Principles of Operation
Power Steering - The power steering system uses a vane-type pump to move the fluid from the reservoir to the rack-and-pinion steering gear and through the rest of the steering hydraulic system. The power steering pump is mounted to the engine and driven by the engine accessory drive belt. Power steering fluid is pulled into the pump from the reservoir. The power steering fluid is trapped between the pump vanes and moved to the high-pressure side of the pump creating a flow of fluid. The restriction of this flow by the steering gear creates the pressure that provides the steering assist. A combined pressure relief/flow valve is built into the pump to control the maximum pressure and flow provided to the steering system. This action prevents damage to the system and provides the correct level of assist during all engine speeds. While under pressure, the power steering fluid flows through the high-pressure power steering line to the steering gear. The fluid exits the gear and flows through the return line, cooler and finally to the reservoir. The reservoir slows the fluid, allows air to escape and filters the fluid before returning it to the pump.
Fuel Efficient Power Steering (FEPS) - The fuel efficient power steering (FEPS) system reduces vehicle fuel consumption by reducing the amount of power steering assist provided at higher engine speeds, when less assist is needed. The FEPS system is controlled by the steering effort control module (SECM), FEPS solenoid/actuator and the steering wheel rotation sensor. The steering wheel rotation sensor is mounted to the steering column. As the steering wheel is turned, the sensor generates a turning rate signal. On vehicles equipped with interactive vehicle dynamics (IVD) the rotation sensor is hard-wired to the ABS module. The ABS module sends the turning rate signal to the SECM over the high-speed controller area network (HS-CAN) bus. On vehicles not equipped with IVD, the rotation sensor is hard-wired to the SECM so the module receives the turning rate signal directly from the sensor. The SECM also receives vehicle speed information from the PCM over the HS-CAN bus. The SECM uses both of these signals to determine how much assist is needed. At slower speeds, full power steering assist is provided. As vehicle speed increases, the SECM sends a signal to the FEPS solenoid/actuator, which is mounted to the power steering pump. The FEPS solenoid/actuator is then activated to reduce the flow of power steering fluid through the power steering system. Power steering pump effort is reduced, which, in turn, reduces the pumps demands on the engine. With less load on the engine, the vehicle has greater fuel efficiency.
Steering Effort Control Module (SECM) - The SECM monitors vehicle speed and steering wheel rate to determine the correct amount of fluid flow provided to the system. When the driver is turning the steering wheel slowly, the module sends current to the solenoid/actuator on the power steering pump to reduce fluid flow from the pump. This reduced fluid flow decreases the back pressure in the power steering system, which reduces the power needed to drive the pump. When the driver turns the steering wheel quickly, the module reduces the current to the solenoid/actuator, which increases the pump flow to provide acceptable steering efforts. If the SECM detects a problem, the default mode is full flow (0 current).
The vehicle speed is provided to the SECM by the ABS module over the HS-CAN bus.
Steering Wheel Rotation Sensor - The steering wheel rotation sensor measures the rate of rotation of the steering wheel by monitoring the steering wheel rotation ring as it passes through the sensor gap. On vehicles not equipped with interactive vehicle dynamics (IVD), the steering wheel rotation sensor is wired directly to the SECM and sends the information about how far the steering wheel is being turned directly to the module. On vehicles equipped with IVD, the steering wheel rotation sensor is hard wired to the ABS module instead of the SECM and the ABS module sends the information to the SECM over the HS-CAN bus. For information on ABS and IVD, refer to VEHICLE DYNAMIC SYSTEMS article.
The rotation sensor receives power from the battery junction box (BJB) and is grounded through the SECM (on vehicles without IVD) or through the ABS module (on vehicles with IVD).
Normal Operation
Fused battery voltage is provided to the steering effort control module (SECM) from smart junction box (SJB) fuse 13 (7.5A) along circuit SBP13 (GY/RD). Fused ignition switch voltage is provided to the SECM from SJB fuse 35 (10A) along circuit CBP35 (YE/GY). Ground for the module is provided along circuit GD148 (BK/YE) and the module communicates with the other modules on the high-speed controller area network (HS-CAN) bus along circuits VBR04 (WH/BU) and VBR05 (WH).
- DTC B1317 Battery Voltage High - With the ignition key in the RUN position, if battery voltage exceeds 16.5 volts for more than 1,000 ms, DTC B1317 will be set.
- DTC B1318 Battery Volage Low - With the ignition key in the RUN position, if battery voltage falls below 8.5 volts for more than 1,000 ms, DTC B1318 will be set.
This pinpoint test is intended to diagnose the following
- Fuse(s)
- Wiring, terminals or connectors
- SECM
The steering effort control module (SECM) sends voltage to the power steering valve solenoid along circuit CCS11 (GN/WH), the voltage passes through the solenoid and returns to the SECM along circuit CCS12 (VT/GN). The power steering valve solenoid then controls power steering assist by regulating the flow of power steering fluid in the power steering pump. Depending on the returning current, the SECM will be able to detect if the solenoid is functioning correctly.
| DTC Description | Fault Trigger Conditions |
|---|---|
| DTC C192A Solenoid Actuator Circuit Failure DTC C192B Solenoid Actuator Circuit Open DTC C192C Solenoid Actuator Circuit Short to Battery DTC C192D Solenoid Actuator Circuit Short to Ground DTC C1933 Solenoid Current Out of Range | If the SECM detects an open, short to battery voltage or short to ground in the solenoid actuator or the actuator circuits during normal operation or during an on-demand self test, DTCs C192B, C192C, C192D or C1933 will set. If the SECM does not detect the desired current returning from the solenoid actuator during normal operation, DTC C192A or C1933 will be set. |
This pinpoint test is intended to diagnose the following
- Wiring, terminals or connectors
- Power steering valve solenoid
- SECM
On vehicles not equipped with interactive vehicle dynamics (IVD), the steering wheel rotation sensor is hard-wired to the steering effort control module (SECM) and sends the steering wheel position information to the SECM along circuits VCS06 (GY/BU) and VCS07 (VT/OG). On vehicles equipped with IVD, the rotation sensor is hard-wired to the ABS module. For IVD equipped vehicles, refer to VEHICLE DYNAMIC SYSTEMS article.
| DTC Description | Fault Trigger Conditions |
|---|---|
| DTC C195A Steering Angle Sensor Circuit Short to Battery DTC C195B Steering Angle Sensor Circuit Short to Ground DTC C1955 Steering Angle Sensor Circuit Open DTC C1956 Steering Angle Sensor Circuit Failure | If the SECM detects an open, short to battery voltage or short to ground in the steering wheel rotation sensor circuits during normal operation or during an on-demand self test, DTCs C195A, C195B or C1955 will set. If the SECM does not detect any current returning from the steering wheel rotation sensor during normal operation, DTC C1956 will be set. |
This pinpoint test is intended to diagnose the following
- Wiring, terminals or connectors
- Steering wheel rotation sensor
- SECM