Summary
B2799 is a Toyota/Lexus code indicating the engine immobilizer system cannot identify the key's transponder chip. The immobilizer ECU reads the key transponder during starting — if it doesn't recognize the code, it prevents the fuel injection system from operating. The most common cause is a faulty key transponder (30%), followed by an immobilizer amplifier (antenna coil) failure (25%) and a key registration issue (20%). The engine will crank normally but will not fire. The security/immobilizer indicator light on the dashboard will typically flash rapidly.
Severity: High — engine will not start
Safe to drive: Yes, if the engine is running — but the vehicle will likely not restart once turned off
Repair cost: $50–$400 depending on cause
DIY difficulty: Moderate
What does B2799 mean?
Toyota and Lexus vehicles use an engine immobilizer system to prevent theft. Each key contains a small transponder chip that communicates with an amplifier (antenna coil) mounted around the ignition lock cylinder. When the key is inserted and turned, the amplifier energizes the transponder, which responds with its unique encrypted code. The immobilizer ECU (or the ECM on some models) verifies this code against its stored list of registered keys.
B2799 is set when the immobilizer system fails to identify a valid transponder code. This can mean the transponder isn't responding, is responding with an incorrect code, or the communication between the amplifier and the immobilizer ECU has failed. Unlike a no-crank condition (which would indicate a starter or battery problem), the engine cranks freely but will not start because the ECM is withholding fuel injector operation per the immobilizer's instructions.
On Toyota/Lexus vehicles with push-button start, the system uses a key fob with a built-in transponder that communicates wirelessly with the smart key ECU. The same B2799 code can appear if the smart key system cannot verify the fob's identity — in this case, holding the fob against the start button (where a backup coil is located) may allow starting.