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Home / DTC / U0063 — Vehicle Communication Bus D (-) shorted to Bus (+)

U0063 — Vehicle Communication Bus D (-) shorted to Bus (+)

Detailed page for trouble code U0063.

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22,612specific
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Code

U0063

MERCEDES-BENZ U — Network/User

Vehicle Communication Bus D (-) shorted to Bus (+)

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

Causes

  • Wiring short between Bus D (-) and Bus D (+) due to chafing, pinched harness, or damaged insulation
  • Corroded or water-intruded connector or junction block connecting Bus D wires
  • Failed control module internally shorting a bus conductor to the opposite bus wire or to battery voltage
  • Improperly installed or faulty aftermarket device tied into the bus
  • Incorrect wiring or repair (swapped or bridged conductors, poor splice/repair)
  • Damaged termination resistor or incorrect termination (causing abnormal voltages)

Symptoms

  • One or more control modules not responding or showing communication errors
  • Illumination of MIL or multiple warning lamps (ABS, traction, airbags, etc.)
  • Loss of features tied to Bus D (e.g., instrument cluster, gateway, driver assistance)
  • Erratic or intermittent module behavior, stored communication-related DTCs
  • No bus traffic shown on scan tool for the affected network

What to check

  • Use a capable scan tool to read all U-codes and note which modules report loss of communication
  • Visually inspect Bus D wiring routes, connectors, and junction boxes for damage, corrosion, or water
  • Measure DC voltage of each bus conductor to chassis and to each other with ignition ON (key on, engine off)
  • Check for low resistance/short between Bus D (-) and Bus D (+) with ignition OFF
  • Disconnect suspect modules or branch connectors one at a time to isolate the short
  • Inspect and verify termination resistors at bus ends and continuity to ground for shields if present

Signal parameters

  • Expected (recessive) voltage: Bus D (+) ≈ 2.5 V, Bus D (–) ≈ 2.5 V (each to chassis), differential ≈ 0 V
  • Expected (dominant) voltages during traffic: Bus D (+) ≈ 3.5 V, Bus D (–) ≈ 1.5 V (differential ≈ 2.0 V)
  • Short condition: one conductor pulled toward higher battery voltage or the two conductors nearly equal to battery or ground
  • Resistance between Bus D (+) and Bus D (–) should be high (except normal termination ~60 ohms across both lines)

Diagnostic algorithm

  1. Record all active and historic codes and freeze-frame data with a scan tool; note modules offline.
  2. Clear codes and perform an ignition cycle to confirm repeatability of U0063.
  3. Visually inspect entire Bus D harness path, connectors, and junction blocks for damage or corrosion.
  4. With ignition OFF, measure continuity/resistance between Bus D (+) and Bus D (–) to check for a direct short.
  5. With ignition ON, carefully measure DC voltage on each bus conductor to chassis and between each other. Look for a conductor held at battery voltage.
  6. Isolate the circuit by disconnecting connectors or modules along the bus in a logical order to locate the segment causing the short (start at easily accessible modules/junctions).
  7. If isolating by disconnection is inconclusive, use a current-limited bench supply or fused jumper and amp meter to locate excessive current draw on the bus wiring (exercise caution to avoid damage).
  8. Inspect and test termination resistors at both physical ends of Bus D for correct resistance (~120 ohms total across the two wires on many systems; verify OEM spec).
  9. Repair or replace the damaged wiring, connector, or failed control module as identified. Use OEM repair methods and ensure proper insulation, routing, and sealing.
  10. After repair, reconnect modules, clear codes, perform full system scan, and road/test to confirm communication is restored and no new codes reappear.

Likely causes

  • Physical damage to the Bus D harness at a location where it is routed near chassis or sharp edges
  • Connector pin corrosion or broken pin making intermittent contact leading to a short under movement
  • A single control module with internal failure pulling one conductor toward battery voltage
  • Water ingress at a known connector/junction near the front or rear modules

Fault status

⚠️ Status
Bus D (-) conductor is electrically shorted to Bus D (+). Network traffic on Bus D is impaired or absent; affected modules may lose communication or function.
🔴 Repair difficulty: Hard
⏱️ Diagnostic time: 2-6 hours

Similar codes

U0073 U0100 U0121 U0401 U0060
856

Browse 856 MERCEDES-BENZ manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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