2024 BMW M340i Fuel Temperature Sensor Replacement Cost

With the flexibility of computerized control systems for modern vehicles, manufacturers have nearly limitless control over engine operation and a more broad ability to tune the operation of the engine's accessory systems in order to maximize the fuel that is used during combustion. One way of maximizing the efficiency of the engine is to measure the amount of fuel used per combustion event, but taking it a step further requires that the temperature of the fuel is known. The fuel temperature sensor will read the temperature of the fuel going into the engine to determine exactly how much should be used. Let's look at how this is done.

To understand the purpose and function of the fuel temperature sensor, it is essential to understand the chemical properties of oxygen and fuel, as well as the laws of thermodynamics that play on all substances, including fuel and oxygen. Fuel and oxygen can only burn efficiently in exact amounts. This is known as the stoichiometric ratio, and it is basically a measurement of how much oxygen must be used to completely burn a given amount of fuel inside the engine. However, the amount of fuel and oxygen cannot be measured only by volume for high accuracy, but they must be measured by volume while accounting for heat expansion. Since the temperature of the fuel and air is known, the computer is not just calculating the air to fuel ratio based on volume, it can now calculate the air to fuel ratio on a molecular level, though this is would never be expressed. Plainly put: the fuel temperature sensor will allow the engine management computer to use precise and accurate measurements to ensure the most efficient burn of fuel possible.

Since the fuel temperature sensor is more of a component to maximize efficiency, the computer noticing the sensor is providing erroneous data can have one of two effects. First, the engine control module (ECM) will likely prevent the fuel temperature sensor from providing input, alert the driver with the check engine light, begin using more fuel to prevent a lean running condition, and the exhaust may smell strongly of gasoline while idling. If the fuel pressure sensor is reporting incorrect temperatures, but the temperature reported is within the specified range, the engine may begin to run rich or lean. In either case, the oxygen sensors will detect the rich or lean conditions, and the ECM will begin to run in a closed loop. This means that the fuel to air ratio will not be determined by the oxygen sensors, and this will certainly impact fuel economy and engine power. The check engine light will still illuminate as well.