Methods for operating a control system of a vehicle and vehicle systems are provided. A method includes receiving a first output signal from a longitudinal accelerometer during a first travel condition of the vehicle including a first vehicle speed of the vehicle and a first road grade substantially equal to zero, wherein the first vehicle speed is a constant speed and the first output signal represents a first measurement including a first vehicle acceleration component and a bias offset component, receiving a second output signal during a second travel condition of the vehicle including a second vehicle speed of the vehicle and a second road grade, wherein the second output signal represents a second measurement including a second vehicle acceleration component and the bias offset component, and determining the bias offset component and gravity component to obtain an estimated road grade factor.