Power Steering Pump: a Detailed Description

What is a power steering pump?

A power steering pump is a component of the power steering system. To be put simply, power steering is what helps you turn the steering wheel of a vehicle with ease. Car manufacturers include power-assisted steering devices in their modern cars to reduce the stress and effort put into steering the vehicle while driving.

For power steering systems to work, a power steering pump is present to pump fluid into the steering gearbox. Learn more about power steering here.  The power steering pump is powered by the vehicle’s engine using a pulley and belt assembly.

Small ports present in the steering shaft allow high-pressure fluid to flow in and makes the act of steering the vehicle easy. Each time the steering wheel is turned, the ports open up.

power steering pump components

How does the power steering pump function?

In the early days of automobiles, steering a car took a lot of upper-body energy.Turning the wheels was literally a wrestling match between you and the vehicle’s steering system. This, therefore, was not good for some driving scenarios like slowing down to navigate sharp bends especially while driving heavy trucks.

In modern times, however, steering doesn’t require so much effort. It is as easy as moving your hands in the air. This is a result of the advent of power steering systems. Power steering uses hydraulic force to greatly reduce the amount of effort needed to turn your wheels.

hard steering

The job of the power steering pump is to pressurize the hydraulic fluid. Inside of the power steering pump lies a rotor equipped with vanes around the perimeter. As the rotor spins, it pulls power steering fluid out of the reservoir, increasing its pressure.

This pressurized fluid furthermore, travels onto the steering rack where it enables its appropriate movement. In addition, powers steering pumps contain a special pressure-relief valve to ensure that system pressure never becomes too high. Excessive pressure could easily damage the rotor or other internal components.

Let’s talk briefly about how a Power Pump Works

Power steering fluid enters the power steering pump through the inlet of the pump from the reservoir. Here it is pressurized and sent to the steering gear through the output of the pump. For the pump to become operational, the vehicle has to be turned ON. The pump, furthermore, is powered by a pulley attached to the vehicle’s accessory belt.

The fluid applies pressure to the steering gear which turns the wheels. This pressure, therefore, increases as the engine speed increases. When the engine is running at high speed, pressure builds up and it becomes higher than necessary. The excess pressure is dissipated with a pressure-relief valve.

There must also be sufficient pressure to turn the wheels at idle. As a result of this, the power steering pump becomes functional once the engine is turned ON. Click here to read more on how power steering works. Also, when the steering wheel is not being turned, the vehicle is not supposed to apply steering assist.

For efficiency, a sensor called the rotary valve senses when the wheel is turned by means of a torsion bar. Watch the video below to see how a power steering pump works.

Types of Power Steering Pump

There are three types of Power Steering Pumps. They are all similar in that they contain a rotor inside the pump housing that spins. The main difference between them is the design of the fins that move the steering fluid that is inside the pump.

Vane Pump

In the vane pump, the rotor is housed in an oval or elliptical-shaped enclosure. Inside, the vanes are fitted to the surface of the rotor resting against the housing walls as the rotor turns.

As fluid comes in through the inlet of the enclosure, it is trapped in between the rotor and vanes. This results in an increase in pressure within the pump enclosure and the fluid are pumped out at high pressure. Vane pumps are also the most common type of power steering pump used.

vane pump

Roller Pump

For the roller power steering pump, the pump is contained in an oval-shaped housing. There are wide V-shaped grooves that are cut into the side of the rotor. These grooves allow steel rollers to ride along the inside contour of the pump. When the roller power steering pump is in operation, centrifugal forces push the rollers to the oval enclosure’s outer edge.

Here they trap fluid, this is similar to the way the vanes catch the fluid in a vane pump. When the fluid is pressurized enough, it is forced out through outlets in the pump, driving the power steering system.

Roller pump

Slipper Pump

Similar to both pumps mentioned above, the slipper power steering pump is a rotor enclosed in an elliptical-shaped chamber. In this pump, there are springs that are topped with scrubber-type slippers. These are fitted into the wide slots of the rotor and the springs maintain constant pressure on the slippers. This is to keep them pressed constantly to the walls of the pump. When sufficient fluid enters the pump, pressure builds up and it is released to drive the power steering system.

Slipper pump

Symptoms of a bad power steering pump

  • The pump will leak, sometimes profusely and sometimes a little. The easier way to tell is to look at the pump where the pulley shaft goes in. Observe if dust has started to collect in a drooping pattern, in some cases you just see fluid.
  • The pump will whine, as you turn you'll hear a bad noise. It won’t be high-pitched and squealing but it will be disturbing.
  • The power steering will cut out, as the pump deteriorates it may lose pressure at low rpm (eg. while parking).
  • It will leave you with no power steering while you're doing 80mph on the freeway. Big trucks get hard to turn without it. The pump may just fail eventually at its own convenience and your inconvenience.
  • Squealing noises can happen when you start your car if your vehicle’s power steering pump is bad. They can also arise when you try to make sharp turns in your car.
  • Groaning noises are the worst noises your power steering pump can make. They will get worse and worse as your power steering pump continues to fail. If the power steering system fails from lack of fluid it can damage the whole system. This includes the steering rack and lines and requires complete replacement.

