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Home / DTC / U0050 — Vehicle Communication Bus C (+) high

U0050 — Vehicle Communication Bus C (+) high

Detailed page for trouble code U0050.

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Code

U0050

MERCEDES-BENZ U — Network/User

Vehicle Communication Bus C (+) high

Brand: MERCEDES-BENZ
Type: U — Network/User
AI status
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Completed 100%
Page language: EN

Causes

  • Short or partial short of Bus C (+) to battery voltage
  • Wiring chafing, pin corrosion, or connector damage on Bus C
  • Failed CAN/LIN transceiver or control module driving Bus C
  • Incorrect or missing termination resistor(s)
  • Aftermarket device or improper module retrofit tied into Bus C
  • Water ingress or contamination in junctions or modules

Symptoms

  • Illumination of communication or multiple warning lamps
  • Loss of communication with one or more modules on Bus C
  • Intermittent or permanent loss of functions controlled by affected modules
  • Modules entering bus-off or failing to respond to diagnostic tool
  • Vehicle may enter limp mode or have drivability faults if key modules are affected

What to check

  • Read and record all stored U-codes and related module fault codes
  • Check battery voltage and main fuses; ensure stable supply voltage
  • Visually inspect harnesses, connectors and junction boxes for corrosion, water, or damage on Bus C lines
  • Use a scan tool to observe which modules are online and whether any modules report bus-off
  • Measure DC voltage on Bus C (+) relative to ground and relative to Bus C (-) with ignition on
  • With ignition off, measure resistance between Bus C (+) and Bus C (-) across termination; expected ~60 ohms (typical CAN) — confirm manufacturer spec

Signal parameters

  • Static voltage on Bus C (+) to ground with ignition ON and bus idle (compare to manufacturer spec)
  • Differential voltage between Bus C (+) and Bus C (-) during idle and active switching
  • Termination resistance across Bus C (+) and Bus C (-) with power OFF (typical CAN ≈ 60 ohms total)
  • Short-to-battery or short-to-ground resistance measurements from Bus C (+)
  • Oscilloscope waveform showing proper recessive/dominant transitions on Bus C when modules transmit

Diagnostic algorithm

  1. Capture and save all diagnostic trouble codes and freeze frame data from all control modules. Note which modules show 'no communication' or 'bus-off'.
  2. Verify vehicle battery state-of-charge and main power/ground distribution; correct low battery conditions before further testing.
  3. Visually inspect all connectors, junction boxes and harness routing for damage or contamination on Bus C wiring. Repair obvious damage.
  4. Using a scan tool, determine which modules are present or missing on Bus C. Identify the last-known good module or location of recent service/aftermarket installs.
  5. With ignition ON, measure voltage at the Bus C (+) conductor at a convenient connector. If voltage is higher than spec, backprobe harness toward modules to localize the high-voltage source.
  6. With ignition OFF, measure resistance between Bus C (+) and battery positive and between Bus C (+) and ground to identify a short path. Isolate sections by disconnecting connectors or modules and re-measuring to find the faulty section.
  7. Check termination: measure resistance across Bus C (+) and Bus C (-) at each segment with power off. If termination is missing or abnormal, inspect gateway/terminator resistors and replace as required.
  8. If the suspect module is isolated, swap or bench-test the module’s transceiver per manufacturer procedure or substitute a known-good module where applicable.
  9. Repair any damaged wiring, connectors, or termination components. Clean corroded terminals and ensure proper sealing against moisture.
  10. Clear codes and verify repair by confirming normal bus voltages, restoring all modules to online status, and road-testing to ensure no recurrence.

Likely causes

  • Short to battery on Bus C (+) (most common)
  • Faulty transceiver in a module connected to Bus C
  • Damaged connector or harness near gateway or junction box
  • Missing/incorrect termination or harness splice

Fault status

⚠️ Status
Vehicle Communication Bus C (+) high — the positive conductor of Bus C is above the specified voltage threshold. This indicates an electrical fault (short to battery, failed transceiver, incorrect termination, or wiring fault) that is preventing normal network communication.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 2.0-4.0 hours

Similar codes

U0051 U0040 U0073 U0100 U0121
856

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