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Home / DTC / B1D20 — Body Control Module — Internal Fault

B1D20 — Body Control Module — Internal Fault

Detailed page for trouble code B1D20.

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B1D20

LAND ROVER B — Body

Body Control Module — Internal Fault

Brand: LAND ROVER
Type: B — Body
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Page language: EN

Causes

  • Faulty BCM hardware (internal electronics or circuit board)
  • Corrupt or failed BCM software/firmware
  • Intermittent or lost power/ground to the BCM (battery, fuses, ignition feed)
  • Water ingress, corrosion or physical damage to BCM or connector
  • CAN/LIN bus electrical fault causing module fault reporting
  • Aftermarket device or improper retrofit causing interference or short

Symptoms

  • Malfunctioning interior/exterior lighting and convenience features (locks, windows, wipers)
  • Intermittent or total loss of some body electrical functions
  • Multiple communication-related DTCs present (CAN/LIN comm errors)
  • Vehicle may display warning lights or reduced feature functionality
  • BCM does not respond to diagnostic tool or responds intermittently

What to check

  • Read and record all stored and pending DTCs and freeze-frame data from BCM and other modules
  • Verify battery state of charge and charging system health before diagnosing
  • Visually inspect BCM, mounting area and connectors for corrosion, moisture, damage or water ingress
  • Check fuses and relay(s) related to BCM power/ignition feeds
  • Verify connector pin retention, corrosion and proper wiring harness seating at BCM
  • Scan CAN/LIN network for related communication codes and verify bus activity with a scan tool or oscilloscope

Signal parameters

  • Battery supply to BCM: nominal ~12–14.6 V with engine running; present at constant and switched power pins
  • Ignition-switched feed present when key in RUN/ON
  • Grounds: low-resistance connection between BCM ground pins and chassis
  • CAN bus: active bus traffic present; module should respond to diagnostic requests (CAN High/Low differential activity observable with scope or bus monitor)
  • LIN or local serial lines (if used): expected idle states and responsiveness to gateway/host module requests
  • Module diagnostic response: should acknowledge UDS/DoIP/Diag protocol sessions when healthy

Diagnostic algorithm

  1. Record all module DTCs and freeze-frame data from BCM and related modules (gateway, ABS, ECM). Do not erase initially
  2. Verify vehicle battery voltage and charge as low voltage can create spurious internal faults
  3. Perform thorough visual inspection of BCM and connector for moisture, corrosion, broken pins or heat damage; repair as necessary
  4. Check related fuses/relays and measure power and ground at the BCM harness with the connector connected if possible
  5. Use a manufacturer-level diagnostic tool to attempt communication with the BCM; note if module is present, responds intermittently, or is absent from the bus
  6. If communication fails, scan the CAN/LIN network for bus-off conditions or other modules reporting communication loss (codes like U0100, U0073 may co-exist)
  7. Backprobe power and ground while exercising ignition to confirm stable supplies under load; wiggle harness to replicate intermittent faults
  8. If CAN bus activity is abnormal, inspect wiring and nearby modules for short/loads; use oscilloscope or bus monitor to capture signals
  9. Check for available BCM software/firmware updates or service bulletins; attempt software reflash/reprogram only with proper OEM tool and procedures
  10. If diagnostics and bench tests indicate internal BCM failure (no comms, self-test fail, corrupted firmware) and wiring/power/ground and bus are confirmed good, replace BCM per manufacturer procedure and perform required module programming and immobilizer/key matching
  11. After repair or module replacement, clear codes and perform full system function tests and a road test to confirm no return of fault

Likely causes

  • Failed internal components on the BCM circuit board
  • Blown fuse or poor ignition/constant power supply to BCM
  • Damaged or corroded multipin connector at the BCM
  • CAN bus wiring fault or bus shorting to ground/power
  • Incomplete or failed software update/flash
  • Moisture intrusion causing intermittent faults

Fault status

⚠️ Status
BCM internal fault detected (self-test failure). The module recorded an internal error and may be non-responsive or producing communication faults. Further diagnosis required to confirm whether fault is internal or caused by external power/communication issues.
🔴 Repair difficulty: Hard
⏱️ Diagnostic time: 2.0 - 5.0 hours

Similar codes

U0100 U0073 U1000 P0606 P0603
413

Browse 413 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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