Auto Vehicle Hold, often called Auto Hold, is a driver convenience system that maintains the vehicle in a stationary position without requiring continuous input on the brake pedal. This function engages automatically after the car has come to a full stop, providing temporary braking force. The system allows the driver to momentarily relax their leg while waiting at lights or in traffic, enhancing comfort.
How Vehicle Hold Works
The Vehicle Hold system relies on the car’s computer-controlled braking components. When the vehicle is stopped completely, speed sensors detect zero movement, signaling the system to engage the holding function. This engagement is confirmed by a light on the dashboard, assuring the driver that the feature is active.
The core mechanism involves temporarily preserving the hydraulic pressure within the brake lines that was generated when the driver initially pressed the brake pedal to stop. A solenoid valve within the Electronic Stability Program (ESP) or Anti-lock Braking System (ABS) module closes, effectively locking the pressure in the wheel cylinders. This sustained pressure keeps the brake pads clamped against the rotors, preventing the wheels from turning.
The system is designed to automatically disengage when the vehicle is ready to move again. When the driver lightly presses the accelerator pedal, the vehicle’s control unit recognizes the intent to drive. It commands the solenoid valve to open, releasing the hydraulic pressure and allowing the car to proceed smoothly without any noticeable delay or lurching.
Practical Applications for Drivers
The most frequent use for Auto Hold is in congested, stop-and-go traffic scenarios. Instead of holding the brake pedal down repeatedly while inching forward, the driver can rest their foot during frequent stops. This reduction in continuous physical effort significantly lowers driver fatigue in heavy urban environments.
Another beneficial application is preventing the vehicle from rolling backward when starting from a stop on an uphill incline or creeping forward on a decline. The system keeps the vehicle firmly in place, eliminating the need for the driver to quickly transition their foot from the brake to the accelerator. This makes hill starts smoother and reduces the chance of accidental movement.
The feature is also useful during extended waits, such as at long traffic lights or railroad crossings. By maintaining the braking force, the system allows the driver to remain attentive without the distraction of managing pedal pressure.
Vehicle Hold vs. Parking Brake
Understanding the distinction between Auto Vehicle Hold and the electronic parking brake (EPB) is important. Vehicle Hold is a temporary convenience feature relying on hydraulic pressure to keep the car stopped. The parking brake, conversely, is a permanent mechanism that uses mechanical or electrical actuators to physically lock the wheels, securing the vehicle indefinitely.
The EPB is designed for long-term immobility, such as when parking the vehicle or leaving the driver’s seat. It engages a dedicated set of brake shoes or clamps the rear brake calipers with electric motors, providing a robust mechanical lock independent of the service brakes’ hydraulic circuit. This ensures the vehicle remains stationary even if the engine is turned off.
Auto Vehicle Hold has limitations that prevent it from being used as a parking brake substitute. The system monitors parameters such as the driver’s door status and seatbelt usage. If the driver opens the door, unbuckles their seatbelt, or if the vehicle sits stationary for an extended period, the system will disengage the hydraulic hold.
In many modern vehicles, when the Auto Hold system detects one of these disengagement conditions, it automatically applies the electronic parking brake. This transition ensures that the vehicle remains securely stopped even as the temporary hydraulic pressure is released. This automated safety measure prevents accidental rolling when the driver exits the car.
Auto Hold is designed purely for brief stops while the driver is present and actively operating the vehicle. It releases easily upon accelerator input, making it unsuitable for parking. The EPB must always be engaged any time the driver intends to leave the vehicle or turn off the ignition.