How does it work?
The pump itself draws in fluid from a return line and pressurizes it. This system has to make enough pressure to turn the wheels at idle, requiring a valve to control pressure when the engine is running at higher speeds.
This fluid is directed into a valve body around the steering shaft. If the wheel is straight, the incoming fluid passes around the body into the return lines. However, once the wheel starts turning, it blocks off some of the passages, causing the fluid to exert rotational pressure. It’s this application of hydraulic power that makes the vehicle easier to steer.
What can go wrong with power steering?
If there isn’t enough fluid in the system, there is air in the system, there is a leak in the system or there are contaminants in the fluid, there won’t be enough fluid pressure to power the system. Blockages can reduce pressure at idle, making the vehicle difficult to turn at low speeds yet behave normally at street and highway speeds.
If the pump or drive belt fails, turning the steering wheel operates the steering rack manually while also pushing fluid through the lines. This makes it extremely difficult to steer. If either part is near failure, there will be noise when turning, particularly when making sharp turns.
How can these problems be addressed?
The power steering pump should be located next to the engine, with a clearly marked reservoir attached to it. There should be a dipstick on the inside of the cap: Some vehicle have “hot” and “cold” markings, but readings will be more accurate if the fluid level is checked while the engine is cold. The type of fluid required should be marked on the top of the cap. Old fluid can be removed using a syringe. Fluid that is shiny or has metal filings is a sure sign that the pump is near failure.
In some vehicles, it’s normal to hear some noise when the wheel is turned all the way to full lock, but constant noise is usually due to a slipping drive belt. Some flexing of the belt is OK: A tight belt can pull on the drive pulley, causing rapid bearing wear. If the belt is in good shape and properly tensioned, the problem is usually worn bearings.
Leaks usually occur at the hoses or a kinked line: Follow the path of these parts from the pump to the steering rack and look for any obvious leaks. Leaks from the pump are less common, but are usually caused by holes in sheet metal fluid reservoirs or a bad seal on a plastic reservoir.