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Home / DTC / B1A99 — Power reset The auxiliary and operational key entries are implausible

B1A99 — Power reset The auxiliary and operational key entries are implausible

Detailed page for trouble code B1A99.

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B1A99

LAND ROVER B — Body

Power reset The auxiliary and operational key entries are implausible

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

Causes

  • Loss of power or battery disconnection during key or module programming
  • Corrupted key memory in immobiliser / body control module (BCM)
  • Faulty or weak key fob battery or damaged transponder
  • CAN or LIN bus communication errors between security, BCM and engine modules
  • Incorrect or incomplete key programming or module software mismatch after update
  • Intermittent module power/ground or blown fuse

Symptoms

  • Immobiliser warning or security message on dash
  • Vehicle fails to start or cranks but will not run
  • Remote locking/unlocking or keyless entry intermittent or non-functional
  • Warning lamp relating to security/BCM
  • One or more keys no longer recognised while others may still work
  • Diagnostic trouble codes related to security, BCM or communication buses present

What to check

  • Record vehicle and key history (recent battery disconnects, module reflashes, key programming)
  • Check vehicle battery voltage and health (should be ~12.4–12.8 V at rest, >11 V cranking)
  • Check key fob battery state and test spare keys
  • Scan all modules for related DTCs (security/immobiliser, BCM, engine, CAN bus)
  • Check fuses, power and ground circuits to BCM/immobiliser module
  • Inspect CAN/LIN bus wiring and look for bus-off or excessive errors

Signal parameters

  • Battery voltage: nominal 12–14.5 V
  • Key fob battery voltage: typical 2.0–3.3 V depending on type
  • Transponder response: valid ID returned within expected timeout (typical
  • CAN bus idle voltage: ~2.5 V (dominant/recessive signals per protocol)
  • CAN error frame count / bus-off status: should be zero or within acceptable range
  • Immobiliser/BCM status flags: key_present, key_valid, security_locked

Diagnostic algorithm

  1. Retrieve and record all DTCs and freeze frame data from security, BCM and engine modules.
  2. Check vehicle and key battery voltages. Replace weak key fob battery and ensure vehicle battery is fully charged.
  3. Inspect fuses, power and ground connections for the BCM/immobiliser and repair any issues.
  4. Using OEM diagnostic tool, read key registry/list. Attempt to identify keys and note any mismatches or missing entries.
  5. Attempt to use a known-good (programmed) key to start vehicle. If spare key works, compare key IDs and registration status.
  6. If keys are not recognised, follow manufacturer procedure to re-learn/re-program keys with diagnostic tool. Ensure procedure completed without interruption.
  7. Check CAN/LIN communication during key validation (monitor messages and error counters). Repair wiring or module causing bus errors.
  8. If a recent module reflash or power loss occurred, verify correct software version and reapply correct flash/update if required.
  9. If problem persists after reprogramming and communications verified, consider immobiliser or BCM replacement per manufacturer guidance and reprogram keys to new module.
  10. Clear codes and retest all functions and start sequence. Document results and any modules reprogrammed/replaced.

Likely causes

  • Key memory corrupted by an unexpected power reset while keys were being registered
  • Faulty or discharged auxiliary (spare) key transponder battery causing inconsistent entry data
  • Module communication fault (CAN/LIN) preventing valid key ID validation
  • Software incompatibility or incomplete reflash of security/BCM module

Fault status

⚠️ Status
Power reset detected — auxiliary and operational key entries implausible. Security/immobiliser key data inconsistent; vehicle may not recognise one or more keys. Verify key registration, module communication and power/ground.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

B1A98 B1A9A U0100 U0073 U0121
266

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