Electromechanical power steering: design, malfunctions and repairs

What is electromechanical power steering and how does it work?

Electromechanical power steering (EPS) is a modern alternative to hydraulic and electro-hydraulic systems that combines simplicity of design and high efficiency. Unlike traditional hydraulic booster (power steering), where the force is created due to fluid pressure, the EUR uses an electric motor directly connected to the steering mechanism. This allows driver assistance to be precisely dosed depending on driving speed, steering angle and even driving style.

The main advantage of the EUR is energy efficiency. The system is activated only when the steering wheel is turned, while the power steering works constantly, taking power away from the engine. In addition, the electromechanical amplifier is more compact, lighter and does not require maintenance (there is no need to check the fluid level or replace seals). However, it also has weaknesses: for example, if the electronics fail, the steering wheel becomes extremely heavy, while the power steering retains minimal functionality even if the pump belt breaks.

Today, ESD is installed on most budget and mid-size cars - from Lada Vesta and Kia Rio up to Volkswagen Golf and Toyota Corolla. The system is especially popular in hybrid and electric vehicles, where energy savings are critical. But like any electronic component, the amplifier requires attention: ignoring the first signs of a malfunction can lead to expensive repairs or even an emergency.

Electromechanical power steering device

Structurally, the EUR consists of several key components, each of which plays its own role:

• 🔧 Electric motor - the core of the system that converts electrical energy into mechanical force. This is usually a brushless DC motor with high efficiency.
• 📊 Control unit (ECU) — the “brain” of the amplifier, analyzing data from sensors and regulating engine operation. In modern systems, the ECU is integrated with CAN bus car.
• 🔄 Gearbox — transmits force from the engine to the steering mechanism. The most commonly used are worm or planetary gears.
• 📱 Sensors:
  • Torque sensor — measures the force applied by the driver to the steering wheel.
  • Angle sensor — determines the position of the steering wheel.
  • Speed sensor — adjusts the assistance level depending on the vehicle speed.

Depending on the engine location, there are three types of electric power steering:

1. Columned — the engine is installed on the steering column (for example, in Renault Logan or Hyundai Solaris). Compact but limited in power.
2. Rack and pinion — the engine is integrated into the steering rack (found on Ford Focus or Skoda Octavia). Provides clearer feedback.
3. Spindle — the motor is connected to the rack through a separate drive (less often, for example, in some models BMW). The most reliable, but also the most expensive to repair.

Advantages and disadvantages of electric power steering compared to power steering and electric power steering

To understand why manufacturers are switching to electromechanical amplifiers en masse, it is enough to compare them with alternative systems. Below are the key pros and cons of each type.

The main trump card of the EUR is adaptability. The system can automatically reduce force at high speed (for stability) or increase it when parking. In some premium cars (for example, Audi or Mercedes-Benz) the amplifier even takes into account crosswinds or road slopes. However, there is also a downside: if the electronics fail, the steering wheel becomes not just heavy, but practically motionless - unlike the power steering, where a mechanical connection is maintained.

⚠️ Attention: If, after starting the engine, the power steering icon (yellow steering wheel with an exclamation mark) lights up on the instrument panel, this means the power steering is faulty. In this case It is not recommended to continue driving - The steering can lock at any time.

Signs of malfunctions of the electromechanical power steering

The EUR is a reliable system, but it is not immune to breakdowns. The first symptoms of problems are often ignored, which leads to worsening of the problem. Let's look at the most common signs:

• 🔴 Heavy steering — the turning effort has increased sharply, especially at low speed. Cause: engine failure, power supply interruption or torque sensor failure.
• 🔄 The steering wheel “wedges” — there are jerks or delays when turning. Culprits: gearbox wear, gear damage or problems with the control unit.
• 🔊 Extraneous sounds - creaking, humming or knocking when turning the steering wheel. Most often associated with wear of the engine bearings or play in the gearbox.
• ⚡ Spontaneous turns — the steering wheel “steers” to the side without the driver’s participation. A dangerous symptom indicating a malfunction in the angle sensor or control unit.
• 🚨 Errors on the dashboard — the power steering icon lights up (the error code can be read by a scanner, for example, ELM327).

