How to Control a Car Light, Horn, or Central Locking System With an RF Remote Controller

It was not too long ago that you had to use your key to unlock your car doors and trunk, and to start your vehicle. If you wanted an alarm system, you would have to purchase that from an aftermarket company. In today’s automotive market, it is now commonplace for all cars to come with some sort of remote keyless entry that allows the owner to control the door locks, the alarm, the trunk, and even other components such as lighting and vehicle starting. These conveniences are great, but can be costly to repair should something malfunction. Understanding how this system works can assist you in diagnosing problems, and it can keep you from getting taken advantage of should a problem arise.

Part 1 of 2: How an RF remote works and what components are involved

Remote control systems are much the same in most vehicles. When you press a button on the remote, it sends out a signal to the car. That signal is picked up by a computer which then deciphers the information that is sent depending on which button you pressed. The computer then controls the system that involves the desired operation, whether it be the locks, the alarm or any of the other controlled circuits.

The most common components in this system are:

showing a series of different remotes

Remote control: Remote controls come in all shapes and sizes. They may come attached to the key or as a separate piece. In some cases they will be the key for push button ignition vehicles. When you press the button on the remote it sends a signal to the vehicle.

This signal can be interrupted due to distance or obstacles that may be in the path of the signal.

remote receiver

Remote receiver: The remote receiver is a control computer that usually has a small antenna on it. It is used to pick up the signal from the remote and send the signal to the proper place from there. This computer is usually programmed to work solely on the vehicle that it is installed on.

Most of the time it is mounted in the driver door, under the dash or under the rear dash panel near the rear window.

showing a master window switch on a door panel

Door control module: The door control module or the master window switch is what typically controls the functions of the windows and the door locks. It receives any signals from the remote related to door locks or window functions.

body control module mounted under a dash

Body control module: The body control module is what controls the majority of the interior electronics of the vehicle, as well as the alarm. It is typically located under the dash of most cars and can even be part of the fuse box.

In most vehicles, the body control module has the ability to control the lights, the horn, the alarm, the door locks, the windows, the climate control system and most of the other circuits.

powertrain control module mounted to a vehicle

Powertrain control module: The powertrain control module is the main control module that controls the functions of the engine and the transmission. This computer receives signals to start the car remotely, and turns on the various components required to start the engine.

The powertrain control module is usually mounted under the hood either near the engine or on the firewall. In some vehicles it is mounted in the trunk or under the dash.

Part 2 of 2: Problems that can occur

Though every car is different, there are some common issues that can occur with any RF remote controller. If you notice that something is not working correctly, you may be able to narrow down the problem if you know some of the common causes.

person using remote at a distance

1. The remote does not work. The most common cause of a remote that does not work is a bad battery in the remote. Typically, remotes have a small internal battery that will eventually drain. If you notice that the remote does not work all of a sudden, then the battery should be the first thing you check and replace.

A remote can also become unpaired with the vehicle. If this occurs, some manufacturers have reset procedures in place, while others require that you go to the dealer.

2. The remote only works close to the vehicle. This is also usually caused by a battery issue. If the battery is low, then the signal will not be as strong from the remote. Should this occur the battery should be replaced.

If a new battery does not help, then the issue may be with the remote itself, or more commonly with the receiver module.

3. Only certain buttons on the remote work. Most of the time this is caused by a failure inside the remote. When this occurs, many remotes can be taken apart and cleaned as the most common cause of a failure is internal debris affecting the contacts.

4. All functions work except for remote starting. Usually when this occurs it is because there is an issue with the vehicle’s powertrain control module. If the check engine light is on then the computer will disable the remote starting feature.

Though there are an unlimited number of possible problems that can occur and cause issues with this system, these are the most common. It is always a good idea to have a second remote available should the main one fail. If you cannot find an easy resolution to these problems, then further diagnostics will be needed, which usually require a scan tool and a voltage meter. If you do not feel comfortable handling this yourself, then you should enlist the help of a certified mechanic, such as one from YourMechanic, that can complete a vehicle inspection and find the source of your RF remote issues.


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