Power steering systems make a significant contribution to improving the low-speed driving experience not only on high-end luxury vehicles, but also on mid-range and most base models. Moreover, hydraulic power steering systems are also fairly robust and while failures of power steering pumps do occur, sudden and/or catastrophic failures are relatively rare.
Function Of A Power Steering Pump
As the term suggests, the function of a power steering pump is to deliver pressurized fluid to the steering rack in order to decrease the amount of effort required to steer the vehicle at low road speeds. In modern designs, the amount of power assistance is modulated such that maximum assistance is delivered at low road speeds, and power assistance decreases progressively as the road speed increases. In most cases, power assistance is removed completely at road speeds above about 30 – 35 miles per hour to improve steering feedback to the driver.
In purely hydraulic power steering systems, fluid is pressurized by a belt-driven, positive displacement pump, and the pressure of the power steering fluid is therefore dependent on the engine speed. However, in practice, all power steering pumps are fitted with pressure regulating valves that both maintain the minimum required pressure/volume and prevent excessive pressure from being developed at high engine speeds.
When the pressure in the power steering system approaches or exceeds a maximum allowable threshold, the pressure overcomes the tension of a spring, which opens the pressure relief valve, thereby causing most or all of the pressurized fluid to be diverted directly back into the system reservoir. Similarly, when the steering system is idle while the engine is running (i.e. there are no steering inputs), the pressure relief valve allows the fluid to circulate from the reservoir, through the pump, and back to the reservoir.
When a steering input occurs, the fluid volume in the steering rack increases, which causes a pressure drop in the high-pressure side of the system that results in partial closure of the pressure relief valve. In this condition, some pressurized fluid is directed to the steering rack, where the effective hydraulic steering input is increased to decrease the steering effort of the driver.
How much fluid is directed into the steering rack at any given moment depends on the signal that is generated by a torque sensor (located in the steering column) that detects both whether the steering wheel is turned as well as the magnitude of the steering input.
It must be noted though that the above description applies to power steering systems in their simplest form, and not to more advanced systems like electro-hydraulic and purely electric power steering systems. Purely electrical systems use electric motors and various sensors to multiply and control steering inputs, while electro-hydraulic systems use two or more load/torque sensors, typically two electrical motors to drive a single hydraulic pump, and a microprocessor for control purposes. These types of systems can be significantly more complex and as such, fall outside the scope of this article.
Common Symptoms Of A Faulty Power Steering Pump
The symptoms of faulty power steering pumps are much the same no matter what type of vehicle you are driving, and could include any of the following:
Check Engine Light
For some vehicles, the power steering system is fitted with pressure sensors to monitor the operation of the pump. Therefore, a complete loss or serious reduction of the working pressure could cause a check engine light to illuminate. If a check engine light illuminates, you can easily find out what trouble code it is associated with using an inexpensive OBD code reader.
Loss of Steering Assistance
Mechanical failures of power steering pumps can cause a complete loss of pressure, and while this is rarely dangerous in itself so long as the driver is aware (since non-power steering functionality will still usually be available), the sudden loss of power steering assistance can require significant effort to steer the vehicle at low speeds which can surprise a driver if pressure is lost while the vehicle is in motion.
Low fluid levels, dirty or contaminated fluid, or the incorrect type of power steering fluid can cause rapid and severe mechanical wear of moving and rotating parts within a power steering pump, which typically manifests as whining, rumbling, or grinding noises in the pump. These noises will typically vary with engine speed since the pump is most often belt driven off the engine. If not addressed immediately, pump failure is likely to follow shortly thereafter.
Steering May “Stick”
Low fluid levels and some mechanical failure modes can cause intermittent pressure losses in the system, which typically manifests as points where the steering wheel “sticks” or binds when it is turned from lock-to-lock, regardless of the direction in which it is being turned. This is a significant safety concern and the vehicle should not be driven under these circumstances until a repair is completed.
Replacing A Power Steering Pump
Depending on the application, replacement procedures can vary from easy, to moderately difficult, to extremely challenging, since working space is extremely limited on some vehicles.
