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U0021 Network

Low Speed CAN Communication Bus (+) Low

CAN-High on the low-speed comfort bus is shorted to ground. Bus signaling is impaired or lost; affected comfort modules drop offline.

Affected components

  • Low speed can wiring

Common causes

  • High likelihood: CAN-High shorted to ground
  • Low likelihood: Gateway module routing CAN messages incorrectly
  • Low likelihood: CAN terminating resistor (120 Ω) drifted out of spec

Possible symptoms

  • Multiple warning lights may illuminate
  • Affected modules may go into limp mode or shut down
  • Specific functions inoperative depending on module
  • Diagnostic tools may show communication faults

Diagnostic notes

  • The malfunction indicator lamp may illuminate

Sources

Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.

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