GM Service Manual Online
For 1990-2009 cars only

The Variable Effort Steering (VES) System or MAGNASTEER - (MAG-e)® varies the amount of effort needed to steer the vehicle as wheel speed changes. At low speeds, the steering is assisted by hydraulics only, which provides maximum steering assist for easy turning and parking maneuvers. At high speeds, steering effort is increased to provide firmer steering (road feel) and directional stability. The Electronic Brake Control Module (EBCM) controls an electromagnetic rotary actuator located in the steering rack and pinion. The EBCM varies the steering assist by adjusting the current flow through the actuator. The actuator adjusts the amount of steering assist to achieve a given level of effort to steer the vehicle. The VES system accomplishes this by subtracting torque on the input shaft to the rack and pinion. The main component of the system is an electromagnetic actuator, which consists of a pole piece, and an electromagnetic coil assembly. The VES system uses the antilock brake (ABS) wheel speed sensor inputs to the EBCM to determine the desired amount of steering assist. When the EBCM senses wheel speed, it commands a current that is most appropriate for each speed. This current then energizes the actuator. The EBCM commands current from zero amps to positive three amps. At low speeds, no current is commanded, and steering is assisted by hydraulics only. At high speeds, a positive current is commanded which creates steering resistance. Ignition voltage and ground are provided through the EBCM. The EBCM has the ability to detect malfunctions in the actuator or the circuitry to the actuator. Any malfunctions detected will cause the system to ramp to zero amps and steering will be assisted by hydraulics only.