Note: The example steps below are intended for general informational purposes solely to help give you an idea of project difficulty and tools required. As all cars are engineered differently, repair procedures and safety hazards vary from vehicle to vehicle. To ensure that you have a vehicle specific repair procedure and an exhaustive list of potential safety hazards, we advise you reference a factory service manual for your vehicle. Similarly, referencing a repair manual such as Chilton or Haynes might serve as a less expensive alternative.
Step 1 – Make sure the engine is cold to prevent scalds and burns. Locate the power steering pump, and spend a few minutes studying the general layout of the system. It is important to locate all brackets and fasteners, some of which may be hidden behind unrelated brackets and or components. Also, use this time to remove as much fluid from the reservoir as possible to minimize spills later on. A fluid pump or a large syringe can make this happen with relative ease. Drain the power steering fluid into an oil drain pan and dispose of the old fluid in an environmentally responsible way (many oil change shops accept old power steering fluid and will recycle it safely on your behalf). If your steering pump is underneath your vehicle, you will likely need to raise it using an appropriately rated floor jack and support it using an appropriately rated set of jack stands.
Step 2 – Study the routing of the serpentine (drive) belt, and if a manual is not available, take as many pictures of the belt’s routing around pulleys and tensioning devices as it takes to give you a clear picture of how the belt fits relative to all driven components. Some belts can be extremely tricky to fit back on, so if you do not have a clear picture of how it fits, you can spend several hours trying to work it out. Taking a picture or two will give you something to reference to make sure you reinstall properly when the time comes.
Step 3 – Locate the belt tensioner, and use suitable tools and appropriate methods to remove the tension in order to remove the drive belt. DO NOT force the belt off any pulley: doing this will destroy the belt and potentially other components. Depending on the style of tensioner, this can sometimes be accomplished with a deep socket and a breaker bar. Other times, it will require a tool specific to your vehicle.
Step 4 – Take a moment to ensure that you understand your steering system. Depending on the system, you may have to take precautions to depressurize the system prior to continuing to avoid injury associated with highly pressurized fluid. Refer to a factory service manual to make sure you are aware of any safety concerns. Remove both the low and high-pressure hoses from the pump using flare nut wrenches or combination wrenches, as well as any electrical connectors if any are present. The electrical connectors can often be removed by hand, although you may require a small set of screwdrivers depending on the connector type. Remove all fasteners using a socket set, and remove the old pump from the engine.
Step 5 – Fit the new pump. Insert, fasten, and torque all fasteners in the exact reverse order of removal using a torque wrench to ensure that the fasteners are torqued to factory spec. Refit all hoses and electrical connectors.
Step 6 – Refer to the manual or the pictures you took to refit the drive belt, but make sure the belt is located correctly on all pulleys to prevent damaging the belt or other components.
Step 7 – Once you are sure the belt is fitted correctly and all hose connections are free of leaks, fill the power steering fluid reservoir up to the indicated “FULL” mark using the correct type of power steering fluid for your vehicle. Be sure to replace the cap before starting the engine. Start the engine, and turn the steering wheel from lock-to-lock SLOWLY to allow the new fluid to fill the system, topping off as necessary.
Step 8 – After adding fluid and confirming that the steering operates normally with no noises present, turn off the engine. Adjust the steering fluid level as required. Test-drive the vehicle to verify that the steering system functions correctly. If something isn’t right, stop immediately, troubleshoot, and repair as necessary.
Best Power Steering Pump Brands
Cardone subjects their new and remanufactured power steering pumps to computer-controlled real world load cycles to test and calibrate the new and remanufactured parts in their products to ensure consistently reliable performance under all possible operating conditions. Moreover, many of their units are supplied with reservoirs and caps to prevent the introduction of dirt and other contaminants in pumps during packing, shipping, and storage. Overall, A1 Cardone makes great steering pumps and we are confident that they will serve you well should you choose to install one in your vehicle.
Maval is not only one of the main suppliers of OEM power steering pumps; the company is also arguably the world’s market leader in designing, manufacturing, and testing of off-road and custom steering solutions. In fact, no matter what you drive, Maval can likely supply a steering pump solution since the company’s products hold performance approvals from most of the world’s major vehicle manufacturers. We are happy to give Maval a strong recommendation as they make good parts that will withstand the test of time.