ECU terminal No. 70 (When checking the crank angle sensor signal wave pattern).

Standard Wave Pattern

Observation condition
Function
 Special patterns
Pattern height
 Low
Pattern selector
 Display
Engine speed
 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 belt
      Abnormality in sensor disk
    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 each injector connector in turn.

Alternate Method (Test harness not available)
1.Connect the oscilloscope special patterns pickup to engine-A/T-ECU terminal No. 1 (When checking the No. 1 cylinder).
2.Connect the oscilloscope special patterns pickup to engine-A/T-ECU terminal No. 5 (When checking the No. 2 cylinder).
3.Connect the oscilloscope special patterns pickup to engine-A/T-ECU terminal No. 14 (When checking the No. 3 cylinder).
4.Connect the oscilloscope special patterns pickup to engine-A/T-ECU terminal No. 21 (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 doesn’t 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 (Test harness not available)
1.Connect the oscilloscope probe to engine-A/T-ECU terminal No. 31. (When checking the number 1 cylinder.)
2.Connect the oscilloscope probe to engine-A/T-ECU terminal No. 32. (When checking the number 2 cylinder.)
3.Connect the oscilloscope probe to engine-A/T-ECU terminal No. 35. (When checking the number 3 cylinder.)
4.Connect the oscilloscope probe to engine-A/T-ECU terminal No. 52. (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
    • Cause of problem
      Open-circuit in ignition primary circuit
    Wave pattern characteristics
      Voltage value is too low.

EGR VALVE (STEPPER MOTOR)

Measurement Method


  1. Disconnect the EGR valve connector, and connect the special tool test harness (MB991658) in between.
  2. Connect the oscilloscope probe to the EGR valve-side 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 engine-A/T-ECU terminal No. 3, connection terminal No. 12, connection terminal No. 19, and connection terminal No. 26 respectively.

Standard Wave Pattern

Observation condition
Function
 Special patterns
Pattern height
 High
Pattern selector
 Display
Engine
 Ignition switch: OFF → ON


Wave pattern Observation Points
Check that the standard wave pattern appears when the EGR control servo is operating.
Point A: Presence or absence of induced electromotive force from the motor turning. (Refer to the abnormal wave pattern.)
Contrast with standard wave pattern
 Probable cause
Induced electromotive force does not appear or is extremely small.
 Motor is malfunctioning
Point B: Height of coil reverse electromotive force
Contrast with standard wave pattern
 Probable cause
Coil reverse electromotive force does not appear or is extremely small.
 Short in the coil

Examples of Abnormal Wave Patterns



  • Example 1
    • Cause of problem
      Sensor interface malfunction. (Motor is not operating)
    Wave pattern characteristics
      Induced electromotive force from the motor turning dose not appear.
  • Example 2
    • Cause of problem
      Open circuit in the line between the EGR valve and the engine-A/T-ECU.
    Wave pattern characteristics
      Current is not supplied to the motor coil on the open circuit side. (Voltage dose not drop to 0 V.)
      Furthermore, the induced electromotive force waveform at the open circuit side is slightly different from the normal waveform.