Theory Of Operation

The Electro-Hydraulic Power Steering (EHPS) Assembly contains a control module, brushless electric motor, and hydraulic pump integrated into a single unit. The EHPS Assembly draws power from the 12-Volt electrical system and provides the necessary flow and pressure to the steering gear to provide normal power steering independent of the gasoline engine. The EHPS Assembly requires communication over the CAN C bus to function properly. The output flow of the EHPS Assembly is varied as a function of Steering Wheel Rate (received from SAS Module) and Vehicle Speed (received from ABS Module) in order to provide the optimum flow of power steering fluid to the steering gear under all operating conditions. The pump will start to provide steering assist when a hybrid active (vehicle started) or a Vehicle speed message greater than 5 kph (3 mph) is received on CAN C. If both the Vehicle Speed and Hybrid Active messages are missing at vehicle startup, the EHPS Assembly will not operate. If the Vehicle Speed message is lost during operation the EHPS Module will use a default vehicle speed of 85 km/h (59 mph) to calculate desired flow and as a result, steering effort will no longer be speed sensitive. If the Steering Wheel Position message is lost the EHPS Module will use a default steering wheel rate of 230°/sec to calculate desired flow and as a result, steering effort may be higher on evasive steering maneuvers. The EHPS Assembly will resume normal operation automatically once any missing message or out of range condition noted above is restored to normal.