Comparison Images EWS Oscilloscope Measurement

Checking data lead from the EWS to the DME/DDE control unit

Oscilloscope measurement with metrology in the DIS

When doing this, proceed as follows:

• Install test adapter between DME/DDE and vehicle wiring harness.
  Proceed in accordance with the wiring diagram.
  On the M73, EWS2 or EWS 3.2: DME1 on the M73, EWS 3.3: First test for DME1, then for DME2
  
  
• Carry out oscilloscope measurement between terminal 31 (control unit) and EWS data lead
  
• Measuring cable: MFK1
  
• Measuring channel: Channel A
  
• Measuring range: +/-20V
  
• Voltage form: =
  
• Frequency range: 40 Hz
  
• Terminal 15 ON
  

Important

During the measurement, the DME/DDE must be connected.

The following illustration shows the oscilloscope image of a measurement on a data lead through which the EWS signal is correctly transmitted.

Signal OK

Note that the statement "OK" only refers to the data lead and the signal form. It is unable to determine whether the transmitted code is correct.

If it is still not possible to start the engine:

EWS 2, EWS 3.2: Conduct a data comparison EWS-DME/DDE

EWS 3.3: Conduct a EWS-DME/DDE match

Signal not OK

The above signal indicates a fault in the DME/DDE.

Continue fault finding in the DME/DDE diagnosis program with the fault symptom "Engine does not start. Work through the test modules offered.

Signal not OK

• U = approximately battery voltage:
  Check wiring and repair if necessary. If the wiring is OK: continue fault finding in DME/DDE
  
• U = approximately battery voltage - 1 V (approx. 1 V lower than battery voltage)
  Control units and wiring are OK. Use diagnosis interrogation to ensure that the EWS is cleared.
  

Signal not OK

The above signal indicates a short to ground or a line break. Check EWS-DME/DDE data link and repair if necessary. If data link is OK, replace EWS control unit.