Steering Angle Sensors and Variable Ratio Steering: What You Need to Know
A car’s steering system is a complex arrangement of mechanical and electronic components that allow the driver to control the direction of the vehicle. Its primary purpose is to convert the rotational motion of the steering wheel into the left-right motion of the front wheels, enabling the car to turn and navigate.
The steering system is an essential safety feature – without it, cars would be impossible to control. It must provide precise and responsive handling, while also filtering out road vibrations and bumps from reaching the driver’s hands. Modern steering systems are carefully tuned to balance responsiveness and stability at various speeds.
Key Components of a Steering System
While designs vary, most car steering systems consist of the following core components:
- Steering wheel – The driver interface for controlling direction. Connected to the steering column.
- Steering column – Connects the steering wheel to the rack and pinion or steering box. Houses the ignition switch and steering lock.
- Steering gear (rack and pinion or steering box) – Converts the rotational motion of the steering column into the linear motion needed to turn the wheels. The most common types are rack and pinion and recirculating ball steering boxes.
- Tie rods – Connect the steering gear to the steering knuckles on the wheels.
- Steering knuckles – Attach the wheels to the suspension and pivot when pushed/pulled by the tie rods to turn the wheels.
- Power steering pump and hydraulic lines (hydraulic power steering) – Provides hydraulic pressure to assist with steering effort. Consists of a pump driven by the engine via a belt, a fluid reservoir, and high pressure lines.
- Electric motor and control module (electric power steering) – Uses an electric motor mounted on the steering column or rack to provide steering assist. Controlled by a dedicated module using data from steering torque and angle sensors.
When the driver turns the steering wheel, this rotation is transferred down the steering column to the steering gear. The steering gear, either a rack and pinion or recirculating ball type, converts the steering wheel’s rotation into the linear motion needed to pivot the wheels.
The tie rods, connected to both ends of the steering gear, push or pull the steering knuckles which pivot the front wheels in the desired direction. The geometry of the steering linkage, especially the angles of the tie rods, is carefully designed to optimize handling characteristics.
Power steering, either hydraulic or electric, greatly reduces the physical effort needed to turn the steering wheel, especially at low speeds. Hydraulic systems use a pump to generate high fluid pressure which assists the steering gear, while electric systems use a motor to provide assist torque directly.
Steering Feel and Feedback
An often overlooked but critical aspect of steering design is the feedback and feel it provides to the driver. A good steering system should communicate useful information about road conditions and tire grip to help the driver control the car, especially near the limits of traction.
This is achieved through careful tuning of the steering geometry, power assist levels, and damping characteristics. Too much power assist and isolation will result in numb, uncommunicative steering, while too little will make the car tiring to drive. Getting this balance right is crucial.
Steering Angle Sensor
Modern cars with stability control systems use a steering angle sensor to detect the position and rate of rotation of the steering wheel. This sensor is typically located in the steering column and consists of an optical or magnetic encoder.
The steering angle sensor provides key data to the stability control module, which compares the steering inputs to the actual yaw rate and lateral acceleration of the car. If the system detects the car is not responding as expected, it can selectively brake individual wheels to help correct the trajectory.
Steering angle sensor faults are a common issue that can cause warning lights and loss of stability control features. Resetting or recalibrating the sensor often requires specialized tools and procedures, which we’ll cover later in this article.
Variable Ratio Steering
Some high-performance cars use variable ratio steering racks to optimize steering response in different situations. With a variable ratio rack, the steering ratio (degrees of steering wheel rotation per degree of wheel pivot) changes depending on the steering angle.
Near the center position, the ratio is slower, providing stability at high speeds and reducing steering sensitivity. As the wheel is turned further, the ratio quickens, allowing rapid maneuvering with less arm twirling when parking or cornering hard.
Variable ratio steering can be achieved mechanically with racks that have different tooth pitches for the center and ends, or electronically by altering the power steering assist curve.
Four Wheel Steering
A small number of cars, usually high-end sports models, incorporate rear wheel steering to enhance maneuverability. At low speeds, the rear wheels turn in the opposite direction of the fronts, virtually shortening the wheelbase and enabling tighter turns. At higher speeds, the rears turn in phase with the fronts for more stable lane changes.
Rear steering is achieved with a separate steering rack or actuators on the rear suspension links, controlled electronically based on speed, yaw rate, and steering angle data. While effective, the added cost and complexity has limited the use of four wheel steering in mainstream vehicles.
