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Home / DTC / B1850 — Electric seat adjustment front right: CAN communication interrupted with DCM

B1850 — Electric seat adjustment front right: CAN communication interrupted with DCM

Detailed page for trouble code B1850.

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Code

B1850

MERCEDES-BENZ B — Body

Electric seat adjustment front right: CAN communication interrupted with DCM

Brand: MERCEDES-BENZ
Type: B — Body
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or short in CAN wiring between seat module and DCM
  • Corroded/damaged connector or poor pin contact at seat or DCM
  • Faulty front-right seat control module (seat control unit)
  • Faulty Door/Driver Control Module (DCM) or internal CAN transceiver fault
  • Missing or incorrect bus termination (open/shorted termination resistor)
  • Low battery voltage or unstable supply to the seat module/DCM

Symptoms

  • Front-right seat adjustment inoperative or intermittent
  • Seat memory or heating functions for that seat not working
  • Driver information display/warning message about seat malfunction
  • Other body modules reporting communication faults or related DTCs
  • DTC returns immediately after clearing or appears intermittently with seat movement

What to check

  • Use a capable scan tool to read freeze frames, timestamps and all related network U-codes (lost communication)
  • Check for related U- and B-codes on other modules to determine scope
  • Visually inspect connectors at the seat base, under trim and at the DCM for corrosion, loose pins, broken wires or water damage
  • Check fuses and power/ground supply to the seat control module and DCM
  • With ignition on, observe CAN bus traffic on a scan tool — verify the seat module node appears and sends frames
  • Measure CAN_H and CAN_L voltages at the seat connector with key ON: idle ~2.5 V each relative to ground and differential across H-L ~0 V idle, verify termination resistance ≈60 Ω across H-L with ignition off

Signal parameters

  • CAN bus idle: CAN_H ≈2.5 V, CAN_L ≈2.5 V (each to ground); differential idle ~0 V
  • When active: CAN_H pulses toward ~3.5 V and CAN_L toward ~1.5 V (differential ≈2 V)
  • Termination resistance: approx. 60 Ω across CAN_H–CAN_L (two 120 Ω in parallel)
  • Expected seat module frames visible on bus when scanning (node ID/frames will vary by model)
  • Battery voltage present at seat module power pin(s) within normal range (typically 12–14.5 V with engine running)

Diagnostic algorithm

  1. Read all stored DTCs on body and gateway modules; record freeze frame and related U-codes
  2. Clear codes, attempt to re-create fault; note whether immediate or intermittent
  3. Inspect and reseat connectors at the front-right seat module and at the DCM; look for bent pins, corrosion or water ingress
  4. Check battery voltage and engine off/on to verify stable supply to seat module and DCM
  5. Using a scan tool, monitor CAN traffic and verify whether seat module is transmitting — if absent, confirm at module connector with a lab scope or meter (observe idle voltages and differential)
  6. Measure continuity and resistance of CAN_H and CAN_L between seat module and DCM; check for short to ground or 12 V
  7. Measure termination resistance at two points on the bus to confirm ~60 Ω; isolate sections if termination incorrect
  8. If wiring and power/ground good but no communication, replace or bench-test the seat control module per manufacturer guidance
  9. If multiple modules report loss of communication, investigate gateway or central communication module and consult wiring diagrams
  10. After repairs, clear codes and perform full function test including seat movement through full travel and verify no return of DTC; follow any manufacturer software update or coding procedures
  11. Always follow safety instructions in the service manual when working around seat wiring and restraint components (airbags, pretensioners); disconnect battery and wait as specified before removing connectors if required)

Likely causes

  • Damaged or corroded connector at seat (common with seat movement)
  • Broken CAN wire in harness routed through seat base or door hinge area
  • Faulty seat control module CAN transceiver
  • Intermittent ground or 12V supply to seat module causing loss of CAN participation

Fault status

⚠️ Status
Electric seat adjustment front right: CAN communication interrupted with DCM (lost CAN link between seat control module and Door/Driver Control Module).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.5 hours

Similar codes

U0073 U0100 U0155 B1851
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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