The power steering pump makes it easy to manoeuvre your car with little effort. A serpentine belt connects the pump to the crankshaft, moving hydraulic fluid through a closed system. When a car gets hard to steer, or when strange growls and whines emanate from under the hood, it might be time to replace the power steering pump. Other problems, such as low fluid or maladjusted belts, can also masquerade as a bad pump. An inspection or a pressure test can be used to diagnose a bad power steering pump.
Listen for a squealing noise with the hood open and the engine running. Popular Mechanics likens this noise to a "moose in heat." It might sound similar to the whine your pump can make when cranking the steering wheel all the way to one side, but this squealing can happen with the steering wheel in any position. Check the tension on the serpentine belt to make sure you aren't hearing the belt squealing instead.
Check the fluid level in the power steering pump. If the fluid is low, there is likely a leak somewhere. Look underneath the car. The red, translucent colour of power steering fluid makes it easy to distinguish from dark grease or the golden tinge of engine oil. Low fluid can cause poor pump performance and can also burn out the pump.
Inspect the power steering lines for leaks, cracks or clogs. If these are faulty, they will keep the pump from receiving enough fluid. Similar to a power steering pump failure, steering might be difficult and your pump might be groaning or whining.
Test the fluid pressure on your power steering pump to confirm its failure. Turn off the engine, and unhook the pressure line from the power steering pump. Insert the pressure gauge in between the pressure line and the pump, with the gauge side facing the pump.
Turn on the engine. Crank the steering wheel all the way in one direction. Repeat this three times to remove any air from the lines that will cause false readings on the test.
Check the pressure at 1,000rpm. Rev the engine to 3,000rpm, and check the pressure again. Subtract the pressure difference, and compare it with the suggested pressure difference of your make and model vehicle.
Turn the steering wheel one direction until it stops. Check the power steering pump pressure. Evaluate this amount against the suggested pressure for your vehicle.
Power steering pump pressure tests might vary by product and by vehicle. Always follow the specific directions included with the pressure test.