The electric power steering (EPS) system reduces the amount of effort needed to steer the vehicle. The steering column is integrated with an assist mechanism which contains a hub gear fitted onto the lower steering shaft. The hub gear mates with a worm gear that is driven by the EPS motor, which is serviced separately from the steering column. The steering column is serviced as a complete assembly only. Disassembly of the column beyond the procedures included may lead to malfunction of the steering system.

Assist Mechanism

The assist mechanism is located at the bottom of the steering column. It contains the assist mechanism input shaft (driven by the EPS motor), the lower steering shaft, the hub gear and both the torque sensor and the steering position sensor. These sensors provide information to the power steering control module (PSCM), which is serviced as a unit with the EPS motor.

Steering Shaft Torque Sensor

The PSCM uses the steering shaft torque sensor as its main input for determining steering direction and the amount of assist needed. The steering column has an input shaft, from the steering wheel to the torque sensor, and an output shaft, from the torque sensor to the steering shaft coupler. The input and output shafts are separated by a section of torsion bar, where the torque sensor is located. The sensor is a 5-volt dual analog inverse signal device with a valid signal voltage range of 0.25-4.75 volts. When applying torque to the steering column shaft during a right turn, the sensor signal 1 voltage increases, while the signal 2 voltage decreases within the valid signal voltage range. When applying torque to the steering column shaft during a left turn, the signal 1 voltage decreases, wile the signal 2 voltage increases within the valid signal voltage range. The PSCM recognizes this change in signal voltage as steering direction and steering column shaft torque.

Steering Wheel Position Sensor

The PSCM uses the steering position sensor to determine the steering system on center position. Since the motor/module provides a slight amount of return to center assist, the PSCM will command the motor/module to the steering system center position and not beyond. The sensor is a 5-volt dual analog triangle signal device with a valid signal voltage range of 0-5 volts. The sensors signal 1 and signal 2 voltage values will increase and decrease within the valid voltage range, and stay within 2.5-2.8 volts of each other as the steering wheel is turned.