Especially insidious intermittent faultswhen symptoms come and go. For example, the steering wheel may “stick” only when it’s cold or after driving over uneven surfaces. This is often due to oxidation of contacts or overheating of the electronics. In such cases, diagnosis becomes more difficult and may require checking with an oscilloscope or a test bench.

Diagnosis of EUR faults: step-by-step instructions

Before taking your car to a service center, you can carry out preliminary diagnostics yourself. To do this you will need a multimeter, an error scanner (for example, Launch CReader) and basic electrical skills.

1. Check the power steering fuse (usually located in the block under the hood or in the passenger compartment)

2. Inspect the connectors on the control unit and engine (oxidation, poor contact)

3. Read errors with the scanner (codes like C1011 or B1422 point out the problem)

4. Check the voltage at the engine terminals (should be 12 V when the ignition is on)

5. Visually inspect the gearbox for play or lubricant leaks-->

If the scanner produces errors, decipher them using the manual of the specific model. For example:

• C1010 — torque sensor malfunction.
• C1023 — open circuit of the motor power supply.
• B1422 - failure in the control unit.

For a more in-depth diagnosis you may need:

• Check the resistance of the motor windings (should be within 0.5–2 Ohms).
• Test the steering angle sensor (applying 5 V to the signal wire should produce a varying voltage when the steering wheel is rotated).
• Checking the grounding circuit (poor grounding is a common cause of ESD “glitches”).

⚠️ Attention: If during diagnostics you find that the EUR motor consumes more current 10 A in rest mode, this indicates turn-to-turn short circuit. Further use may result in a fire in the wiring!

Repair and replacement of electromechanical power steering

Depending on the nature of the malfunction, EUR repair can range from simply replacing a fuse to a complete overhaul of the system. Considered scenarios:

1. Replacing the fuse or relay

If your amplifier suddenly stops working, first check the fuse (usually 30–50 A, location is indicated in the manual). On some models (for example, Chevrolet Cruze) a separate EUR relay is also installed - its contacts may oxidize.

2. Electric motor repair

If the engine hums but does not turn, the problem may be:

• Worn out brush units (in brushed motors).
• Damaged bearings (requires disassembly and replacement).
• Winding breakage (diagnosed with a multimeter).

In most cases, the engine is not repaired, but replaced with a new or used one. Cost of a new motor for Lada Granta - about 15–20 thousand rubles, for Toyota RAV4 - up to 50 thousand rubles.

3. Replacing the control unit

If the ECU "burns out" (for example, due to a power surge), it will have to be replaced. Important: the block must be flashed for a specific car model! Required after replacement adaptation through diagnostic equipment.

4. Gearbox repair

Play or knocking in the gearbox can be eliminated by replacing worn gears or bearings. In column-mounted EUR (for example, on Renault Duster) the worm pair often wears out - it can be replaced separately.

Average cost of EUR repair in service:

⚠️ Attention: When replacing the EUR with a used unit, be sure to check it on a bench! Used amplifiers are often sold with hidden defects (for example, a worn gearbox), which will appear after 1–2 thousand km.

Prevention and care of electric power steering: how to extend service life

Electromechanical power steering does not require regular maintenance, but a few simple rules will help avoid premature breakdowns:

• 🚗 Avoid holding the steering wheel in the extreme position for long periods of time (more than 5 seconds). This leads to overheating of the engine.
• ⚡ Monitor the on-board voltage. Jumps (for example, due to a faulty generator) can damage the control unit.
• 🛣️ Minimize driving over strong bumps. Shocks are transmitted to the gearbox, accelerating wear.
• 🔧 Check the EUR fastening regularly. Play in the fastening points leads to vibrations and premature wear.
• 💧 Do not wash the engine and control unit with high pressure. Water ingress is a common cause of contact corrosion.

Pay special attention winter operation. At low temperatures, the lubricant in the gearbox thickens, which increases the load on the engine. If your steering wheel feels heavy after a cold night, don't panic—this is normal. However, if the symptom persists after warming up, check the condition of the gearbox.

FAQ: Frequently asked questions about electromechanical power steering

1. Disconnect the negative terminal of the battery.
2. Press the brake pedal and hold for 30 seconds (discharges the capacitors in the ECU).
3. Reconnect the terminal and start the engine.