You might think that the fuel sender in the tank is directly connected to the gauge in the instrument cluster. On older vehicles, you would be right. But on late-model vehicles, you would be wrong the majority of the time.

On most newer vehicles, the fuel level sender is connected to a module that calculates the fuel level in the tank. Why?

Here are three reasons. First, the fuel level changes due to acceleration, braking and cornering. If a sender was directly connected to the gauge, it would be jumping all over the place. I could be a real distraction for the driver. So instead, the calculation is measured when the vehicle is at a steady-state, like at a stoplight or traveling at a constant speed.

Second, the fuel level is calculated for use in EVAP testing. Many evaporative emissions monitors that are non-continuous are performed when the tank is at a specific level that is not too full or not too low. This is why knowing the level of the fuel is critical.

Third, fuel tanks have changed. A saddle-style fuel tank is mounted under the rear seats on many vehicles with a rear driveshaft and differential. The tank is connected at the top, but there are two separate wells on either side of the driveshaft.Each well has a fuel pump and level sensor. One pump supplies fuel pressure to the engine. The other pump will transfer fuel as needed to the side of the tank.

With these tanks, fuel levels can be drastically different. So, the fuel level is calculated for the gauge.When replacing a fuel pump assembly with a sender, make sure the fuel level is accurate by using a scan tool. Also, use a high-quality fuel pump tested at the factory for accuracy.

This video is sponsored by Carter Fuel Systems.