What does the presence of carbon monoxide in exhaust indicate?

The presence of carbon monoxide in exhaust is a strong indication of incomplete combustion occurring within the engine. This happens when there is not enough oxygen available to fully convert the fuel into carbon dioxide and water, resulting in the formation of carbon monoxide, which is a toxic gas. Efficient combustion ideally requires the right balance of fuel and oxygen; when this balance is disrupted, it leads to the production of carbon monoxide.

In a functioning combustion process, fuel should combust cleanly, producing mainly carbon dioxide and water vapor. Therefore, high levels of carbon monoxide in exhaust mean that the combustion process is not performing optimally, suggesting issues such as a malfunctioning air-fuel mixture, faulty injectors, or problems with the ignition system. This can have significant implications for vehicle performance, emissions compliance, and even driver safety due to the poisonous nature of carbon monoxide.