The automotive power steering system functions as a steering assist that lessens the amount of pressure applied to the steering wheel to turn and maneuver a vehicle. Hydraulic versions comprise the majority of power steering systems used in today's vehicles. A serpentine or single belt drives the power steering pump, which adds the needed pressure to turn the steering wheel easily. The causes for losing power steering during a turn involves checking the system and a few components.
Hydraulic Steering Fluid Level
The reservoir used in hydraulic power steering has an upper limit fluid capacity that must be maintained to allow maximum fluid flow and correct pressure. If the lines, reservoir or pump have too low a fluid level, air can exist in the system, which decreases the pressure. Low hydraulic fluid level stops the pump from exerting the correct pressure, thus lowering the power assist. Loss of steering ease can result in a turn in either direction, particularly at low speed or idling conditions. A buzzing noise during a turn often denotes low fluid level. Topping off the reservoir solves this problem.
Hydraulic Power Steering Drive Belts
Hydraulic power steering pumps are driven by serpentine or singular V-belts, which receive their power from the engine. If the belt slips from wear or contamination (oil or water), the pump efficiency lessens. With lessened power to the pump pulley, the steering wheel response can feel jerky or sluggish -- most prevalent at idle and low rpm, such as in a turn. Replacing or tightening the belt remedies this problem.
Hydraulic Pump Valve Blockage
Hydraulic fluid that is old, has lost its lubricating and cooling properties or is contaminated can cause an intermittent power steering loss. Dirty pressure valves inside the pump can momentarily freeze or become clogged, disallowing enough pressure to turn the steering rack gear. A sporadic jerking of the steering wheel during a low rpm, hard-over turn in tight parking or parallel parking situations is a common occurrence. A flush and change of fluid remedies this problem.
Low RPM Hard-Over Turning
If the engine idle is under manufacturer's recommended rpm specifications, or the engine is not tuned for correct performance, the power steering pump does not supply enough pressure for smooth turning. This frequently occurs during engine idle and hard-over turns during parking or very low-speed, sharp turns. The act of turning the wheel hard against the steering stops at idle and robs engine horsepower to drive the pump. This causes a sluggish or jerky response in the steering wheel, often accompanied by a howl or loud screech. Raising the engine rpm solves this problem.
Air pockets in the power steering system interrupt the flow of power steering fluid, momentarily decreasing the pump pressure. An improper system flush or a leak in the lines can introduce air, which causes a temporary blockage or open pocket in the fluid stream. The steering wheel may have a normal power-assisted response, then stop or sling back slightly. This condition primarily happens at idle and low-speed turns, but can happen at higher speeds if the air pocket is large. A power steering system fluid flush remedies this problem.
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