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Home / DTC / U0047 — Vehicle Communication Bus C Performance

U0047 — Vehicle Communication Bus C Performance

Detailed page for trouble code U0047.

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U0047

MERCEDES-BENZ U — Network/User

Vehicle Communication Bus C Performance

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

Causes

  • Damaged or chafed CAN wiring (open, short to ground or battery, high resistance)
  • Faulty or corroded connector(s) on the Bus C harness
  • Failed control module driving or terminating the bus
  • Missing or incorrect termination resistor (open or shorted 120 Ω pair)
  • Low battery voltage, poor ground, or intermittent power to a module on Bus C
  • Electromagnetic interference (aftermarket equipment, high-current wiring routed near bus)

Symptoms

  • Multiple warning lamps or messages (communication errors, service lights)
  • Loss of function for modules on Bus C (e.g., instrument cluster, ADAS, comfort systems) or intermittent operation
  • Erratic behavior of systems that rely on Bus C data
  • Vehicle may enter limp / reduced-function mode if a critical module is affected
  • No obvious mechanical fault; many unrelated systems show faults simultaneously

What to check

  • Read all stored and pending U-codes and P-codes; note freeze frame and occurrence conditions
  • Check for other communication-related codes and identify which modules report errors
  • Verify battery voltage (12.4–12.8 V at rest; >13.5 V with engine running) and good chassis/body grounds
  • Visually inspect CAN wiring harness, connectors, and junctions along Bus C for damage or corrosion
  • Measure CAN termination resistance between CAN H and CAN L at two ends of the bus (≈120 Ω total across the bus)
  • Measure static voltages on CAN H and CAN L with key ON, engine OFF (recessive ~2.5 V each)

Signal parameters

  • CAN (recessive) idle voltage: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (range roughly 2.0–3.0 V)
  • CAN (dominant) voltages during transmission: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
  • Static resistance across bus (terminals at network ends): ≈ 120 Ω (with all modules connected)
  • Differential waveform: clean TTL-like waveform with correct bit timing for bus baud rate (commonly 500 kbps or 250 kbps on vehicle CAN networks)
  • Noise floor: minimal high-frequency noise; excess ringing or missing dominant/recessive transitions indicates problem

Diagnostic algorithm

  1. Capture freeze frame and full DTC list; record timestamps and repeating patterns.
  2. Recreate the fault conditions (key on, engine run, wiggling harness) to confirm reproducibility.
  3. Visually inspect connectors and wiring along Bus C; repair any damaged insulation, corrosion, or loose terminals.
  4. Verify battery and ground integrity; poor supply can cause modules to behave as bus faults.
  5. Measure CAN_H and CAN_L voltages with a DMM: confirm recessive voltages around 2.5 V each.
  6. Measure termination resistance across CAN_H and CAN_L at service connector: expect ≈120 Ω. If out of range, locate missing/shorted terminator or failed module.
  7. Use an oscilloscope to monitor differential CAN signal while exercising systems. Look for missing frames, stuck dominant, excessive noise, or incorrect bit timing.
  8. If oscilloscope shows a persistent fault, isolate by disconnecting modules or sections of the bus (one at a time) until the fault clears; the last disconnected item is likely faulty or connected to the fault location.
  9. Inspect and, if necessary, repair or replace the identified bad wiring, connector, terminator, or module. Replace modules only after confirming the module is the fault source.
  10. Clear codes, perform a full system re-scan, and road/test to ensure communication is restored and no further U0047 occurrences.
  11. If replacement module was required, verify correct software/configuration and perform any required coding or adaptation procedures.

Likely causes

  • Intermittent or high-resistance connection in CAN H/CAN L at a connector or splice
  • Open or shorted CAN wire due to chafing or water ingress
  • Failed module pulling the bus into a dominant state or going bus-off
  • Missing/failed termination resistor at one end of the bus

Fault status

⚠️ Status
CAN Bus C performance degraded or interrupted. Check wiring, termination, power/grounds, and modules on Bus C. Use oscilloscope and DTC list to isolate intermittent or dominant-state faults before replacing modules.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U0073 U0100 U0101 U0102 U0140 U0155
856

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