Description And Operation: Steering: Notes
DESCRIPTION
The Electric Power Steering (EPS) system consists of the following:
| 1. | Refer to STEERING WHEEL . |
| 2. | Refer to STEERING COLUMN CONTROL MODULE (SCCM) . |
| 3. | Refer to STEERING COLUMN . |
| 4. | Refer to INTERMEDIATE SHAFT . |
| 5. | Refer to COUPLING . |
| 6. | Refer to EPS RACK AND PINION STEERING GEAR . |
| 7. | Refer to TIE ROD - Inner. |
| 8. | Refer to TIE ROD - Outer. |
| 9. | Refer to BODY CONTROL MODULE (BCM) . |
| 10. | Refer to INSTRUMENT PANEL CLUSTER (IPC) . |
OPERATION
The standard equipment EPS system provides variable assist to the driver according to driver inputs and the vehicle speed while performing system diagnostic tests and providing this information to the vehicle electrical system. The steering gear includes a Steering Angle Sensor (SAS) which transmits the direction and the angle information on the Controller Area Network - Flex Data (CAN-FD) bus. The EPS module has primary and backup microprocessors with different software algorithms that provide Cyclical Redundancy Checks (CRC) to confirm the SAS position. The EPS warning lamp is used to visually indicate a fault status of the EPS system to the IPC.
The EPS system is a dry gear system, therefore EPS system does not contain any hydraulic components and as a result, the EPS system will not experience a hydraulic leak. If fluid is detected at the front of the vehicle, on or near the steering gear, investigate other systems.
Turning of the steering wheel is converted into linear (side-to-side) travel via the intermediate shaft and coupling at the steering gear, through the meshing of the helical pinion teeth with the rack teeth within the steering gear. The lateral travel pushes and pulls the tie rods to change the direction of the vehicle front wheels.
Power assist steering is provided by an electric motor and module connected to the steering gear. The EPS system provides variable assist for steering maneuvers based on several inputs:
- Steering wheel position and rate of movement from the SAS in the steering gear - counterclockwise is positive readings and clockwise is negative readings
- Steering wheel torque from the torque sensor in the steering gear
- Vehicle speed received from the Brake System Control Module (BSCM)
The EPS module monitors the EPS temperature and has the capability of requesting the engine cooling fan be turned on when the EPS temperature reaches the activation temperature of 125°C (257°F) to prevent an EPS module over-temperature condition from becoming active. When the EPS temperature goes below the activation temperature, the EPS will stop requesting the engine fan activation. During an over-temperature event, steering assist will be reduced until the EPS temperature is back within the expected operating range.
The steering gear is not serviceable and is replaced as a complete assembly. The inner and outer tie rods and the tie rod bellows are serviced separately from the steering gear.
Manual steering control of the vehicle can be maintained if power steering assist is lost, however, under this condition, steering effort is significantly increased.