Q: How Does a Keyless Push-Button Ignition Work?

asked by on November 19, 2015

How does a keyless push-button ignition work?

Push-button ignition system designs are highly technical and vary between manufacturers. Here, in a nutshell, is how they work.

When you push the “engine start” button, that button sends an electrical command (voltage signal) to several control modules (computers). One control module (we’ll call it the body control module) uses antennas located inside your vehicle and sends out a radio signal to the key in your pocket. This reaction wakes up the RFID chip inside the key, and asks it to identify itself. The RFID chip in the key responds to the ID request with a radio message of its own where it sends its ID code back to the body control module.

The other control module that received the “engine start” command is the engine computer. We’ll call it the powertrain control module (PCM). The PCM is ready to start the engine, but it needs information from the BCM first, since the BCM controls the keyless entry system of the vehicle.

If the BCM accepts the RFID code from the key, it communicates this to the PCM, and the engine start is enabled. If an unprogrammed key is used, the BCM rejects the key code. The reject notice is communicated from the BCM to the PCM and the engine start is disabled. All of this communication occurs in less than 1/2 second!

This same process occurs to automatically unlock the doors of your vehicle whenever you grab a door handle.

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