What is OBD-II Code P23FB – Cylinder 10 Injector B Air-Fuel Ratio Imbalance

A Comprehensive Guide to OBD-II Code P23FB – Cylinder 10 Injector B Air-Fuel Ratio Imbalance

As a mechanic, I have come across several instances where a car’s engine light turns on, and the owner has no idea what it means. One such code is OBD-II Code P23FB – Cylinder 10 Injector B Air-Fuel Ratio Imbalance. In this article, we will explore what this code means, what could cause it, and how to repair the issue.

OBD-II Code P23FB – What is it?

OBD-II stands for On-Board Diagnostics, version 2. The OBD system is responsible for monitoring the car’s engine and detecting any malfunctions. When the OBD system detects a problem, it stores a diagnostic trouble code (DTC) in the car’s memory. This code helps mechanics identify the issue and fix it.

Code P23FB indicates that there is an imbalance in the air-fuel ratio of cylinder 10 injector B. The air-fuel ratio is the amount of air and fuel being mixed together in the car’s engine. If the ratio is too rich, there is too much fuel in the mixture, and if the ratio is too lean, there is too much air in the mixture. An imbalance in the air-fuel ratio can cause the engine to run less efficiently, lead to decreased gas mileage, and cause damage to the engine over time.

What Causes Code P23FB?

There are several potential causes of Code P23FB, including a problem with the fuel injectors, issues with the oxygen sensors, or issues with the engine’s coolant temperature sensor. Here are possible reasons:

Dirty Fuel Injectors: Fuel injectors can get clogged with dirt and debris over time, leading to a reduction in fuel flow and compromised air-fuel ratios.

Failed Oxygen Sensor: The oxygen sensor in the car’s exhaust system measures the amount of oxygen in the exhaust gas. If the oxygen sensor fails, it can cause inaccuracies in the air-fuel ratio that lead to engine problems.

Failure in the Engine’s Coolant Temperature Sensor: The coolant temperature sensor sends signals to the ECU to adjust the air-fuel ratio according to the engine’s temperature. A faulty sensor may produce wrong signals leading to imbalances in the air-fuel ratio.

Corroded Wiring: Corrosion on vital connectors and wiring could lead to weak signal transfer to the Fuel Injectors and Semsor, impairing their functionality.

How to Fix Code P23FB?

The course of action we take to rectify code P23FB is to execute a series of diagnostic tests to get to the root cause. Once the underlying factor is detected, the appropriate fixes can be initiated. Here are some of the corrective procedures we use to deal with this issue:

Cleaning the Fuel Injectors: We will use specialized cleaning agents to flush out any impurities and debris that might be clogging the fuel injectors. In addition, we assess the fuel pump, fuel filter, and fuel pressure regulators for routine diagnostics and end-to-end repair.

Replacing Failed Oxygen Sensor: If an oxygen sensor is faulty, we replace the component with a high-quality original equipment manufacturer (OEM) part for best results.

Replacing Faulty Engine’s Coolant Temperature Sensor: Upon verification, the faulty coolant temperature sensor is swapped out with a new one, and the component’s operation is evaluated.

Repairing Corroded Wiring: We inspect different connectors and wiring in the car’s system to locate any areas of corrosion or damage. We then replace the corroded or damaged components, ensuring full connectivity between the different components.

The Bottom Line

Code P23FB should not be taken lightly. Ignoring such codes can lead to engine damage and reduced gas mileage. Therefore, a professional mechanic should investigate the cause of the issue and repair it immediately to prevent further damage to the car. Additionally, it is advisable to conduct routine maintenance checks to prevent these issues from ever happening.


1. Can’t I just ignore Code P23FB, and the engine light will go off?
No, ignoring such codes can lead to serious engine damage and reduced gas mileage. Instead, take your car to a mechanic to repair the problem quickly.

2. What is the estimated cost of repairing Code P23FB?
The cost to repair P23FB varies depending on the underlying problem and the model of the car. For instance, replacing a faulty oxygen sensor would cost between $200 and $500. More complex repairs such as wiring damages can cost up to $1000.

3. Can I replace the car’s oxygen sensor myself?
Although it is possible to replace the failed oxygen sensor yourself, it is advisable to have a professional mechanic handle the task. Replacing the sensor involves intricate processes like sensor calibration, which requires special tools and machines that only professional auto mechanics possess.

4. How can I prevent code P23FB from recurring?
Routine maintenance, such as changing the oil and oil filter, can help prevent code P23FB from recurring. Avoid driving a car with low fuel levels and ensure you’re using high-quality fuel and proper fuel additives, as low-quality fuel can clog injectors over time.

5. What is the life expectancy of an oxygen sensor?
Oxygen sensors generally last between 80,000 and 100,000 miles. However, different factors, such as vehicle make and model and driving habits, might influence how long your oxygen sensor lasts.


1. Linke-Klein, H., Hahmann, K.G. & Petersen, H.B. Influence of air-fuel ratio on engine performance and exhaust emissions of lean-burn engine operating on biogas and gasoline. J Therm Anal Calorim 136, 607–614 (2019). https://doi.org/10.1007/s10973-018-7738-4

2. Diagnosing and maintaining your car support- OBD-II code P23FB. Valvoline Instant Oil. https://www.vioc.com/car-synthetic-oil-change-service-support/obd-ii-code-p23fb/

3. Hunter J., Auto Diagnosis and Repair: Understanding OBD-II Engine Codes. Delmar Cengage Learning, Albany, NY, 2001.

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