Initial Inspection and Diagnostic Overview
Steering System
Special Tool(s)
Principles of Operation
Variable Assist Power Steering (VAPS)
Navigator vehicles include a VAPS system that 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 4-Wheel Air Suspension Module (4WAS) 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 according to a look-up table internal to the module. The module pulse-width modulates the VAPS actuator current to provide the desired amount of assistance. The amount of hydraulic steering assistance provided by the VAPS subsystem is proportional to the average control valve current.
The vehicle speed is provided to the air suspension module through a transmission mounted vehicle speed sensor (VSS).
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. Inspect Tires
^ Check the tire pressure. For additional information, refer to the Vehicle Certification (VC) label.
^ Verify that all tires are sized to specification.
^ Check the tires for damage or uneven wear.
3. Belt and Tensioner Check
^ Refer to diagnosis and testing of the accessory drive system.
4. Fluid Level Check
^ 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. 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.
External Leak Check-Typical Power Rack-and-Pinion Steering Gear
6. External Leak Check
^ 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 the steering wheel at stops. Check for leaks. Repair as necessary if leaks are observed.
7. Turning Effort Check
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 alter 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 = AL1, ECUS NO RESP/NOT EQUIP, refer to Module Communications Network.
^ NO RESP/NOT EQUIP for 4WAS module, refer to Module communication 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 4WAS module.
13. If the DTCs retrieved are related to the concern, go to Diagnostic Trouble Code (DTC) Index to continue diagnostics. Diagnostic Trouble Code Tests and Associated Procedures
14. If no DTCs related to the concern are retrieved, GO to Symptom Chart to continue diagnostics. Symptom Related Diagnostic Procedures
15. If the fault is not visually evident, determine the symptom and GO to Symptom Chart Symptom Related Diagnostic Procedures.