The best way to diagnose the hydraulic power steering pump failure on your Polo before ordering parts for it is to carry out a pressure test for the pump.
What a Pressure Test Involves
You will need a power steering pressure gauge test kit that can be connected to the high-pressure hose that runs between the steering pump and the rack. The majority of independent garages will hold such a test kit and they can be hired for around £30-£50 for a few days. The test kit contains a pressure gauge that shows pump output in bar or PSI.
The Idle-Speed Reading
A healthy idle speed reading on a pressure test would be between 5-10 bar. If the pressure reading is lower than this then it would be worth investigating further before proceeding with a loaded test.
The Full-Lock Pressure Check
Slowly turn the wheel to full lock and hold it for a short period of time while reading the pressure on the gauge. Pressure should increase to around 80-120 bar depending on type fitted. A sharp fall in pressure at full lock indicates a problem with the pump or relief valve.
What Low Pressure Actually Reveals
This form of failure could be described as a sticking relief valve. This type of problem is generally found within the steering pump itself and would be described as ‘internal wear’. A blocked filter or collapsed hose can also give similar symptoms to pump failure and should be checked before considering a new pump.
Checking Pressure Drop Across the Rack
To diagnose a faulty Hydraulic Pump and check the condition of your steering rack you can measure the pressure drop over the rack. The pressure has to drop significantly when going over the rack rather than at the pump to confirm failure of the steering rack. There is more on Volkswagen Polo Steering Pump at https://westernpowersteering.co.uk/vehicles/volkswagen/volkswagen-polo-steering-pump-2002-2014.
In reality, where low pressure has been found in pump pressure tests and hoses are clear, a sensible option would be to fit a replacement pump of similar design rather than try to repair an item that has clearly deteriorated through use.
