The B2799 DTC is a manufacturer-specific code on Toyota cars. When the code is triggered, it relates to the Key Transponder, the vehicle computer, and the Immobilizer system.
These electrical components are vital for the car’s ignition system. They also serve as a safety precaution installed by the manufacturer to reduce car theft.
In addition, there is constant communication between the transponder, the vehicle’s computer, and the immobilizer system whenever the key is placed in the ignition. The code will come up when there is a distortion in the communication of these components.
This article compiles a useful guide on the B2799 code in Toyota vehicles, its causes, symptoms, and how to fix the problem.
Here Is What the B2799 DTC Means on Your Toyota
The B2799 is a DTC code that stands for Engine Immobiliser System Malfunction. It is a manufacturer-specific code for Toyota and will come up when there is a communication problem between the Engine Control Unit (ECU), Immobilizer Control Module, and transponder key. The code will also come up when there is a disruption between one or more communication lines linking the ECU and the transponder key.
Not sure what a transponder key is? In that case, it is a device that uses a Radio Frequency Identification (RFID) chip to transmit low-level signals from your Toyota key and is part of the manufacturer’s anti-theft security.
The code comes up when the ECU cannot communicate properly with the transponder key. The transponder key works by sending coded data to the ECU.
A communication system is put in place between the ECU and the transponder to ensure that the code sent by the transponder key reaches the ECU. The key works with the ECU and Immobilizer Control Module (ICM). The ICM is the computer system that ensures that the transponder key sends the correct code.
When the key is placed in the ignition, the transponder sends a series of codes to a receiver located in the ECU. Then the code is verified, and the vehicle will start perfectly.
However, suppose the code does not match the preprogrammed code in the computer system. In that case, the immobilizer will disconnect or disable vital parts of the car responsible for ignition, like the fuel supply or ignition system.
If the computer disrupts communication between the ECU, transponder key, and ICM, then the engine will not start. The problem will also trigger the B2799 code.
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What Are Possible Causes of a B2799 Code on Toyota?
Many factors can cause the B2799 code to come up. Many of these factors are related to the transponder key, ECU, and ICM. Below are possible causes of the error code B2799.
Damaged or defective transponder key amplifier
One of the major causes of the B2799 code is a damaged transponder key. Once the transponder key amplifier is damaged, the code stored in the transponder is not sent to the receiver. When this happens, the system senses that a key is trying to start the vehicle but will not ignite the engine; it will also trigger the code.
Faulty Transponder Key Electronic Control Unit (ECU)
When the transponder key is inserted into the ignition, the ECU sends a signal to the key, and in turn, the key sends the programmed code. The code will come up when there is a communication problem between these.
Damaged wiring and /or connectors anywhere in the security/anti-theft system
The wiring harness plays a major role in carrying the required electrical current to the needed components, while other wiring plays a major role in aiding communication between these parts.
When the wiring is damaged, two things can happen. The first is that the ECU and ICM may not function because the electrical current wiring harness is damaged. Also, if the wiring around the area is damaged, there could be a disconnect between these components.
Low voltage due to weak battery
Another major problem that could affect the effective communication between the ECM, ICM, and the transponder key is a low voltage supply. The systems are electric components and make use of a specific voltage. When the voltage supplied goes below their specified voltage, the ECU and ICM will not function well, causing the code to be thrown.
Faulty immobilizer control module
The immobilizer Control Module disables the ignition system or fuel system when the code sent by the transponder does not match that in the system. The ICM communicates with the ECU to be able to achieve its functions. When there is a problem in the communication between the two computer systems, or the ICM is malfunctioning, the ECU will throw the B2799 trouble code.
Faulty ECM
The ECM plays a major role in the proper functioning of the transponder key. It receives the code sent by the key through a receiver. After receiving the code, it compares the code sent with the system’s program.
When the ECM malfunctions, it will not be able to properly verify the code sent by the key transponder. When this happens, that system will throw the code showing problems with the transponder key communication with the ECU.
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What Are the Possible Symptoms of a B2799 DTC?
When the B2799 comes up, it is accompanied by some symptoms. These symptoms make driving your vehicle difficult and, in most cases, impossible. When the code is thrown, you need to fix the problem immediately.
Engine cranks but no start
One major symptom of a B2799 code is that your vehicle will crank but not start. It could be due to a damaged communication system, the wiring connecting the PCM and the key transponder, a damaged transponder, or other important parts.
When this happens, the ECM and ICM must receive the codes to ignite the engine. The ICM then continues to disable the ignition system.
The engine keeps shutting off
When your engine keeps switching off when the B2799 code comes up, the ICM continues to disable the fuel injection system and other parts of the engine responsible for ignition and keeping the engine running. At this point, the problem could result from a faulty ICM or malfunction.
Also, a damaged ECM could cause the engine to switch off repeatedly if the ECM sends wrong signals to the ICM. There are also many other ways that the ECM could cause this problem, knowing that the ECM controls a larger part of the engine.
Error codes and warning lights
When a problem with the key transponder arises, it comes with related codes and warning lights. A major warning light that comes on is the amber key warning light. It signifies that there is a failed attempt to ignite the engine.
Engine light could also come up, especially when the problem is due to the ECM or ICM.
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What Should You Do If You Get This Code?
When you get the code, you need to make a proper diagnosis to find the cause of this code. As we know, several things can cause the code to get triggered.
The first parts of your vehicle that you should check when you get the code are the key transponder, ECM, and ICM. These components are often associated with a B2799 trouble code.
If the problem is unrelated to the above cause, you may have a wiring problem. The wires play a major role in every vehicle. The wiring harness in and out of the antitheft or security system carries electric power and relays information.
If the wire gets damaged, the needed components will not get the electric power and may also be unable to communicate between themselves.
Also, it would help if you got your key checked; a damaged transponder key will also get the code triggered because it will not be able to send the needed code to the ECM.
Once the various components have been checked and you can recognize where the fault is coming from, it will be easier to fix and get your vehicle going again.
How to Fix This Error Code?
There are various ways to fix the error code, but the best way is to solve the underlying cause of the code. As we know, some causes can throw the code, but once you recognize or diagnose the particular cause of your vehicle’s B2799 trouble code, you are a step closer to fixing the problem.
If the problem is due to a malfunction or faulty ECM or ICM, it could be due to a faulty wiring harness. Check the wiring harness, and if it is corrupted or broken, then you will have to get the harness replaced immediately.
After changing the wiring harness, and the error does not go away, you may have to replace the ECM. It might cost you a lot, but it is worth it as it will save you from a lot of trouble in the future.
Furthermore, you should properly check the key transponder to see if it is damaged. Once the transponder is damaged, you must get a new key. You can do this by visiting a certified Toyota repair shop.
You can make the repair much easier if you take your vehicle to a professional once you detect the code. Unfortunately, fixing this trouble code is not easy; some people might lack the skills and knowledge to make it a DIY task.
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Closing Thoughts
When the B2799 code comes up in your Toyota, fix it urgently, as it has serious implications for your car’s drivability. The code has some symptoms that make it difficult or impossible to drive the vehicle. Once you get the code, get a proper diagnosis or have your vehicle checked by a certified mechanic.
Mark is a senior editor for Mechanic Ask, creating tech-focused articles about diagnostics, tools, and new auto servicing methods. He attends industry shows to stay current. With a mechanical engineering degree, Mark is able to translate complex technical details into explanations understandable for shop owners and technicians. His articles help shops improve processes, reduce costs, and boost productivity.
