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.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing


Experienced Mechanic?

Earn up to $70/hr

What others are asking

Horn not working in car
Horns are a simple circuit to check. Check for power and ground at the horn while an assistant holds the button. If you have both, the horn itself is bad. Newer cars are usually ground side switched. If there is...
Transmission needs new clutch assembly will I damage the transmission further driving on it until the dealer gets the new part
If the dealer needs to overhaul the transmission for a bad or broken clutch, you may do additional damage (https://www.yourmechanic.com/article/is-it-safe-to-drive-with-a-slipping-transmission) driving it before they get to the repair. My suggestion is to ask the service center that will be doing...
When doing a radiator flush - do you need to replace the thermostat or any other components of the cooling system
Doing a radiator flush does not require any other component to be replaced. However, if the system has a lot of debris and scale in it, the thermostat (https://www.yourmechanic.com/services/thermostat-replacement) may need to be replaced if it gets clogged or corroded....
Car won't start, can't be jump-started. 2008 BMW 535xi
Hey there, thanks for writing in about your 2008 BMW 535xi. A no crank, no start condition indicates a problem with the starting system. This could be the starter itself (https://www.yourmechanic.com/services/starter-replacement) or the starting circuit. In your vehicle, power to...
what do i need to do when my tire pressure, electric steering and vehicle stability lights come on
Due to the impact of another vehicle hitting your car, there may be several things wrong that may or may not be visible such as the wheel speed sensors (https://www.yourmechanic.com/services/wheel-speed-sensor-replacement). Your car is equipped with wheel speed sensors at each...
Key won't turn in ignition to start car. Silence...desperation....
Hello. If the key will not turn in the ignition, then either the key is bad or there is a problem with the key lock cylinder (https://www.yourmechanic.com/article/symptoms-of-a-bad-or-failing-ignition-lock-cylinder). Most of the time, this is caused by a failure in the key...
Harsh ride over potholes
Hi there: In general, OEM parts are designed to maximize comfort and tend to wear out sooner than they really should. This is why OEM tires wear out so quickly. Aftermarket parts (https://www.yourmechanic.com/article/is-an-aftermarket-car-part-as-good-as-an-oem-car-part-by-brady-klopfer) (in general) are designed to maximize performance...
Does not idle well.
You may have a dirty or failing idle air control valve. The idle air control valve reads the air intake as it is mixed with fuel prior to being injected into the engine at low speeds and at idle. Since...
Occasionally there is a grinding noise when braking to a stop then engine stall.
Hi there. If the noise is only heard when the brakes are applied, then the rotors and pads are rubbing metal to metal. This can make a grinding noise that is heard throughout the vehicle. For the vehicle stalling at...

Related articles

How to Tell If Your Car Switches Are Dying
Since Since every part of your car is controlled or operated by a switch in some fashion, it is to be expected that the switch will eventually fail. Some of the most commonly used switches in your car are: Power...
Symptoms of a Bad or Failing Ignition Switch
If your car cannot start, starts but quickly dies, or has electrical components that stopped working, you may have to replace the ignition switch.
How to Replace an Ignition Relay
Common signs of a damaged or broken ignition relay include a low/dead battery, the car stalling or not starting, or loss of power to the dash lights.