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Diagnosing Electric Power Steering System Issues

13 Sep, 19

Diagnosing Electric Power Steering System Issues

As the automotive industry is evolving, more vehicles are shifting from the traditional hydraulic power steering systems to electric power steering (EPS). This is not to be mistaken with the electro-hydraulic system; a hybrid of both systems, where a hydraulic pump is powered by an electric motor.

So, how do EPS systems work? Here is a little summary. Different sensors detect the input from the driver (torque, speed, position) and all this information is sent to the electric control unit (ECU), which calculates the amount of assistive torque needed and applies it via the electric motor (steering assistance motor). For more detailed information on how it works, check out our article – Electric Power Steering Guide.

When it comes to diagnosing issues with EPS systems, the process is very much different than how it is with hydraulic systems. Fully electric systems mean you will be dealing with data, rather than power steering fluid or damaged pumps. Keep reading to find out how you diagnose EPS issues.

Basic EPS Diagnostics

Most electric power steering systems are able to self-diagnose any faults, with the use of diagnostic trouble codes (DTC). In the EPS system, the codes would be located within the ECU and when the time came for finding the root cause of the problem, a specialised scan tool would be used to find and decipher all the DTC’s. Unfortunately, a DTC is sometimes only the beginning of the diagnosis journey, it usually takes expert electrical diagnostic knowledge to fully figure out the issue.

Note: Sometimes a DTC is accompanied with a steering warning light.

An example of the type of DTC’s you may encounter, are:

  • ‘C-series’ Code: Suggests problems with the feedback and electrical assist part of the system.
  • ‘U-Series’ Code: Suggests a problem with information sharing between the EPS, electric control module, anti-lock braking system and other systems.

On occasions, diagnostic trouble codes can trigger fail-safe strategies in the EPS system. To elaborate, a fail-safe strategy is developed to switch the EPS system to a mode that will protect the driver and the passengers, as well as the EPS system. For example, if any sensors or other important mechanisms in the EPS system malfunctioned, the self-diagnostics would discover the issue, form a DTC for it and then switch off power-assist, leaving just manual steering.

Something else that will either decrease or turn off power-assist, is if the ECU detects that the electric motor is repeatedly providing a very large amount of torque, causing it to heat up excessively. To elaborate, if you are driving at a very slow speed or are idle, and you are continuously turning the steering wheel left or right, it’s likely the motor will overheat. To prevent this, the ECU will reduce the electric current in the motor and restrict power-assist from being applied.

Tips For Diagnosing EPS Issues

The main indication you’ll get if there is a malfunction with the electric power steering system is that the EPS light will illuminate on the dashboard. Specifically, the warning light will come on when the EPS system is off. This is when the scan of the vehicle’s diagnostic trouble codes will need to be carried out to expand your knowledge on where the issue lies. Some general issues that you may have with EPS systems are:

  • Problems With Alignment: You may encounter an issue where the electric power steering is providing more assistive torque in one direction, than the other. For example, it may be easier to turn the steering wheel to the right than left. If wheel alignment has been corrected, this issue could be due to a fault with the steering angle sensor. This will need to be re-calibrated, in order for it to give the correct position of the vehicle to the ECU, which will then provide the correct amount of assistive torque.
  • Lack Of Power-Assist: If this occurs, a DTC code could have triggered the fail-safe strategy, meaning no power-assist will be available. Therefore, this safe mode will need to be reset.

Even though there are no power steering pumps or hoses to worry about, there are other components in the electric power steering system that could malfunction. If a fault does occur in the system, they may exhibit some problems:

Steering Wheel Difficult To Turn

If turning your steering wheel to either side becomes hard, you should inspect:

  • Torque sensor
  • Tyres
  • Electric steering rack/pump/column
  • Steering column shaft
  • Steering ECU + Supply voltage
  • Vehicle Speed Sensors

Uneven Left-Right Power Steering Assist

If there seems to be an imbalance in the steering, you should inspect the:

  • Torque sensor calibration
  • Alignment of all the wheels
  • Electric steering pump/rack
  • Steering ECU

Sounds In The Steering Wheel


  • Steering gear (e.g. steering rack)
  • Steering column
  • Note: If the noise specifically sounds like squeaking, you should check the electric motor.

When Driving, The Amount Of Assistive Torque Doesn’t Decrease

From when you are stationary to when you begin driving, the assisted torque will differ based on wheel speed and steering angle. So if the amount doesn’t decrease when you start driving, you should inspect the:

  • Torque sensor
  • Electric motor
  • ECU

Electric Power Steering Specialist Near Me

Are you struggling with electric power steering issues? If so, you should book your vehicle in with us, at Power Steering Services. Whether it’s your electric power steering pump or your electric steering rack that is playing up, we can rebuild or replace them for a large variety of makes and models. In order to meet and exceed all OEM specifications, any EPS components we install in your car has been thoroughly tested under all driving conditions and we provide a lifetime warranty for each installed unit! Contact us today, either by filling in our easy online form or giving us a call on 0208 853 3343.

Tags : Electric Power-Assisted Steering, EPS System, Power Steering Specialist, Steering System, Torque Sensor.
2 thoughts on “Diagnosing Electric Power Steering System Issues
  • EPS not as smooth as previous car with hydraulic assist. Slight resistance to be overcome before steering effective. Result is oversteer and erratic progress. This is very sensitive but spoils the driving experience.

    • Hi Geoff

      Thanks for the enquiry,

      Having over-sensitive electric steering is a very common problem to have and it’s a fault we see on various makes and models. We have sent you an email requesting a bit more information about the vehicle. Please respond with the requested details and we’ll do our very best to assist you.

      Kind Regards


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