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 connect the special tool test harness (MB991709) in between (All terminals should be connected).
2.Connect the oscilloscope special patterns pickup to camshaft position sensor terminal No. 3.
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. 3.

Alternate Method (Test harness not available)


1.Disconnect the engine-ECU connector and connect the special tool power plant ECU check harness (MB992110) in between.
2.Connect the oscilloscope special pattern pickup to engine-ECU terminal No. 14 (When checking the camshaft position sensor signal wave pattern).
3.Connect the oscilloscope special pattern pickup to engine-ECU terminal No. 08 (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



Description of Wave Patterns



  • The camshaft position sensor serves as to detect the compression top dead center of each cylinder. By observing this signal simultaneously with other control signals, it is possible to identify each cylinder.
  • The crank angle sensor is used to detect the crank angle of each cylinder. While the engine revolves for two cycles, 72 pieces of crank angle sensor High signal (including any missing) will be outputted.

Wave Pattern Observation Points



  • Verify that the wave pattern is shortened as the engine speed rises.

Examples of Abnormal Wave Pattern




  • Example 1

    Wave pattern characteristics

      Rectangular wave will be outputted 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 belt
      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.Connect the oscilloscope special patterns pickup to engine-ECU terminal No. 2 (When checking the No. 1 cylinder).
2.Connect the oscilloscope special patterns pickup to engine-ECU terminal No. 3 (When checking the No. 2 cylinder).
3.Connect the oscilloscope special patterns pickup to engine-ECU terminal No. 18 (When checking the No. 3 cylinder).
4.Connect the oscilloscope special patterns pickup to engine-ECU terminal No. 19 (When checking the No. 4 cylinder).
5.Connect the oscilloscope special patterns pickup to engine-ECU terminal No. 50 (When checking the No. 5 cylinder).
6.Connect the oscilloscope special patterns pickup to engine-ECU terminal No. 51 (When checking the No. 6 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



Description of Wave Patterns
  • Normally the supply voltage is applied, but, if any signal is received from the engine-ECU, the voltage falls to near 0 V as long as the drive signal continues.
  • When the signal from the engine-ECU is stopped, a peak voltage resulting from the counter electromotive force of coil appears and the original supply voltage restores.
  • Injector operation time: Fuel injection period determined by the engine-ECU according to various sensor output values. Injector operation time = Effective injection period + Invalid injection period (invalid injection period: used to compensate for the delayed operation due to decrease in the supplied voltage)
  • Solenoid back electromotive force: When the signal from the engine-ECU is OFF, the injector coil can generate a solenoid back electromotive force (Approximately 50 to 60 V).
  • Power supply voltage: While there is no signal from the engine-ECU, the supply voltage is applied.If this supply voltage is low, the invalid injection period gets longer, and the drive period gets longer as well.

Wave Pattern Observation Points




  • Point A: The level of solenoid back electromotive force:
Solenoid back 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



Measure at the right bank (number 1, 3, 5 cylinders)
  1. Disconnect the intermediate connector, and connect the test harness special tool (MB991658) between the separated connectors.
  2. Connect the oscilloscope probe to each intermediate connector terminal to analyze each cylinder:

  • Terminal No. 2 for the number 1 cylinder.
  • Terminal No. 3 for the number 3 cylinder.
  • Terminal No. 4 for the number 5 cylinder.

Measure at the left bank (number 2, 4, 6 cylinders)
  1. Disconnect the ignition coil connector, and connect the test harness special tool (MB991658) between the separated connectors. (All terminals should be connected.)
  2. Connect the oscilloscope probe to each ignition coil connector terminal No. 2.

Alternate Method (Measure at the engine-ECU)


1.Connect the oscilloscope probe to engine-ECU terminal No. 4. (When checking the No. 1 cylinder.)
2.Connect the oscilloscope probe to engine-ECU terminal No. 5. (When checking the No. 2 cylinder.)
3.Connect the oscilloscope probe to engine-ECU terminal No. 20. (When checking the No. 3 cylinder.)
4.Connect the oscilloscope probe to engine-ECU terminal No. 21. (When checking the No. 4 cylinder.)
5.Connect the oscilloscope probe to engine-ECU terminal No. 52. (When checking the No. 5 cylinder.)
6.Connect the oscilloscope probe to engine-ECU terminal No. 53. (When checking the No. 6 cylinder.)

Standard Wave Pattern



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



Description of Wave Patterns



  • Power transistor ON condition:
    An interval when the power transistor is ON and the primary side of ignition coil is conducted (referred to as "dwell interval") This conduction period gets longer if the battery voltage is low or vice versa so that the primary voltage at ignition can be controlled to a constant level.
  • Power transistor OFF condition:
    This interval corresponds to when the power transistor is OFF and the power transistor drive signal is not outputted from the engine-ECU.

Wave Pattern Observation Points



  • Verify that the power transistor control signal (ignition timing) advances as the engine speed increases.

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) <Except vehicles for Russia>



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.Connect the oscilloscope probe to engine-ECU terminal No. 31, connection terminal No. 32, connection terminal No. 47 and connection terminal No. 48 respectively.

Standard Wave Pattern



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



Description of Wave Patterns



  • A wave pattern momentarily appears at acceleration.
  • When the signal from the engine-ECU is turned OFF, a peak voltage resulting from the counter electromotive force of motor coil appears. In addition, the wave pattern will be disturbed by an inductive electromotive force generated as the motor revolves.

Wave Pattern Observation Points



  • Verify that the standard wave patter appears when the stepper motor operating conditions are met.

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.