Description And Operation: Notes
DESCRIPTION
The electric hydraulic power steering system is made up of the following components:
| 1. | Refer to ELECTRIC HYDRAULIC POWER STEERING (EHPS) PUMP . |
| 2. | Fluid Reservoir |
| 3. | Refer to BODY CONTROL MODULE (BCM) . |
| 4. | Steering Column |
| 5. | Refer to INSTRUMENT PANEL CLUSTER (IPC) . |
| 6. | Refer to STEERING COLUMN CONTROL MODULE (SCCM) . |
| 7. | Steering Wheel |
| 8. | Intermediate Shaft |
| 9. | Steering Gear |
| 10. | Steering Linkage |
| 11. | Fluid Lines |
| 12. | Steering Damper |
OPERATION
Multiple modules work together to improve vehicle steering assist at different rates at different speeds. At slow speeds, such as parking maneuvers, more assist is available and at high speeds less assist is available. The EHPS module uses the Controller Area Network-Chassis (CAN-C) and Controller Area Network-Interior High Speed (CAN-IHS) data bus for inputs and outputs of the information necessary for operation. The use of a scan tool is necessary for diagnostics. EHPS module faults are stored in a diagnostic program memory and are accessible with the scan tool. Faults remain in memory until cleared, or until after the vehicle is started approximately 50 times. Stored faults are not erased if the battery is disconnected.
The EHPS pump assembly contains a control module, brushless electric motor, and hydraulic pump integrated into a single unit. The EHPS pump draws power from the 12 volt electrical system and provides the necessary flow and pressure to the steering gear to provide normal power steering. The output flow of the EHPS pump is varied as a function of steering wheel rate and vehicle speed in order to provide the optimum flow of power steering fluid to the steering gear under all operating conditions. The EHPS pump will start to provide steering assist when the vehicle speed message showing greater than 5 km/h (3 mph) is received on CAN-C. If the vehicle speed message is missing at vehicle startup, the EHPS pump will not operate. If the vehicle speed message is lost during operation the EHPS pump 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 pump 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 pump will resume normal operation automatically once any missing message or out of range condition noted above is restored to normal.
The EHPS warning lamp is used to visually indicate the fault/fail status of the EHPS system. The EHPS system is capable of controlling hydraulic output flow as a calibrated function of Engine Stop Start (ESS) status.