B2799

Engine Immobiliser System Malfunction

Car Fault Codes Lexus Body

Can you still drive? No, stop right away

Who can fix it? Needs a specialist or dealer

Typical repair time 30 minutes – 4 hours

Typical cost SAR 150 to 5,500

What it means

This is a code specific to Lexus (and the Toyota group); the same number may mean something different on other makes. It means the immobiliser could not complete its handshake with the engine computer, either because communication between them failed or because the ID codes do not match. The system therefore blocks starting or stops the engine after a moment to protect the car from theft.

Models covered: Lexus models with a transponder-key immobiliser.

Symptoms4

Engine will not start although the starter turns, or it dies after a few seconds.
Security indicator on the dash stays on or flashes unusually.
A key or system warning message on some models.
The check engine light may come on.

Possible causes6

Unregistered key or a transponder damaged by a drop or water.
Weak key fob battery on models with a smart key, affecting key recognition.
Interference from other keys or electronic devices nearby.
Wiring or connector fault between the immobiliser unit and the engine computer.
A used engine computer or immobiliser unit installed without re-registration.
Weak vehicle battery.

How to diagnose5

Try the second key; with a smart key, use the weak-key-battery starting method in the owner's manual.
Check the vehicle battery and its voltage while cranking.
Read immobiliser and engine computer codes with a Lexus-capable scan tool.
Inspect connectors and wiring between the system units.
Review any recent computer or key work that may have left the system unregistered.

How to fix5

Replace a weak key fob battery and use a working key.
Charge or replace the vehicle battery.
Repair faulty connectors or wiring.
Register keys or the engine computer at a dealer or qualified programmer.
Clear the codes and confirm starting with every registered key.

Repair cost

0–500

500–2,000

2,000–5,000

5,000+

In Saudi riyals; the highlighted part is the expected range for this fault.

A key or vehicle battery or a connector repair is at the low end; a new Lexus key with programming or computer registration needs dealer tools and can exceed the general price table.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions

I fitted a used engine computer to my Lexus and got B2799. Why?

The engine computer carries an ID tied to the original car's immobiliser. It must be registered to your car with the proper tool, or it will not allow the engine to run.

Is replacing the key battery enough?

Only if a weak battery was stopping the key from being recognized. If the problem remains with a new battery and with the other key, the cause is in the system or its registration.

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This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.

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