Why does my pump make whining noises?

There are a couple of reasons as to why your power steering pump is making whining noises, some of them are:


Cavitation can happen in two ways. The first is when the fluid level gets low. This allows the power steering pump to pump air into the fluid which causes the annoying buzzing noise. This is easily fixed by simply adding more fluid. However, it’s good to check for leaks, as the fluid that’s not there anymore had to go somewhere.

The second is from a return line leak. The low-pressure return line has a small vacuum on it. So if there is a leak, it will suck air into the system and cause cavitation. This can be as simple as a loose hose connection or a bad O-ring on the power steering pump. It could also be a line with a split in it. The solution is to locate the faulty connection or part and replace it.

Contaminated or worn out fluid

Power Steering Fluid, just like your motor oil is used to lubricate. If the oil gets thin, it does not lubricate the steering mechanisms and causes friction. That friction causes a humming type of noise. To fix this you must flush the entire system. You can use the same method in the first bullet point to flush it.

Bad oil

A bad  steering pump

A bad or damaged pump will not pump the fluid efficiently and will starve the pinions and gears of lubrication. This, in turn, causes friction and makes a humming or whining sound as well.

To diagnose a bad pump, make sure there is no air in the system as this could also cause noise. If the noise continues to sound and you are sure there is no air, then your pump is bad. Fix an appointment with an auto mechanic to get the power steering pump changed. To read more on causes of power steering whining noise click here

Fixing a power steering pump with a whining noise

To fix a bad power steering pump, you first need to figure out what's going on with the pump. First allow the engine to go cold, go ahead and pop the hood, and check the power steering pump fluid. It will be clearly marked and will probably have "power steering" written on it.

Look to see if there is fluid in there. Proceed to check the level using the provided dipstick on the cap, if it is low top it off. Make sure you are on a level surface when doing this. But if there is fluid, then look at the color and consistency of the fluid. If you notice abnormalities like discoloration or grittiness, change the power steering fluid with brand new fluid and a conditioner.

How to Change the Fluid

To change the fluid, go get a disposable turkey baster, a syringe, or something similar. This will allow you to put it in the power steering fluid reservoir and suck it out.

Extract all the old fluid and replace it with brand new fluid, adding the conditioner with the power steering fluid. Make sure the fluid is up to the level that is correct for your car. If you're not sure, remember that the correct fluid amount can be found in the user manual or online.

After you have done this, go ahead and start up the car and move the steering wheel back and forth. The whine should be instantly gone and the power steering pumps are good as new. For the next few days, check the power steering fluid level of the car. Make sure that each time you do it the vehicle is cold and not driven.

This is to make sure that you aren’t losing any fluid. It will help you discover any fluid loss or leaks before your pump goes bad. If the whining doesn’t stop or gets louder, the pump might be experiencing internal component failure or seal failure. Add a stop seal fluid additive and if the noise reduces, there is a faulty seal. However, if all these don’t work, consider getting a new power steering pump.

Watch this to hear what a bad power steering pump sounds like

Is driving with a bad steering pump bad?

Driving a vehicle with a bad power steering pump is dangerous if it’s hard to steer or stop steering unexpectedly. A leaking power steering pump can cause a fire. A dry pump will get damaged and possibly lock up or cause the drive belt damage and lose other vehicle functions. The alternator and water pump, if driven by the accessory belt, will no longer be driven. This can possibly leave you in perilous situations.

What should I do when my pump fails?

If you notice your power steering is going bad, stop driving until it is fixed. You could diagnose the problem using the procedure listed above. But in worse situations an outright swap of the power steering pump.

oil pump failure

What does it cost to change a faulty steering pump?

A lot of factors affect the replacement of a faulty pump. One is the type of car you drive, the make and model also and if it is an older model. A mechanic may have a more difficult time finding the parts they need. Some of these parts could take a while to get because they are not as common as the ones for newer cars. If this happens, you will be charged more money for this replacement.

The second is where you live. The cost of living is different in every city, which allows repair shops to charge different prices for replacements. The general guide for most pump replacements is around $200 to $350. However, due to the factors listed above it could vary slightly. This price does include the cost of the part as well as the cost of labor. For a more detailed cost report click here

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