Steering System Maintenance
Proper maintenance is essential to ensure safe and reliable operation of any steering system. Some key areas to monitor are:
- Power steering fluid level and condition – Low fluid can cause hard steering or damage the pump. Dirty or contaminated fluid can clog lines and valves.
- Steering linkage and ball joints – Wear in tie rod ends or ball joints can cause loose, imprecise steering and uneven tire wear. Regular inspections and replacement of worn parts is important.
- Rack and pinion boots – Rubber boots on the ends of the steering rack keep out dirt and debris. If torn, contaminants can enter and damage the rack.
- Wheel alignment – Proper toe, camber, and caster alignment ensures straight line stability, proper handling, and even tire wear. Alignment should be checked if the car pulls to one side or the steering wheel is off-center.
- Steering column universal joints – Wear in the U-joints or slip joint in the steering column can cause clunking or binding when turning.
While some of these items can be inspected visually, a thorough evaluation of the steering system should be part of regular maintenance by a qualified mechanic.
Steering Angle Adjustment
The maximum steering angle, or lock-to-lock turns, is an important factor in a vehicle’s maneuverability. In most cars, the steering angle is limited by physical stops in the steering rack or linkage to prevent the tires from contacting the suspension or body.
In some cases, such as after an accident or suspension modification, the steering stops may need to be adjusted to restore proper wheel clearance and full steering lock. This is a job for an experienced technician, as improper adjustment can lead to tire damage or loss of steering travel.
The procedure typically involves loosening the lock nuts on the steering stop bolts on the rack or linkage, turning the steering wheel to full lock, and adjusting the bolts to just contact the stops at the desired wheel position. It’s important to check clearance at full compression and rebound of the suspension.
Some vehicles have electronically controlled steering locks that limit travel based on speed and other factors. Adjusting these systems requires specialized software to access the control module and change the steering angle limits.
Steering Angle Sensor Learning Value Reset
As mentioned earlier, the steering angle sensor is a key component in stability control systems. It tells the control module the position and rate of rotation of the steering wheel, which is used to predict the vehicle’s path and detect instability.
Over time, the steering angle sensor can drift out of calibration, causing inaccurate readings and stability control faults. Symptoms can include warning lights, pull to one side, or unintended stability control intervention.
In many cases, a steering angle sensor can be recalibrated without replacement by performing a learning value reset. This procedure allows the control module to relearn the center position and range of the sensor.
The exact steps vary by make and model, but the general process is:
- Park on a level surface with the wheels pointed straight ahead.
- Turn the ignition on but do not start the engine.
- Using a scan tool, access the steering angle sensor calibration function in the stability control or ABS module.
- Follow the prompts to clear existing values and start the relearn process.
- Slowly turn the steering wheel all the way to one lock, then all the way to the other lock.
- Return the wheel to center and wait for the scan tool to indicate completion.
- Cycle the ignition and test drive to verify proper operation.
On some vehicles, the learning procedure can be done without a scan tool by performing a specific sequence of key and steering wheel inputs. Consult the service information for the exact procedure for your vehicle.
It’s important to note that a steering angle sensor relearn should only be performed if the sensor and steering components are in good condition. If the sensor is faulty or there is binding or play in the steering system, those issues should be addressed first.
Steering Control Actuator Adjustment
Vehicles with active steering systems, such as variable ratio or rear wheel steering, use electric actuators to change the steering geometry on the fly. These actuators, located on the steering rack or rear suspension, are controlled by the power steering module.
Like any electromechanical component, steering actuators can wear out over time and may require adjustment or replacement to restore proper function. Symptoms of a faulty actuator can include steering bind, inconsistent assist, or faults in the power steering or stability control systems.
Adjusting a steering actuator typically requires a scan tool to access the power steering module and enter an adjustment mode. The technician then manually positions the actuator to the specified home or zero position and commands the module to relearn the range of motion.
It’s crucial to follow the manufacturer’s procedures exactly, as improper adjustment can lead to steering malfunction or damage to the actuator. In some cases, worn actuators may need to be replaced rather than adjusted.
Steering Lock Control Unit Registration
Most modern vehicles have an electronic steering lock that engages when the ignition is turned off to prevent theft. The steering lock is typically integrated into the ignition switch assembly and is controlled by a dedicated module, often called the steering lock control unit.
