ASE A4 Suspension and SteeringSteering System Diagnosis and RepairHard
A vehicle with hydraulic power steering is exhibiting a persistent humming or groaning noise that is most prominent when the steering wheel is held at full lock, and the power steering fluid appears foamy. The technician has confirmed the fluid level is correct. What is the MOST likely cause of these symptoms?
- AA worn power steering pump flow control valve.
- BAir ingestion into the power steering system.
- CA restricted power steering pressure line.
- DExcessive internal wear in the steering gear's rotary valve.
Show answer & explanationAnswer & explanation
Correct answer: B. Air ingestion into the power steering system.
A humming/groaning noise, especially at full lock, combined with foamy fluid, is a classic indication of air in the power steering system. Air can enter through various points like a leaking O-ring, loose hose clamp, or a pinhole leak in a return line. When held at full lock, the pump works harder, exacerbating the noise and churning the air into foam.
Why the other options are wrong
- A. A worn flow control valve would cause heavy or inconsistent steering, possibly with a groan, but not typically foamy fluid or a noise specific to full lock.
- C. A restricted pressure line would cause very heavy steering and potentially high-pressure leaks, but not foamy fluid or a humming noise (it would be more of a strain/whine).
- D. Excessive wear in the steering gear's rotary valve would primarily cause heavy steering or a 'dead spot,' not foamy fluid or a specific full-lock noise.
Power Steering Air Ingestion
Air ingestion into a hydraulic power steering system causes a humming/groaning noise (worse at full lock) and foamy power steering fluid. It results from leaks allowing air to enter, often at the return side or reservoir.
- Foamy fluid is key indicator.
- Noise worse at full lock due to cavitation.
- Check for leaks at hoses, O-rings, reservoir.
Memory trick: Foamy fluid hums, it's sucking in air.