A vehicle guidance system comprises a hydraulic steering cylinder for controlling a steering angle of a steerable wheel of a vehicle. A hydraulic steering valve is adapted to control a flow of hydraulic fluid to the hydraulic steering cylinder. A stepper motor is adapted to move or modulate a shaft coupled to the hydraulic steering valve in accordance with a control signal or control data message from a vehicle guidance controller. A position encoder of the stepper motor can measure the movement of the shaft. A steering angle estimator can estimate the steering angle based on measurements of the position encoder. A location-determining receiver provides position data and heading data. A vehicle guidance controller provides the control signal or control data message based on the estimated steering angle, position data and heading data.