Keyless Entry and Remote Start

Keyless entry lets you unlock and lock your vehicle without physically inserting a key. The key fob in your pocket or hand is a small radio transmitter. When you press the button, it sends a coded radio frequency signal — typically at 315 MHz in North America or 433 MHz in Europe — to a receiver module in the vehicle. The vehicle verifies the code matches its stored authorization and commands the door lock actuators through the BCM.

Early remote keyless entry systems used a fixed code. Press the button, it always sent the same signal. A thief with a radio scanner could record it and replay it later. Modern systems use rolling codes. Every time you press the fob button, the fob and the vehicle both advance to the next code in a synchronized mathematical sequence. The code that unlocked your vehicle five minutes ago will never work again. If someone records the signal and tries to replay it, the vehicle rejects it because it has already moved past that code in the sequence.

Many modern vehicles do not require you to press a button at all. The fob continuously broadcasts a low-power signal. Antennas around the vehicle detect when the fob is within a few feet. Pull the door handle and the vehicle authenticates the fob automatically and unlocks. This is passive entry. The same principle applies to push-button start — the vehicle detects the fob inside the cabin and allows the start button to function. If the fob is not detected inside the vehicle, pressing the start button does nothing.

Push-button start replaces the traditional ignition switch and key cylinder. Low-frequency antennas inside the cabin send a wake-up signal to the fob. The fob responds with its authentication code. If the code is valid, the vehicle enables the start button. Press the brake pedal and press the button — the engine starts. No mechanical key turn. The entire exchange between fob and vehicle happens in milliseconds.

When the fob battery gets weak, the range drops first. You have to be closer to the vehicle for it to respond. Then passive entry stops working — you may need to press the button on the fob directly. Eventually the fob signal is too weak for the vehicle to detect at all. Every push-button start vehicle has a backup method. Usually you hold the dead fob directly against the start button or a specific location on the steering column. A small coil in the button or column can power the fob chip through induction at very close range — close enough to read the transponder even without battery power. The owner manual shows the backup location for each vehicle.

Most fobs use a CR2032 or CR2025 coin cell battery. Replacement is straightforward — a small slot or screw on the fob case allows it to split open. After replacing the battery, the fob should work immediately without reprogramming because the code synchronization is stored in non-volatile memory. If a fob stops working after battery replacement, it may need to be re-synced using a manufacturer procedure — usually a specific sequence of ignition cycles and button presses.