Key Insight: Electric Power Steering (EPS) failure is a serious issue that can make a vehicle difficult to control. The causes vary widely but can generally be categorized into several key areas.
Unlike traditional hydraulic systems, EPS uses an electric motor to provide steering assistance. This means failures are typically related to sensors, electronics, or the motor itself.
Here is a detailed analysis of the most common causes of electric power steering failure.
1. Sensor Failures (The System's "Eyes")
The EPS system relies on data from multiple sensors to determine how much assistance to provide.
Torque Sensor
This is the most critical sensor. It's mounted on the steering column and measures the force (torque) the driver applies to the steering wheel. If it fails or provides incorrect data, the control module doesn't know how much assistance to provide.
Typical symptoms: Intermittent loss of power assistance, steering feels "notchy" or "jumpy," or suddenly becomes very heavy or very light.
Steering Angle Sensor
This sensor tells the control module the position and rotation rate of the steering wheel. It's also crucial for stability control systems (ESC/ESP). Its failure can confuse the EPS computer, causing abnormal power assistance.
2. Electric Power Steering Motor Failure (The System's "Muscle")
This is the physical component that provides steering force.
- Brush/Commutator Wear: In traditional brushed motors, brushes wear over time. Once they become too short, contact is lost and the motor stops working. This typically happens gradually.
- Internal Bearing Failure: Motor bearings can wear out, producing noise (grinding, humming) and eventually causing the motor to seize.
- Electrical Failure: Short circuits or breaks in the motor windings will cause immediate and complete failure.
3. Electronic Control Unit (ECU) Failure (The System's "Brain")
The EPS module is a computer that processes data from sensors and commands the motor.
- Internal Component Failure: Like any computer, capacitors, transistors, or microchips on the circuit board can fail due to heat, vibration, or age. This usually causes sudden and complete loss of power steering.
- Corrosion or Water Damage: If water enters the control module (usually located in the engine bay or under the dashboard), it can cause short circuits and destroy the circuitry.
4. Power Supply and Connection Issues
The system requires stable, clean power to function properly.
- Low System Voltage: A weak or dying battery, or alternator failure, may cause the EPS system to shut down to protect other vehicle electronics, or because it doesn't have enough operating voltage. The problem may be intermittent, coming and going with electrical load changes.
- Poor Ground Connection: Corroded or loose ground wires are a very common cause of abnormal EPS behavior. The system is sensitive to voltage fluctuations, and poor grounding can cause various strange symptoms.
- Loose or Corroded Connectors/Harnesses: Vibration can loosen connectors, and exposure to the elements can cause corrosion, resulting in intermittent signals to sensors or the motor.
5. Physical Damage
- Steering Gear Failure: Although the steering gear is a mechanical component, if it's internally damaged or seized, it can place excessive load on the EPS motor. The system may detect this overload and shut down to protect the motor.
- Accident Damage: A collision can physically damage sensors, wiring harnesses, or the motor housing.
6. Software/Calibration Issues
After disconnecting the battery or performing certain repairs, the EPS module may need to be recalibrated. Otherwise, steering may feel abnormal or not work correctly.
Common Symptoms Before Failure
- EPS Warning Light: The most obvious sign—a steering wheel icon appears on the dashboard, usually with an exclamation mark.
- Sudden Loss of Power Assistance: Steering becomes extremely heavy and difficult to turn, especially at low speeds.
- Intermittent Power Assistance: During driving, power assistance comes and goes.
- Notchy or Sticky Steering: Steering isn't smooth, feeling like it's catching or jumping.
- Unusual Noises: Grinding, humming, or clicking sounds from the steering column or steering gear when turning.
Common Problem Severity
| Failure Cause | Frequency | Typical Symptoms | Severity |
|---|---|---|---|
| Torque Sensor Failure | Very Common | Intermittent/notchy steering, warning light on | High - Requires Repair |
| Low Battery/Voltage | Common | Intermittent failure, especially noticeable at idle | Medium - Check Electrical System First |
| EPS Motor Brush Wear | Common (on older vehicles) | Gradual loss of power, works when cold, fails when hot | High - Motor Repair/Replacement Needed |
| Poor Ground Connection | Very Common | Erratic behavior, usually intermittent | Low/Medium - Easy/Inexpensive to Fix |
| ECU (Control Module) Failure | Less Common | Sudden complete loss of power assistance | High - ECU Itself is Expensive |
What to Do If EPS Fails
- Stay Calm. The vehicle can still be steered mechanically, but it requires much more effort, especially at low speeds.
- Drive Safely. Pull over to a safe location as soon as possible. Turn on your hazard warning lights.
- Check Basic Items. If safe, check for obvious issues like loose connections or severely corroded battery terminals. Sometimes, disconnecting and reconnecting the battery can reset the system (but this may not be a permanent fix). Note: This may clear your radio presets.
- Get Diagnostic Testing. The most critical step is to have a professional technician scan the vehicle's computer, especially the EPS module, to read fault codes. This will directly point to the faulty sensor or component, saving diagnostic time and costs. Do not start replacing expensive parts like the steering gear without proper diagnosis.
Conclusion
While EPS systems are generally very reliable, their failures are often related to electronics and sensors rather than mechanical wear. Proper diagnosis is key to effective and cost-efficient repairs.
Frequently Asked Questions
Yes, but with caution. The vehicle can still be steered mechanically, but it will require significantly more effort, especially at low speeds and when parking. It's recommended to have the issue diagnosed and repaired as soon as possible for safety reasons.
Repair costs vary widely depending on the cause. Simple fixes like addressing poor ground connections may cost very little, while replacing the EPS motor or control module can cost $500-$1500 or more, including labor. Proper diagnosis is essential to avoid unnecessary part replacements.
Intermittent EPS failure is often related to electrical issues like poor connections, corroded grounds, or a failing battery/alternator. It can also indicate a sensor that's beginning to fail or an EPS motor with worn brushes that lose contact when hot.
Yes, absolutely. The EPS system requires stable voltage to function properly. A weak battery or failing alternator can cause the system to shut down intermittently, especially when electrical load is high (when using headlights, AC, etc.).
It depends on your vehicle's age, mileage, and warranty terms. Many manufacturers offer extended coverage for EPS components due to their critical safety nature. Check your warranty documentation or contact your dealership to determine if your specific issue is covered.