2010 Mercury Milan Electric Power Steering

Let's dive into the Electric Power Steering (EPS) system found in the 2010 Mercury Milan. While the Milan primarily used a traditional hydraulic power steering system, *some* models, especially those equipped with the hybrid powertrain, incorporated EPS. This article will focus specifically on the workings of that EPS system and how it differs from its hydraulic counterpart. We'll cover the components, the control logic, potential problems, and some basic troubleshooting tips relevant to the DIY mechanic.

EPS vs. Hydraulic Power Steering: A Key Difference

Before we get into the specifics of the Milan's EPS, it's crucial to understand the fundamental difference between it and hydraulic power steering. Hydraulic systems use an engine-driven pump to pressurize hydraulic fluid, which then assists the driver in turning the wheels. This system is constantly drawing power from the engine, even when you're driving straight. EPS, on the other hand, uses an electric motor to provide steering assistance. The beauty of EPS lies in its efficiency: it only draws power when needed, leading to improved fuel economy. Furthermore, EPS systems can be more easily integrated with advanced driver-assistance systems (ADAS) like lane keeping assist.

Components of the 2010 Mercury Milan EPS System

The EPS system in the 2010 Milan (when equipped) primarily comprises the following components:

Torque Sensor: Located on the steering shaft, the torque sensor measures the amount of force the driver is applying to the steering wheel. This sensor is *critical* because it's the primary input for determining how much assist the EPS motor should provide.
Electric Power Steering (EPS) Motor: This motor provides the actual steering assistance. It's typically a brushless DC motor known for its efficiency and durability. The motor's output is geared to the steering system to amplify the assistance.
Electric Power Steering Control Module (EPSCM): The brain of the system, the EPSCM receives signals from the torque sensor, vehicle speed sensor (VSS), and other sensors. Based on this data, it calculates the appropriate amount of assist and controls the EPS motor accordingly. The EPSCM also monitors the system for faults and stores diagnostic trouble codes (DTCs).
Vehicle Speed Sensor (VSS): The EPSCM uses the vehicle speed signal to adjust the level of steering assist. Generally, more assist is provided at lower speeds (for easier parking) and less assist at higher speeds (for greater stability).
Steering Gear: This is the mechanical link between the steering wheel and the wheels of the car. In some EPS systems, the EPS motor directly assists the steering gear. In others, it assists the steering column. The Milan's EPS typically assists the steering column.
Wiring Harness and Connectors: These are the lifelines of the system, carrying power and signals between the various components. Corrosion and loose connections are common causes of EPS problems.

How the EPS System Works

The process of steering assistance with EPS is as follows:

The driver applies force to the steering wheel.
The torque sensor detects the amount of force and sends a signal to the EPSCM.
The VSS also sends a signal to the EPSCM indicating the vehicle's speed.
The EPSCM analyzes the signals from the torque sensor, VSS, and other sensors.
Based on this analysis, the EPSCM determines the appropriate amount of assist.
The EPSCM sends a signal to the EPS motor, instructing it to provide the required amount of assist.
The EPS motor actuates, providing mechanical assistance to the steering system, making it easier for the driver to turn the wheels.

Troubleshooting Common EPS Problems

EPS systems are generally reliable, but they can experience problems. Here are some common issues and potential troubleshooting steps:

Loss of Power Steering Assist

This is the most common complaint. If you experience a sudden loss of power steering assist, the first thing to check is the EPS warning light on the instrument panel. If the light is on, it indicates a fault in the system. Connect a scan tool to the OBD-II port and retrieve the diagnostic trouble codes (DTCs). These codes will provide clues as to the source of the problem. Some common causes include:

Faulty Torque Sensor: If the torque sensor is malfunctioning, it may send incorrect signals to the EPSCM, resulting in a loss of assist. DTCs related to the torque sensor are common in this scenario. Testing the sensor requires specialized equipment and technical knowledge, so a professional diagnosis may be necessary.
Faulty EPS Motor: The EPS motor itself can fail, preventing it from providing assistance. DTCs will usually indicate a motor failure. Replacing the EPS motor often involves removing the steering column, so it's a relatively involved repair.
Faulty EPSCM: While less common, the EPSCM itself can fail. DTCs may indicate an internal EPSCM fault. Replacing the EPSCM often requires programming the new module to match the vehicle's VIN.
Low System Voltage: EPS systems require a stable voltage supply to operate correctly. A weak battery or a faulty alternator can cause the EPS to malfunction. Check the battery voltage and the alternator output.
Wiring Problems: Damaged wiring or loose connections can disrupt communication between the various components. Inspect the wiring harness and connectors for any signs of damage or corrosion. Pay close attention to the ground connections, as a poor ground can cause all sorts of electrical problems.

Intermittent Power Steering Assist

Sometimes, the power steering assist may work intermittently, cutting in and out randomly. This can be caused by:

Loose Connections: Check all connectors in the EPS system for looseness and corrosion. Vibration can cause connections to loosen over time, leading to intermittent problems.
Faulty Sensors: A sensor that is on the verge of failing may produce intermittent readings, causing the EPSCM to malfunction.
Overheating: In rare cases, the EPS motor can overheat, especially during prolonged periods of heavy use (e.g., aggressive driving). This can cause the motor to temporarily shut down.

No Power Steering Assist at All

If there is absolutely no power steering assist, even at low speeds, the problem is likely more severe. Consider these possibilities:

Blown Fuse or Relay: Check the fuses and relays associated with the EPS system. A blown fuse can completely disable the system. Consult the owner's manual or a wiring diagram to locate the correct fuse and relay.
Complete EPSCM Failure: A complete failure of the EPSCM will render the system inoperative.
Mechanical Binding: While less likely in an EPS system, mechanical binding in the steering gear can make it extremely difficult to turn the wheels.

Diagnostic Trouble Codes (DTCs)

Understanding DTCs is crucial for troubleshooting EPS problems. Here are some common DTCs associated with EPS systems and their possible meanings:

Note: This is not an exhaustive list, and specific DTC definitions may vary depending on the diagnostic tool used. Always refer to the vehicle's service manual for accurate DTC information.

C1513: Torque Sensor Signal Malfunction
C1517: EPS Motor Malfunction
C1521: EPSCM Malfunction
U0100: Lost Communication With ECM/PCM
U0121: Lost Communication With ABS Control Module

Safety Precautions

Working on the steering system can be dangerous if proper precautions are not taken. Always disconnect the negative battery cable before working on any electrical components. Be careful when working around the steering column, as it contains airbags and other safety devices. If you are not comfortable working on the steering system, it is best to take your vehicle to a qualified mechanic.

Conclusion

The Electric Power Steering system in the 2010 Mercury Milan is a sophisticated system that provides efficient and effective steering assistance. Understanding the components, operation, and common problems can help you troubleshoot issues and keep your steering system in top condition. Always refer to the vehicle's service manual for specific diagnostic and repair procedures. Remember, when in doubt, consult a qualified mechanic. Safe and reliable steering is paramount!