Dec 30, 2021

HPS pump failures

How to check the hydraulic power steering pump. The symptoms of HPS failures.

The malfunction of a hydraulic power steering pump (HPS) not only makes the driving comfort lower but also impacts a car safety on the road. The design of hydraulic power steering system is quite simple, and you can fix it without much effort, even in your private garage. If you know the reasons of HPS pump failures, you would manage to avoid an expensive repair.

The common HPS pump failures are as follows:

  • wear and damage of pressure control valve;
  • pump leakage due to the wear and damages of seals;
  • wear of bearings;
  • wear of the thrust plate, or wear of the stator inner side.

The pressure control valve fails if the oil hasn’t been changed in the system for a long time or the pump has overheated due to the longtime holding of the steering wheel in the extreme position. This failure becomes apparent through the increasing of steering wheel turning force when the engine is warm. Moreover, you would hear the pump hum.

The pump leakage can appear due to the wear or damage of seals and gaskets. Besides, the level of the operative liquid in the pump tank. This failure is a result of either the pump shaft corrosion or improper pump mounting

The bearings wear because of uncommon impacts and the abnormal loads like the shocks and vibrations – due to the wrong mounting of the pump (there’s looseness), for example.

The continuous pump hum and extra steering wheel turning force warn that the required pressure cannot be generated by the pump.  Commonly, it’s a result of the worn thrust plate or uneven wear of the stator inner side.

Mostly, HPS pumps fail because HPS system is not maintained in time. To avoid the troubles, follow the recommendations:

  • change the oil in hydraulic power steering system every 15.000 km of run distance;
  • when changing the oil, flush the hydraulic system to remove the old oil and the wear products completely;
  • use the relevant oil of high quality;
  • in winter, warm the car a bit longer so the hydraulic power steering system got warm properly;
  • do not hold the steering wheel in the extreme position.

How to check the hydraulic power steering pump?

The accurate diagnostics of HPS pump requires the special professional equipment. For example, by the tester MS611, you can test HPS pump without its removal from a car, or you can use MS603N for the same purpose.

The equipment can reveal the pump malfunctions and identify the necessity of its removal for repair.

MS604 – the test bench for the diagnostics of the dismounted pump, it checks the technical condition of the unit and identifies the failure type. Moreover, the test bench controls the repair quality to be sure that all is fixed. 

Learn more about the professional equipment for the diagnostics and the repair of steering units  on our website, or contact us.


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