Diagnostic Test

TESTING CAN BUS USING THE MOPAR SCOPE 

For a complete CAN C BUS SYSTEM wiring diagram, refer to the appropriate system wiring diagram  .

1. Connect the black pin for each test lead to Chassis ground. Connect the blue lead to CAN (+) and the red lead to CAN (-) for the circuits to be tested.

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2. Start the Mopar Scope.
3. Turn the ignition on.
   NOTE:

   When connected to the vehicle harness correctly, the LEDs on the breakout box will light up to indicate that there is activity on the bus.

4. A waveform should appear.

   The image below is of a normal CAN bus waveform using the Mopar Scope.

   DESCRIPTION	MEASUREMENT
   CHANNEL A	10 volts
   CHANNEL B	10 volts
   TIME BASE	50 μs/div [microseconds / division control]
   ZOOM / VIEW	X1 - HORIZONTAL & VERTICAL

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   NOTE:

   The waveform should reveal that data is being exchanged continuously along the CAN bus and the peak voltages are correct.

5. Determine the type of CAN-C waveform fault the vehicle presently has from below:
   • (+) Short To Ground 

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   • (-) Short To Ground 

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   • (+) Short To Voltage 
     NOTE:

     Channel A and B voltage measurements taken at the 20 V range, measurements taken at 10 V range would display a Channel overrange  message.

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   • (-) Short To Voltage 
     NOTE:

     Channel A and B voltage measurements taken at the 20 V range, measurements taken at 10 V range would display a Channel overrange  message.

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   • Short Together 

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   • (+) Circuit Open 
     NOTE:

     The scope pattern shown in illustration is from the ECU side missing the HIGH side connection to the CAN bus harness. When checking the CAN bus is checked from the harness side a normal CAN bus scope pattern will appear.

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   • (-) Circuit Open 
     NOTE:

     The scope pattern shown in illustration is from the ECU side missing the LOW side connection to the CAN bus harness. When checking the CAN bus is checked from the harness side a normal CAN bus scope pattern will appear.

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   Did the Mopar Scope show the CAN-C bus waveform fault?

   • Use the appropriate SYSTEM WIRING DIAGRAMS as a guide to follow the path of the circuit(s) to isolate the fault further and then repair / replace as needed.
   • The condition that originally caused the concern may not be present at this time.
   • Continue to use the Mopar Scope and wiring diagrams as a guide to trace the circuits and look for any in-line connectors where the fault could occur intermittently by wiggling the wire harness and connectors.
   • Look for any chafed, pierced, pinched, or partially broken wires.
   • Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the related wire harness connectors.
   • Perform any Technical Service Bulletins (TSBs) that may apply.