Symptom Related Diagnostic Procedures
57.00 Power Steering - Fault diagnosisPreliminary checks
1. Prior to carrying out fault diagnosis of the steering system, the following checks must be carried out and remedial action undertaken as necessary:
^ Check that tires fitted are correct to specification.
^ Check/adjust tire pressures.
^ Check that wheel nuts are tightened to the correct torque.
^ Check/adjust front and rear wheel alignment.
^ Check all steering components for signs of impact damage; ensure that wheel arches are clear of mud and debris.
^ Check all steering ball joints, gaiters, dampers, springs, steering universal joints and steering box fixings for damage, wear and security; rectify as necessary.
^ Check/top-up PAS fluid level in reservoir, check fluid for contamination - fluid should be reddish/brown in color. If discoloration is evident, suspect faulty steering box seals or hoses.
^ Check reservoir filler cap for damage.
^ Check PAS pump drive belt for wear and that it is tensioned correctly.
^ Check brake pads for oil contamination/uneven wear, brake discs for condition and brake calipers for correct operation, sticking piston(s) etc.
^ Check all fluid pipes and hoses for chafing, leaks, corrosion and that they are routed correctly.
^ Check that carpets and wiring harnesses are not fouling steering column.
^ Carry out a short road test, during test, operate steering on full left and right hand lock. Check steering for unusual noises and vibration.
Fault diagnosis
1. Steering wheel misaligned when road wheels are in the straight ahead position:
^ Check/adjust front wheel alignment.
2. Free play at the steering wheel or the vehicle wanders from side to side on the road when the vehicle is steered straight ahead:
^ Check/tighten the steering wheel nut.
^ Check steering linkage for excessive play.
^ Check steering column universal joint(s) for wear and pinch bolts for correct torque.
^ Check steering box fixings for correct torque.
3. Vehicle veers to one side when driven on a level surface:
^ Check tires for uneven wear.
^ Check that the vehicle is not unevenly loaded or overloaded.
^ Check/adjust front wheel alignment.
^ Check for damaged or worn front suspension components.
^ Steering rack leaking internally - Carry out power steering pressure test.
^ Check alignment of front and rear sub-frames.
4. Poor self-centering:
^ Check steering column universal joint(s) for corrosion and wear.
^ Check that steering column nacelle is not rubbing on the steering wheel - Reposition nacelle.
^ Check that pinion dust seal is not fouling floor aperture/steering column and that seal is in good condition.
^ Check/adjust front wheel alignment.
5. Excessive steering effort required during low speed maneuvering/parking:
^ Engine idle speed too low - Adjust idle speed using T4.
^ PAS or fluid cooler hose(s) or pipe(s) restricted by debris - Replace hose(s) or pipe(s) as necessary.
^ Steering transducer is not closed - No feed voltage - Refer to the Circuit Diagrams.
^ Steering transducer is not closed - Cable fault -Refer to the Circuit Diagrams.
^ SCM (Steering control module) faulty Refer to the Circuit Diagrams.
^ PAS fluid delivery pressure/flow too low - Carry out power steering pressure test.
^ Internal fluid leakage - Carry out power steering pressure test.
6. Steering is heavy to turn when driving but is normal when vehicle is stationary:
^ Steering transducer opens too soon - Refer to the Circuit Diagrams.
^ Steering transducer opens too soon - Possible SCM (Steering Control Module) fault - Refer to the Circuit Diagrams.
^ Steering transducer opens too soon - Possible speedometer signal error - Check the speedometer circuit Refer to the Circuit Diagrams.
7. Steering is very light when driving but is normal when stationary maneuvering:
^ Steering transducer is not open - No PAS fluid flow - Check PAS fluid condition - possible contamination.
^ Steering transducer is not open - Possible SCM (Steering Control Module) fault - Refer to the Circuit Diagrams.
^ Steering transducer is not open - Possible speedometer signal error - Check the speedometer circuit Refer to the Circuit Diagrams.
^ PAS fluid reservoir filter blocked - Replace PAS reservoir.
8. Steering is heavy during rapid movement of the steering wheel:
^ Air entering from the feed side of the PAS system and becoming entrained in the PAS fluid.
^ Engine idle speed too low - Adjust idle speed using T4.
^ PAS fluid delivery pressure or flow too low - Carry out power steering pressure test.
9. Steering is heavy in either direction:
^ Lower steering column fouled by carpet or wiring harness.
^ Check/adjust front wheel alignment.
^ Faulty rotary valve/seal - Carry out power steering pressure test.
^ Tire(s) fouling wheel arch liner/suspension components.
10. Steering is heavy in both directions:
^ Air in PAS system - Bleed PAS system.
^ Engine idle speed too low - Adjust idle speed using T4.
^ Faulty rotary valve/seal - Carry out power steering pressure test.
^ PAS fluid delivery pressure or flow too low - Carry out power steering pressure test.
^ Steering column shaft universal joint(s) stiff or seized - Check/replace components.
^ Front hub or steering ball joints seized.
^ Steering box worn.
11. Steering varies from heavy to light when driving at a constant speed:
^ Incorrect speedometer signal - Check the speedometer circuit - Refer to the Circuit Diagrams.
^ Steering transducer cable/connection faulty or grounded - Refer to the circuit diagram.
12. Uncharacteristic steering effort/speed relationship:
^ Steering transducer circuit - Refer to the circuit diagram.
13. Steering varies from light to heavy twice per steering wheel revolution:
^ Steering column shaft universal joint(s) binding - Check/replace components.
14. Excessive kick-back through steering wheel when driven on rough terrain:
^ Excessive free-play in steering ball joints and linkage.
^ Steering box badly worn.
^ Excessive free-play in front hub bearing - Replace hub/hub bearings.
^ Front suspension bushes worn.
15. Noise emanating from the system:
^ PAS pump - Check pump retaining bolts, drive flange and pulley.
^ Noise from PAS pump when a load is applied - Check belt for condition and that belt is correctly tensioned.
^ PAS pump drive belt - Check belt and tensioner for condition and that belt is correctly tensioned.
^ Noise increases when load is applied to the system - Check system for leaks, rectify as necessary. Carry out power steering pressure test.
^ Start-up noise in extreme cold conditions - Noise should disappear as system warms up, if noise persists, carry out power steering pressure test.
^ Whining noise from system, increasing when load is applied - Check system for leaks, rectify as necessary. Carry out power steering pressure test.
^ Noise during steering gear movement - Possible water contamination of PAS fluid, drain system and refill with fresh fluid. Cavitation due to restricted PAS or fluid cooler hose(s) or pipe(s) - Replace hose(s) or pipe(s) as necessary.
16. Steering vibration:
^ Loose/worn steering ball joints.
^ Steering box bolts loose.
^ Loose/worn suspension bushes or ball joints.
^ Steering column retaining bolts loose.
^ Steering rack mounting bushes worn.
^ Excessive wear in steering column assembly.
17. Steering wheel shimmy (Vibration):
^ Road wheel imbalance.
^ Worn front suspension components, mountings, loose fixings.
^ Check/adjust steering geometry.
^ Vibration increases under light brake application - Check brake disc thickness.