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Home >> Jeep >> 2005 >> Wrangler Rubicon, Standard >> Repair and Diagnosis >> External Pages >> Different car >> Section 603 (Audio System & Video System - Electrical Diagnostics) >> Audio/Video Systems - Electrical Diagnosis >> DTC Troubleshooting >> U0020-Can B Bus Off Performance >> Diagnostic Test

Diagnostic Test

WARNING: This page is about a different car, the 2005 Jeep Grand Cherokee. However, it is still accessible from the selected car via links, so may be relevant.
  1. 1)  TEST FOR INTERMITTENT CONDITION 
    Fig 1: Scan Tool - Starscan
    GC0028920Courtesy of DAIMLERCHRYSLER CORP.

    Turn the ignition on.

    With the scan tool, record and erase DTCs

    Cycle the ignition from on to off 3 times.

    Turn the ignition on.

    With the scan tool, read DTCs.

    Does the scan tool display U0020-CAN B BUS OFF PERFORMANCE? 

    Yes 

    1. Go To step  2).

    No 

    1. The conditions that caused this code to set are not present at this time. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors.
    2. Perform BODY VERIFICATION TEST - VER 1 .
  2. 2)  CHECK FRONT CONTROL MODULE DTCs 
    Fig 2: Scan Tool - Starscan
    GC0028920Courtesy of DAIMLERCHRYSLER CORP.

    With the scan tool, read Front Control Module DTCs

    Does the scan tool display any CAN B BUS DTCs - ACTIVE? 

    Yes 

    1. Refer to the symptom list for problems related to Communication in the ELECTRONIC CONTROL MODULES - ELECTRICAL DIAGNOSTICS .

    No 

    1. Go to step  3).
  3. 3)  CAN B BUS (+) CIRCUIT OPEN 
    Fig 3: Can B Bus (+) Circuit Open
    GC0028922Courtesy of DAIMLERCHRYSLER CORP.

    Turn the ignition off.

    Disconnect the Amplifier harness connector.

    Disconnect the Front Control Module C1 harness connector.

    Measure the resistance of the (D55) Can B Bus (+) circuit between the Front Control Module C1 harness connector and the Amplifier harness connector.

    Is the resistance below 2.0 ohms? 

    Yes 

    1. Go To step  4).
    2. Perform BODY VERIFICATION TEST - VER 1 .

    No 

    1. Repair the Can B Bus (+) circuit for an open.
    2. Perform BODY VERIFICATION TEST - VER 1 .
  4. 4)  CAN B BUS (-) CIRCUIT OPEN 
    Fig 4: Can B Bus (-) Circuit Open
    GC0028923Courtesy of DAIMLERCHRYSLER CORP.

    Measure the resistance of the (D54) Can B Bus (-) circuit between the Front Control Module C1 harness connector and the Amplifier harness connector.

    Is the resistance below 2.0 ohms? 

    Yes 

    1. Replace the Amplifier in accordance with the service information.
    2. Perform BODY VERIFICATION TEST - VER 1 .

    No 

    1. Repair the Can B Bus (-) circuit for an open.
    2. Perform BODY VERIFICATION TEST - VER 1 .
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