Toggle Side Panel

Shopping Cart

No products in the basket.

Shopping Cart

No products in the basket.

Close search
Home / DTC / B1A21 — Left Front Door Module: Invalid Data Received

B1A21 — Left Front Door Module: Invalid Data Received

Detailed page for trouble code B1A21.

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

B1A21

LAND ROVER B — Body

Left Front Door Module: Invalid Data Received

Brand: LAND ROVER
Type: B — Body
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Corroded, loose or damaged connector at the left front door module
  • Low or intermittent module supply voltage or poor ground
  • CAN/LIN bus wiring fault, short, open, or poor termination
  • Water intrusion or physical damage to the door module
  • Module software mismatch, corrupted flash memory or failed internal electronics
  • Aftermarket devices or recent repairs that altered wiring or module coding

Symptoms

  • One or more door functions intermittent or inoperative (locks, window, mirror, courtesy light)
  • Door ajar or lock status incorrect on dash or central locking operates erratically
  • Related body systems report communication warnings or fail to respond to commands
  • CEL or other network communication fault indicators may be present
  • Doors may operate normally sometimes and fail at other times (intermittent)

What to check

  • Read all stored and pending DTCs from all modules — note any U-codes or other B-codes
  • Check freeze frame and occurrence count for B1A21; clear code and see if it returns immediately or after specific events
  • Use a diagnostic tool to view live data from LFDM (door status, message frequency, voltages)
  • Visually inspect left front door wiring harness, pin connectors and rubber boot for chafing, corrosion, or water entry
  • Measure supply voltage at the LFDM (key on) and check ground resistance to chassis
  • Inspect CAN/LIN wiring and connectors for corrosion, bent pins or poor seating

Signal parameters

  • LFDM supply voltage ~11–14V (Key ON)
  • Module ground continuity
  • Door open/close status (0/1), lock status (locked/unlocked) — stable, not random
  • Window position/command values 0–100% and matching switch inputs
  • CAN message ID from LFDM present and with consistent frequency (milliseconds interval)
  • CAN bus voltage idle ~2.5V on each CAN_H/CAN_L (differential ~2V) and proper termination (approx. 60 ohms across bus)

Diagnostic algorithm

  1. Record full module list and all codes from vehicle, note any U-codes (network) and related B-codes. Clear codes and attempt to re-create fault conditions.
  2. With a scan tool, monitor LFDM live data while operating door functions (lock/unlock, window up/down, mirror) and watch for invalid or missing values or message dropouts.
  3. Perform a visual inspection of the left front door harness, connector, and hinge boot for damage, corrosion or water ingress. Repair any visible damage.
  4. Measure supply and ground at the LFDM connector with key ON: confirm battery voltage and good ground. Repair any high-resistance connections.
  5. Probe CAN bus at or near the LFDM: verify CAN_H/CAN_L idle voltages, presence of LFDM CAN frames and correct frequency. Use oscilloscope/diagnostic tool to look for noise, reflections or corrupted frames.
  6. Perform continuity/resistance checks from LFDM connector pins to the associated junction/BCM pins to identify opens/shorts, paying attention to harness chafe at the door hinge.
  7. If wiring and bus are good, verify module software/coding and compare part number to OEM specification. Reflash/update software or correct coding if required.
  8. As a final step, substitute a known-good LFDM (or bench test module) where possible to confirm module fault before replacement. After repair, clear codes and perform full function test and road test to verify fault does not return.

Likely causes

  • Open or high-resistance ground/supply to LFDM
  • Intermittent CAN bus communication (missing/garbled messages)
  • Corroded door harness at hinge/boot causing intermittent signals
  • Internal LFDM failure (processor or memory corruption)
  • Incorrect module coding or out-of-date software after replacement/repair

Fault status

⚠️ Status
Invalid/out-of-range or corrupted data received from Left Front Door Module (LFDM). Communication or internal module data integrity fault detected.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0 - 2.5 hours
320

Browse 320 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

LAND ROVER

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 .