INSPECTION PROCEDURE USING AN OSCILLOSCOPE

1.Disconnect the intake 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. 3.Connect the probe of each channel of the oscilloscope to terminal No. 3 of the intake camshaft position sensor connector and terminal No. 3 of the crank angle sensor connector, respectively.

Description of Wave Patterns

• The intake 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.
  

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

1.Disconnect the exhaust 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. 3.Connect the probe of each channel of the oscilloscope to terminal No. 3 of the exhaust camshaft position sensor connector and terminal No. 3 of the crank angle sensor connector, respectively.

• The exhaust camshaft position sensor serves as to detect the position of the exhaust cam shaft and outputs one pulse per revolution of cam shaft corresponding to the cut provided on the exhaust-side cam shaft.
  
• Whether retardation or advance can be defined as a more or less difference in time from when the crank angle sensor output wave falls to when the exhaust camshaft position sensor output wave rises or falls.
  

  note	At a maximum retardation the fall of the exhaust camshaft position sensor output wave retards approximately 35°.

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

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.

• 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)
  
• Counter electromotive force in the solenoid coil: When the signal from the engine-ECU is OFF, the injector coil can generate a counter electromotive force (Approximately 65 to 75 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.
  

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.

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. 2 of the ignition coil connector. 3.To verify the ignition advance angle, observe it simultaneously with the crank angle sensor output signals.

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.
  

Wave pattern characteristics The voltage is low. Cause of problem Open-circuit in the ignition primary circuit.

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.

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.
  

Wave pattern characteristics Induced electromotive force from the motor revolution dose not appear, or is very small. Coil’s counter electromotive force does not appear, or is very small. Cause of problem Faulty motor operation (motor is not revolving) 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.