Code
P1517
CITROEN
P — Powertrain
Engine immobiliser function
AI status
Completed
Completed
100%
Causes
- Transponder key not recognised by immobiliser
- Faulty or weak key/battery in remote key
- Antenna (coil) around ignition barrel damaged or disconnected
- Body control module (BSI) / immobiliser ECU software or hardware fault
- Loss of CAN/serial communication between immobiliser module and engine ECU
- Blown fuse, poor power/ground to immobiliser or ECU
Symptoms
- Engine will not start (cranks but no start) or no crank depending on vehicle configuration
- Security/immobiliser warning lamp illuminated or flashing on instrument cluster
- Intermittent no‑start that sometimes clears with spare key
- Starter disabled or fuel/ignition cut when fault present
- No key recognition message displayed on dash
What to check
- Use a capable diagnostic tool to read stored DTCs from engine ECU, BSI and immobiliser module
- Try a known-good/spare key and note behaviour
- Check key battery voltage and replace if low
- Inspect fuses and supply/ground at immobiliser and engine ECU
- Visually inspect antenna coil and wiring at ignition barrel for damage or corrosion
- Check CAN bus health and for related communication errors (U0100 style codes)
Signal parameters
- Transponder/key ID received by immobiliser (logical presence/ID)
- Antenna coil presence/pulse when key inserted or near reader
- Key battery voltage (for passive/remote authentication features)
- Immobiliser status message on CAN (engine enable/disable flag)
- Engine ECU authorization response (unlock/fuel enable)
Diagnostic algorithm
- Read and record all DTCs from engine ECU, BSI and immobiliser module; note freeze frame or related time stamps.
- Confirm symptoms: does vehicle crank? Does behaviour change with spare key? Attempt key in different ignition positions if applicable.
- Check key battery and, if remote/keyless, test proximity recognition; replace battery if low and retest.
- Inspect fuses, power and ground circuits to immobiliser/BSI and engine ECU; repair any poor connections.
- Inspect antenna ring and wiring at the ignition barrel or key reader for damage; measure for continuity and expected signal when key is presented (per workshop manual).
- Use a diagnostic tool to watch immobiliser and CAN messages while attempting start. Look for 'no response' or 'not authorised' messages between modules.
- If communication faults present, trace and repair CAN wiring/connectors between BSI, instrument cluster, immobiliser and engine ECU.
- If key not recognised but wiring and power OK, attempt reprogram/relearn of key(s) following manufacturer procedure. Verify VIN and module programming status.
- After repairs or reprogramming, clear codes and perform several start cycles to confirm fault does not return. If recurring, capture diagnostic logs and consider immobiliser or BSI replacement only after confirmation.
Likely causes
- Worn or damaged transponder in key (most common)
- Weak/flat key battery preventing remote authentication
- Faulty antenna ring or wiring at ignition barrel
- Communication fault on CAN between BSI/immobiliser and engine ECU
- Software mismatch after module replacement or incomplete key programming
Fault status
Status
Immobiliser system fault or immobiliser active — engine start inhibited until key recognition/communication fault is resolved. Check key, antenna, immobiliser/BSI and related communications.
Repair difficulty: Medium
Diagnostic time: 0.5-3.0 hours
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