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Home / DTC / B1C91 — Body Control Module — Sensor Signal Fault

B1C91 — Body Control Module — Sensor Signal Fault

Detailed page for trouble code B1C91.

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B1C91

LAND ROVER B — Body

Body Control Module — Sensor Signal Fault

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

Causes

  • Damaged or shorted sensor wiring or connector
  • Corroded, loose or water-damaged connector at the sensor or BCM
  • Failed sensor (open, short, out-of-range output)
  • Poor BCM power or ground connection
  • Intermittent contact from vibration or chafing
  • Faulty BCM internal input circuitry or firmware error

Symptoms

  • Stored B1C91 (often accompanied by related BCM or network codes)
  • One or more body functions inoperative or intermittent (lighting, locks, wipers, HVAC inputs, etc.)
  • Instrument cluster warnings or service messages
  • Vehicle behaves normally at times and incorrectly at others (intermittent)
  • Related systems reporting incorrect sensor values in live data

What to check

  • Read all stored and pending codes from all modules with an OEM-capable scanner; note freeze-frame and related codes
  • Check battery voltage and BCM supply/ground integrity
  • Visually inspect sensor and BCM connectors for corrosion, bent pins, water intrusion, or damage
  • Wiggle test wiring and connectors while monitoring live data for changes
  • Inspect wiring harness routing for chafing, repairs, or pinched sections
  • Check CAN bus health and look for related U-codes if the sensor data is networked

Signal parameters

  • Typical sensor voltage range: 0–5.0 V (some sensors use 0.5–4.5 V)
  • Thermistor temperature sensors: resistance varies with temperature (consult OEM table)
  • Pulse/frequency sensors: frequency or duty cycle expected in service manual
  • CAN bus nominal voltages: ~2.5 V on each bus wire (differential signaling); check CAN_H/CAN_L levels and termination
  • Continuity: expected low resistance between sensor and BCM signal pin (< a few ohms for short harness runs), no shorts to battery or ground

Diagnostic algorithm

  1. Retrieve all DTCs from BCM and other modules and record freeze-frame/conditions.
  2. Check battery voltage and charging system; low voltage can cause false faults. Recharge or stabilize battery if low.
  3. Inspect sensor and BCM connectors for corrosion, bent pins, water damage, or poor seating; repair as needed.
  4. With ignition on, monitor the suspect sensor signal using an OEM scan tool (live data) to see if values are present and within expected range.
  5. If available, use an oscilloscope to observe sensor waveform or voltage under known conditions; compare to expected specification.
  6. Perform a wiggle test on wiring harness while monitoring live data; look for intermittent changes or dropouts.
  7. Check continuity and insulation between sensor signal, power, and ground to the BCM; repair any opens/shorts.
  8. Verify BCM supply and ground circuits at the module connector (voltage and resistance). Repair poor grounds or power feeds.
  9. If sensor is accessible, swap with a known-good sensor or bench-test the sensor per OEM procedure.
  10. If wiring and sensor verify OK, check for related CAN/network errors and re-flash or update BCM software per manufacturer bulletin.
  11. If all tests pass and fault persists, consider BCM replacement only after confirming all inputs, power, and grounds are correct.
  12. Clear codes and perform test drive to confirm the fault does not return and related function is restored.

Likely causes

  • Connector or wiring problem between sensor and BCM (most common)
  • Failed sensor producing no or erratic signal
  • Poor ground or low supply voltage to sensor/BCM
  • BCM hardware fault or corrupted software (less common)

Fault status

⚠️ Status
Body Control Module has detected an invalid, missing or out-of-range sensor signal input. Functionality related to that sensor or networked data may be degraded or disabled.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

B1C90 B1C92 B1C93 U0100 U0121
413

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