Initial Inspection and Diagnostic Overview
Steering System
Special Tool(s)
Principles of Operation
Variable Assist Power Steering (YAPS)
The Variable Assist Power Steering (YAPS) system controls the level of power assistance available to the driver based on vehicle speed. Below 3.2 km/h (2 mph), full power steering assist is provided to lessen steering efforts and increase maneuverability. Between 3.2 km/h (2 mph) and 191 km/h (119 mph), steering assist will decrease gradually at a calibrated rate to raise steering efforts for increased directional stability and greater road feel. Above 191 km/h (119 mph), steering assist is constant.
The VAPS module outputs a Pulse-Width-Modulated (PWM) current to the control valve actuator. The control valve actuator controls the hydraulic valve that determines the amount of hydraulic assist provided to the steering gear. The amount of assistance provided varies with the control valve actuator current, which is based on vehicle speed.
The vehicle speed is provided to the VAPS module by the Powertrain Control Module (PCM).
Inspection and Verification
CAUTION: Do not hold the steering wheel at the stops for an extended amount of time. Damage to the power steering pump can result.
NOTE: Make the following preliminary checks before repairing the steering system:
1. Verify the customer concern by operating the steering system.
2. Check the tires.
^ Check the tire pressure.
^ Verify that all tires are sized to specification.
^ Check the tires for damage or uneven wear.
3. Check the belt and tensioner.
^ Refer to diagnosis and testing of the accessory drive system.
4. Check the fluid level.
^ Verify that the power steering fluid level is within the appropriate hot or cold range on the dipstick. Add MERCON Multipurpose (ATF) Transmission Fluid XT-02-QDX or MERCON equivalent.
5. Check for air bleeding.
^ Verify that there is no air in the power steering system. Run the engine until it reaches normal operating temperature. Turn the steering wheel to the left and right several times without hitting the stops. If any air bubbles are present, refer to Power Steering System Purging.
6. Check for external leaks.
^ With the ignition switch at OFF, wipe off the power steering pump, power steering pressure hose, power steering return hose, power steering fluid cooler and hose assembly and steering gear.
^ With the engine running, turn the steering wheel from stop-to-stop several times. Do not hold steering wheel at stops. Check for leaks. Repair as necessary if leaks are observed.
7. Check turning effort.
^ Refer to Turning Effort Test under Component Tests. Component Tests and General Diagnostics
8. Visually inspect for obvious signs of mechanical damage.
9. If an obvious cause for an observed or reported malfunction is found, correct the cause (if possible) before proceeding to the next step.
10. If the concern remains after the inspection, connect the Scan Tool to the Data Link Connector (DLC) located beneath the instrument panel, and select the vehicle to be tested from the Scan Tool menu. If the Scan Tool does not communicate with the vehicle:
^ Check that the program card is correctly installed.
^ Check the connections to the vehicle.
^ Check the ignition switch position.
11. If the Scan Tool still does not communicate with the vehicle, refer to the tester manual.
12. Carry out the DATA LINK DIAGNOSTIC TEST. If the Scan Tool responds with:
^ CKT914, CKT915 or CKT70 = ALL ECUS NO RESP/NOT EQUIP, refer to Module Communications Network.
^ NO RESP/NOT EQUIP for FEM, refer to Module Communications Network.
^ SYSTEM PASSED, retrieve and record the continuous Diagnostic Trouble Codes (DTCs), erase the continuous DTCs and carry out the self-test diagnostics for the FEM.
13. If the DTCs retrieved are related to the concern, go to Diagnostic Trouble Code (DTC) Index to continue diagnostics.
14. If no DTCs related to the convent are retrieved, proceed to Symptom Chart to continue diagnostics. Symptom Related Diagnostic Procedures
15. If the fault is not visually evident, determine the symptom and proceed to the symptom chart.