Code
B2693
Generic
B — Body
Immobilizer: Transponder Key ID Mismatch
AI status
Completed
Completed
100%
Causes
- Using an unprogrammed or wrong transponder key
- Corrupted or erased immobilizer key ID memory
- Damaged key transponder (internal coil or chip failure)
- Faulty or weak antenna/coil in the ignition cylinder or reader ring
- Poor electrical connection (power, ground) to the immobilizer module or antenna
- Faulty immobilizer control module or ECU logic
Symptoms
- Engine will not start or cranks but does not run
- Security/immobilizer warning lamp or message on dash
- Intermittent no-start condition with specific key
- Starts normally with known-good programmed key (if available)
- No crank in some systems if immobilizer disables starter
- Remote keyless functions may still work (depending on system)
What to check
- Verify vehicle owner has correct, programmed key(s); try known-good/spare key
- Check battery voltage (vehicle and key fob) to ensure adequate power
- Use an OEM-level scan tool to read immobilizer fault memory and list of stored key IDs
- Check for recent entries/events showing 'Key ID mismatch' or key learn events
- Inspect antenna/reader ring at ignition barrel for damage, corrosion, or loose connector
- Check connectors, power and ground at immobilizer module and antenna coil
Signal parameters
- Transponder key ID read by antenna vs. authorized key IDs stored in immobilizer
- RF/reader field presence and amplitude at the antenna
- Antenna coil resistance and continuity
- Immobilizer module supply voltage and ground voltage
- CAN/serial messages: immobilizer status, key ID, authorization result
- Key learn/erase event logs and timestamps
Diagnostic algorithm
- Confirm customer key usage and try all available keys to determine if problem is key-specific.
- Check vehicle battery voltage and key fob battery; low voltage can prevent reliable reads.
- Scan immobilizer and ECU for stored codes and stored key IDs; note mismatch events and timestamps.
- Use scan tool to request/compare the transponder ID read by the immobilizer with the list of authorized IDs.
- Visually inspect ignition reader/antenna for physical damage, corrosion, or loose connectors; measure antenna coil continuity/resistance.
- Verify power and ground at immobilizer module and antenna connector; repair poor connections as needed.
- Monitor communication bus (CAN/serial) between immobilizer and engine control module while attempting a start; check for message timeouts or errors.
- Attempt to start vehicle using a known-good, programmed key. If that key works, suspect key or key programming.
- If key is unreadable or unprogrammed, reprogram key using OEM key learning procedure (follow manufacturer security procedures).
- If reprogramming fails or authorized IDs are missing/corrupt, consider immobilizer module replacement or module reprogramming as per manufacturer instructions.
- Inspect for aftermarket devices (alarms/remote starters). Remove or disable them to verify they are not causing interference.
- After repairs, clear faults and repeat tests to confirm the system accepts the key and the vehicle starts reliably.
Likely causes
- Using an unprogrammed/spare key or wrong key
- Damaged or unreadable transponder in the key
- Faulty/damaged antenna or reader coil around ignition
- Poor connector or power/ground to the immobilizer module
Fault status
Status
Immobilizer — Transponder key ID mismatch: key not authorized by immobilizer/ECU.
Repair difficulty: Medium
Diagnostic time: 0.5 - 2.0 hours
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