This is done by removing the electric assist form the steering components and see if the noise disappears or changes. In this case, you'd separate the assist portion of the system from the actual mechanical components and see if the problem changes or goes away. If the problem is a mechanical one, the diagnostic process is very similar to that of a hydraulic system. They range from mildly annoying to downright scary so it's important to locate the cause of the problem quickly. Mechanical EPS problems show up as noises, vibration or other physical steering system faults. And it's relatively simple to figure out which of the three is causing the problem. Problems in the EPS system usually come down to one of three things: mechanical problems, electrical problems, or sneaky problems that fool you into thinking they're steering-related when they're actually caused by another system or component. But there are a few tips that really can help speed up the diagnostic process. One important thing to note: Because the motor isn't designed to handle extremely high power for extended periods of time (for example, turning from lock to lock repeatedly while the vehicle is stationary), the EPS system will protect itself by limiting the amount of current commanded to reduce system temperature - and unfortunately, limiting assist in the process.Īs always, a good scan tool, service information, TSBs and calibration updates all are important for successfully repairing the vehicle. The PSCM combines inputs such as steering shaft torque sensor, vehicle speed (via serial data), calculated system temperature, and steering tuning setting to determine the amount of assist required - for example, greater assist would be provided at slow-speed parking than during a high-speed lane change - and commands the correct amount of current (or assist) to the power steering motor. The steering motor itself is typically a DC, reversible motor that provides assist through a worm gear and reduction gear. One thing to be aware of is that the PSCM uses the Steering Wheel Position Sensor to "locate" the on-center position and will actually provide a small amount of electrical current to "return" to the center position (not beyond the center position though). The Signal 1 and Signal 2 voltages increase and decrease, staying within 2.5 to 2.8 volts of each other as the steering wheel is turned. The steering wheel position sensor is a five-volt, dual analog signal device, but this one operates between 0V to 5V. The PSCM interprets the change in signal voltages as "steering direction" and steering column shaft "applied torque." Simple, really. Turning to the left decreases Signal 1 Voltage and increases Signal 2 Voltage. Turning the steering wheel to the right increases Signal 1 Voltage and decreases Signal 2 Voltage. It sounds complicated, but it really isn't. This sensor is a five-volt, dual analog inverse signal device operating between 0.25V and 4.75V (as many five-volt reference sensors do – voltage outside of this range usually indicates a circuit problem and sets a DTC). Getting extremely technical, the torque signals are determined by the relative position between the upper and lower rotors of the sensor. The steering shaft torque sensor (located in a section of torsion bar in between the steering input and output shafts) is the Power Steering Control Module's (PSCM) main input for determining steering direction and the amount of assist needed. The EPS system is more efficient than hydraulic systems since it only needs to provide assist when the driver is actually steering (rather than robbing energy from the vehicle's engine to rotate the hydraulic pump constantly), and it keeps the environmentalists happy since there's no harmful fluid involved that needs to be flushed or drained. EPS simply uses an electric motor to provide the assist rather than use a hydraulic pressure system. The idea behind EPS is the same as the idea behind hydraulically assisted power steering systems: reducing the amount of effort needed to turn the steering wheel. And that means that you need to know how the system works, what goes wrong and how to fix it – quickly, safely and profitably. Because the system is such a fuel-saver and also lowers emissions, it's turned up on most of the vehicles on the road. Interestingly, it's not just expensive or luxury models that use EPS. GM vehicles have used electric power steering (EPS) systems for over a decade now, so odds are good you've already worked on a vehicle using the system. Editor's Note: This article has been updated from its original 2011 version.
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