Circuit/System Description
The electronic brake control module (EBCM) controls the variable effort steering (VES) actuator on the steering gear. As speed increases the EBCM commands the amperage to the actuator to a max of 1A, this closes the orifice and restricts fluid flow for a firm steering effort. At low speeds and parking lot maneuvers the orifice is normally open allowing maximum fluid flow for an easy steering effort.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
- 5: This step tests the system for restrictions.
- 7: This step tests the following components for the following conditions: The pump for internal leaks The power steering pipes for kinks
- 8: This step tests the ability of the pump to regulate flow at maximum pressure.
- 10: This step tests the ability of the pump to regulate flow under normal operating conditions.
- 12: This step tests the internal components of the pump and the gear.
| Step | Action | Value(s) | Yes | No |
|---|
| DEFINITION: The Power Steering System Test Procedure will perform the following functions: Test the operation of the hydraulic power steering system. Test the operation of the power steering pump and power steering gear. Identify restrictions in the system. |
| 1 | Inspect the power steering fluid for the following indications of contamination: Milky fluid - water Brown fluid - burnt Debris in fluid - plastic or dirt Is the fluid free of contamination? | | Go to Step 3 | Go to Step 2 |
| 2 | Flush the power steering system. Refer to Power Steering System Flushing . Did you complete the procedure? | | Go to Step 3 | |
| 3 | NOTE: In order to accurately diagnose the system, the malfunction must be present during the test procedure. Attempt to duplicate the condition.Is the condition present? | | Go to Step 4 | System OK |
| 4 | Turn the ignition switch to the OFF position. Place a drain pan under the vehicle in order to catch any power steering fluid. Disconnect the power steering pressure pipe/hose from the power steering pump or the power steering gear as necessary. Install the J 44721 Power Steering System Analyzer (for Buick, GMC) or the SA9134C Power Steering System Analyzer (for Saturn) and the CH 48600 Power Steering Analyzer Adapters. See Special Tools . Fill the power steering system. Refer to Checking and Adding Power Steering Fluid . Did you complete the installation? | | Go to Step 5 | |
| 5 | Fully open the J 44721 or SA9134C valve. See Special Tools . Start the engine. CAUTION: Do not hold the steering wheel in the full turn position longer than 5 seconds, as damage to the steering pump may result. Turn the steering wheel and BRIEFLY hold the steering wheel against the steering stop in order to release any trapped air from the system. Inspect and ensure that all of the power steering pipe/hose connections are not leaking. Observe the pressure reading. Is the pressure reading greater than the specified value? | 1379 kPa (200 psi) | Go to Step 6 | Go to Step 7 |
| 6 | NOTE: A restriction may be present in the power steering system. Turn off the engine IMMEDIATELY. Locate and repair the restriction.Did you complete the repair? | | Go to Step 15 | |
| 7 | Allow the engine to run until the engine reaches full operating temperature. Record the pressure reading and flow reading. Partially close the J 44721 or SA9134C valve until the system pressure reaches the specified value, then record the FLOW reading. See Special Tools . Subtract second flow reading from the first flow reading. Is the flow DECREASE greater than 3.8L (1 gal) per minute? | 4827 kPa (700 psi) | Go to Step 11 | Go to Step 8 |
| 8 | CAUTION: Do not leave the valve fully closed for more than 5 seconds, or the pump could be damaged internally. Fully close then open the J 44721 or SA9134C valve 3 times. See Special Tools . Record all of the high pressure readings. Refer to Power Steering Pump Specifications for power steering system pressure relief specifications.Are the three high pressure readings within specifications? | | Go to Step 9 | Go to Step 13 |
| 9 | Are the three high pressure readings within 245 kPa (50 psi) of each other? | | Go to Step 10 | Go to Step 13 |
| 10 | Increase the engine speed to approximately 1600 RPM. Record the flow reading. Refer to Power Steering Pump Specifications for power steering system pressure specifications. Is the actual flow reading within specifications? | | Go to Step 11 | Go to Step 13 |
| 11 | Is the difference between the actual flow reading and the maximum flow specification more than 3.8L (1 gal) per minute? | | Go to Step 13 | Go to Step 12 |
| 12 | CAUTION: Do not hold the steering wheel in the full turn position longer than 5 seconds, as damage to the steering pump may result. Turn the steering wheel from steering stop to steering stop and record the FLOW readings at each stop.Is the flow LOWER than 3.8L (1 gal) per minute? | | Go to Step 15 | Go to Step 14 |
| 13 | Replace the power steering pump. Refer to Power Steering Pump Replacement . Did you complete the replacement? | | Go to Step 15 | |
| 14 | The power steering gear is leaking across the piston or bypassing the valve circuit. Replace the power steering gear. Refer to Steering Gear Replacement . Did you complete the replacement? | | Go to Step 15 | |
| 15 | Test the power steering system for the original condition. Does the original condition still exist? | | Go to Step 5 | Go to Step 16 |
| 16 | Disconnect and remove the J 44721 Power Steering Analyzer or SA9134C Power Steering Analyzer and the CH 48600 Power Steering Analyzer Adapters from the vehicle. See Special Tools . Connect the vehicle power steering pipes/hoses. Fill the power steering system. Refer to Checking and Adding Power Steering Fluid . Did you complete the procedure? | | System OK | |
| NOTE |
|---|
| In order to accurately diagnose the system, the malfunction must be present during the test procedure. |
| CAUTION |
|---|
| Do not hold the steering wheel in the full turn position longer than 5 seconds, as damage to the steering pump may result. |
| NOTE |
|---|
| A restriction may be present in the power steering system. Turn off the engine IMMEDIATELY. |
| CAUTION |
|---|
| Do not leave the valve fully closed for more than 5 seconds, or the pump could be damaged internally. |
| CAUTION |
|---|
| Do not hold the steering wheel in the full turn position longer than 5 seconds, as damage to the steering pump may result. |
Variable Effort Steering System Description and Operation
The Variable Effort Steering (VES) System varies the amount of effort to steer the vehicle as wheel speed changes or lateral acceleration occurs. The electronic brake control module (EBCM) controls an actuator located in the steering rack and pinion. The actuator consists of an electromagnetic coil and a normally open pintle valve. The valve regulates an orifice that bleeds inlet pressure through a return passage to regulate the amount of pressure available for steering assist. The EBCM commands current from 0-1 amp to the VES actuator which varies the amount of effort required to steer the vehicle. At high speeds, 1 amp of current is commanded to the VES actuator and the pintle valve is fully closed which provides minimum pressure for a firm steering feel and directional stability. The VES system uses the steering wheel position sensor input to calculate lateral acceleration during abrupt driving maneuvers. The system also uses the antilock brake system (ABS) wheel speed sensor inputs to determine vehicle speed. The EBCM is constantly monitoring these inputs to achieve the desired current to the VES actuator. The EBCM has the ability to detect malfunctions in the VES actuator or the circuits to the actuator. Any malfunctions detected will cause the VES outputs to be disabled, and the actuator will return to an open state. The EBCM will command the driver information center (DIC) to display the SERVICE STEERING SYSTEM warning message via a serial data circuit.
