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 hy-brid 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).
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.
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:
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.
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:
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:
If turning your steering wheel to either side becomes hard, you should inspect:
If there seems to be an imbalance in the steering, you should inspect the:
Inspect:
Note: If the noise specifically sounds like squeaking, you should check the electric motor.
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:
