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Home / DTC / U0073 — Control Module Communications Bus Off

U0073 — Control Module Communications Bus Off

Detailed page for trouble code U0073.

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Code

U0073

MERCEDES-BENZ U — Network/User

Control Module Communications Bus Off

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

Causes

  • Short to battery or ground on CAN high or CAN low wiring
  • Open or intermittent wiring/connectors on the data bus
  • Failed module transceiver driving the bus into error state
  • Missing or incorrect termination (open/shorted 60 Ω across CAN H/L)
  • Low system voltage or poor battery/ground connections
  • Corrosion or water intrusion in harness/connectors

Symptoms

  • Loss of communication with one or more modules (modules unavailable on scan tool)
  • Multiple diagnostic trouble codes related to communication (U-codes)
  • Intermittent or complete loss of vehicle functions controlled by affected modules
  • Possible warning lights or malfunction indicator lamps on dash
  • No network traffic visible on CAN bus with scan tool when bus-off is active

What to check

  • Connect a professional scan tool and read all stored and pending U-codes and freeze-frame data
  • Identify which module(s) report(s) bus-off and which networks are affected (CAN high-speed, medium-speed, CAN FD, LIN gateway)
  • Visually inspect CAN wiring, connectors, module grounds and battery connections for damage or corrosion
  • Measure battery voltage and charge state; ensure good battery and ground connections
  • Check termination resistance across CAN H and CAN L (approximately 60 Ω total with ignition off)
  • Monitor CAN H and CAN L signals with a scope or capable scan tool to observe idle voltages and error frames

Signal parameters

  • CAN_H idle voltage ≈ 2.5 V (recessive), CAN_L idle ≈ 2.5 V; dominant state drives CAN_H ≈ 3.5 V and CAN_L ≈ 1.5 V (values vary by manufacturer)
  • Differential voltage (CAN_H − CAN_L) ≈ 2.0 V when dominant
  • Termination resistance CAN_H to CAN_L ≈ 60 Ω (two 120 Ω in parallel)
  • Bus-off flag set in the offending module’s transceiver status
  • Error counter values and number of error frames visible with a capable scope/diagnostic tool

Diagnostic algorithm

  1. Use a scan tool to record all active/stored codes and identify which module reports U0073 and which network is affected.
  2. Verify battery voltage and engine off/on states. Recharge or replace weak battery and clean battery terminals/grounds before proceeding.
  3. Visually inspect connectors, wiring harnesses, and module grounds for damage, corrosion, or water intrusion near the module that reported bus-off.
  4. With ignition off, measure termination resistance across CAN_H and CAN_L at a convenient connector; expect ~60 Ω. If open or abnormal, trace wiring for open/short.
  5. With a lab scope or CAN bus monitor, observe CAN_H and CAN_L signals with ignition on and engine off. Look for idle voltages, excessive noise, stuck dominant, missing recessive, or continual error frames.
  6. If scope shows a short to battery or ground on a bus line, isolate by disconnecting connectors or modules in sections until the short clears or the bus returns to normal.
  7. If disconnecting a specific module restores normal bus operation, suspect that module’s transceiver or internal fault. Verify wiring to that module and check for aftermarket devices or splices.
  8. Repair any wiring faults, replace damaged connectors, and correct termination. After repairs, clear codes and confirm stable bus traffic and absence of U0073.
  9. If a module is suspected, replace or repair the module only after confirming the bus and wiring are correct. Reprogram or code replacement module per manufacturer procedures.
  10. If intermittent faults remain, perform wiggle tests with scope/monitor and inspect for heat/moisture-correlated failures; consider harness replacement in high-damage areas.

Likely causes

  • Faulty control module transceiver (most likely the module reporting the bus-off)
  • Damaged/shorted CAN H or CAN L wiring near the module
  • Bad ground or low battery voltage causing bus instability
  • Failed termination resistor or harness splice shorting to battery/ground

Fault status

⚠️ Status
Control module reports the communications bus is "bus off" — the module stopped transmitting because it detected excessive errors on the network. Communication with other modules may be lost until the fault is corrected.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-4 hours

Similar codes

U0077 U0100 U0101 U0121 U0140
856

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