Toggle Side Panel

Shopping Cart

No products in the basket.

Shopping Cart

No products in the basket.

Close search
Home / DTC / U0041 — Vehicle Communication Bus B (+) high

U0041 — Vehicle Communication Bus B (+) high

Detailed page for trouble code U0041.

34,405codes
59brands
11,914generic
22,491specific
All codes P-codes (Powertrain) B-codes (Body) C-codes (Chassis) U-codes (Network/User) Tesla Alerts
Reset
Code

U0041

MERCEDES-BENZ U — Network/User

Vehicle Communication Bus B (+) high

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

Causes

  • Short to battery or other power source on CANH (Bus B)
  • Damaged wiring or pinched cable on CANH or CANL
  • Faulty control module driving the Bus B high
  • Poor or corroded connector/ground affecting the bus
  • Aftermarket accessory or module tied into the CAN network incorrectly
  • Failed or missing termination resistor(s) on Bus B

Symptoms

  • One or more modules on Bus B not responding or showing communications faults
  • Multiple network-related fault codes
  • Warning lamps related to affected systems (e.g., ABS, instrument cluster, transmission)
  • Loss of functions controlled by Bus B modules
  • Intermittent or constant communication errors while driving or at startup

What to check

  • Visual inspection of CAN wiring harnesses, connectors, and module pins for damage, corrosion, or recent repairs
  • Check for aftermarket devices or modifications connected to the network and remove temporarily
  • Measure voltage between CANH-B and battery negative with key on, engine off
  • Measure resistance between CANH-B and CANL-B (termination) with ignition off
  • Use an oscilloscope to view CANH/CANL waveforms on Bus B under normal and fault conditions
  • Disconnect individual Bus B modules (one at a time) to isolate the source of the high voltage

Signal parameters

  • Recessive state: CANH-B ≈ 2.5 V, CANL-B ≈ 2.5 V (both near mid-rail)
  • Dominant state: CANH-B typically rises ≈ 3.5–3.9 V, CANL-B drops ≈ 1.5–1.1 V (differential ≈ 2 V)
  • Bus high fault: CANH-B sustained above ~3.6–4.0 V or close to battery voltage indicates a possible short to +12 V
  • Termination: ~60 Ω between CANH-B and CANL-B (two 120 Ω resistors in parallel) with ignition off
  • No communication: waveform absent or stuck at a DC voltage on CANH-B or CANL-B

Diagnostic algorithm

  1. Record all related network and module fault codes and freeze frame data before clearing.
  2. Perform a careful visual inspection of Bus B wiring from modules to central gateway for chafing, pin damage, heat or water ingress.
  3. Remove aftermarket devices or recently added wiring from the network; see if code clears.
  4. With ignition ON (engine off), measure DC voltage on CANH-B to chassis ground; compare to expected idle ~2.5 V. Note any sustained high voltage.
  5. Measure resistance between CANH-B and CANL-B with ignition OFF; expected around 60 Ω. If open or low, investigate termination resistors and bus continuity.
  6. Connect an oscilloscope to CANH-B and CANL-B and observe waveforms while attempting to communicate; look for DC offset, stuck high, or abnormal amplitude.
  7. If bus appears high, disconnect modules on Bus B one at a time (while monitoring voltage/waveform) to locate the module that, when disconnected, returns the bus to normal.
  8. If a specific module is isolated as the cause, verify its power/ground and connector pins. Replace or repair wiring or module only after confirming fault source.
  9. After repair, clear codes and verify normal CAN waveforms, termination resistance, and restoration of communications across Bus B; road test to confirm no reoccurrence.
  10. If inability to isolate or repair, refer to manufacturer wiring diagrams and contact technical support; consider gateway or body control module tests per factory procedures.

Likely causes

  • Short to +12V on CANH conductor (pin damage, chafing, connector contamination)
  • Defective ECU on Bus B forcing CANH high
  • Incorrect aftermarket module or jumper creating a high voltage condition
  • Open or incorrect termination (missing 120Ω resistors / incorrect parallel resistance)
  • Intermittent wiring short caused by movement or water ingress

Fault status

⚠️ Status
CAN Bus B positive line voltage above expected range (CANH-B high). Possible short to power, faulty module, or wiring/termination fault causing loss of network communication.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.5 hours

Similar codes

U0040 U0073 U0100 U0101 U0131
856

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

MERCEDES-BENZ

Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email

Report

Harassment or bullying behavior
Contains mature or sensitive content
Contains misleading or false information
Contains abusive or derogatory content
Contains spam, fake content or potential malware

Block Member?

Please confirm you want to block this member.

You will no longer be able to:

  • See blocked member's posts
  • Mention this member in posts
  • Invite this member to groups
  • Message this member
  • Add this member as a connection

Please note: This action will also remove this member from your connections and send a report to the site admin. Please allow a few minutes for this process to complete.

Report

You have already reported this .