If the steering lock control unit is replaced, it will need to be registered or paired to the vehicle to function properly. This is a security measure to prevent unauthorized replacement of the lock.
The registration process requires a scan tool and access to the manufacturer’s security gateway. The technician will need to provide proof of ownership and enter a security code or password to initiate the pairing process.
Once accessed, the scan tool will prompt the technician to input the serial number or identification code from the new steering lock control unit. This code will be verified by the security gateway and, if valid, the new unit will be registered to the vehicle.
Failure to properly register a new steering lock control unit can result in a no-start condition or loss of theft deterrent functions. It’s important to follow the manufacturer’s procedures and use a scan tool with the necessary security access to complete the process.
Steering Sensor Initialization
In addition to the steering angle sensor, some vehicles have additional sensors that monitor steering input and assist force for use in lane keeping assist, parking aid, or autonomous driving systems. These sensors, which can include torque sensors, pressure sensors, and electric motor position sensors, may require initialization or calibration after replacement or certain steering system repairs.
The initialization process typically involves using a scan tool to access the steering control module and command a sensor relearn. This may be done with the vehicle stationary or may require driving in a straight line at a certain speed for a specified time to allow the sensors to calibrate.
As with any calibration procedure, it’s important to follow the manufacturer’s instructions exactly and ensure all prerequisites are met before starting. Failure to properly initialize steering sensors can result in faults or improper operation of driver assist systems.
Steering Sensor Revision
Occasionally, vehicle manufacturers may release updated software or calibrations for steering system sensors to improve performance or address issues. These revisions may be part of a technical service bulletin or recall campaign.
Performing a steering sensor revision typically involves using a scan tool or manufacturer-specific programming equipment to access the steering control module and upload the new software or calibration files. The process may require entering security codes and following specific procedures to ensure proper installation.
It’s important to use the correct software and tools for the specific make, model, and year of the vehicle, as using the wrong files can cause steering malfunction or other issues. Always follow the manufacturer’s instructions and verify the update was successful before returning the vehicle to service.
Steering Torque Actuator Adjustment
Some vehicles with electric power steering use a torque actuator, also known as a power pack, to provide steering assist. The torque actuator is typically mounted on the steering column and uses an electric motor and reduction gears to apply assist force to the steering shaft.
Like other steering actuators, the torque actuator may require adjustment or relearning after replacement or certain steering system repairs. This is to ensure proper centering and assist feel.
The adjustment process usually involves using a scan tool to access the power steering control module and command a torque sensor relearn. This may be done with the vehicle stationary and the wheels pointed straight ahead, or may require driving at a certain speed and steering input pattern.
Proper torque actuator adjustment is critical for safe and predictable steering feel. An improperly adjusted actuator can cause inconsistent assist, steering pull, or loss of assist. Always follow the manufacturer’s procedures and use the correct tools to ensure a successful adjustment.
Steering Torque Actuator Adjustment Value Clear
In some cases, the power steering control module may store learned values or adjustments for the torque actuator that are no longer valid after a repair or component replacement. These stored values can cause incorrect assist levels or steering pull.
To restore proper operation, it may be necessary to clear the stored adjustment values using a scan tool. This allows the control module to relearn the correct values based on the current state of the steering system.
The process for clearing torque actuator adjustment values varies by manufacturer, but typically involves accessing the power steering control module with a scan tool and commanding a clear or reset of the stored values. This may be done as part of a larger steering system relearn procedure.
It’s important to only clear the adjustment values if there is a specific reason to do so, such as after a component replacement or to address a known issue. Clearing the values unnecessarily can cause temporary steering issues until the system relearns the correct settings.
Conclusion
The steering system is a critical component of any vehicle, allowing the driver to control the direction of travel safely and predictably. From the steering wheel to the road, a complex system of mechanical, hydraulic, and electronic components work together to provide precise and responsive steering control.
As vehicles become more advanced, steering systems are increasingly integrated with driver assist and autonomous driving technologies. This adds complexity and requires specialized knowledge and tools to properly diagnose and service.
Whether performing a basic alignment or a complex steering actuator adjustment, it’s important for technicians to stay up to date on the latest procedures and best practices. By understanding how steering systems work and following manufacturer guidelines, technicians can ensure safe and reliable operation for their customers.