How To Reprogram A Key Fob After Replacing Its Battery

Keyless entry systems have been a standard feature on many vehicles for the past two decades. For the most part, not a lot has changed with the wireless remotes, known as fobs. They use a microchip that is powered by a small battery and the microchip emits a precise frequency to a control module. The control module can then activate the door locks, trunk, panic alarm, or even start the engine. Key fob batteries can last anywhere from 1–5 years, depending on the conditions of how they are stored and how often the keyless entry system is used. In most cases, a key fob battery can be replaced, and the fob will resume its normal operation, but occasionally, the fob will have to be reprogrammed. Stick with us as we’ll cover the symptoms of a dead fob battery, how to test it, how to change the key fob battery, and how to repogram a key fob after replacing the battery.

Why Does A New Battery Affect Key Fob Functionality?

Unlike other circuit boards that are found in computer modules, radios, display units, and amplifiers, the microchips in a key fob do not have capacitors. Capacitors store electrical energy, similar to a battery. When the battery is removed from the key fob, the fob can lose its ‘memory’ or programming. If the key fob is not working after replacing its battery, a reprogramming procedure may be required.

Symptoms Of A Bad Key Fob Battery

The typical symptoms of a dead or low-voltage battery are:

• The key fob does not operate the door locks at all.
• The key fob will intermittently operate the door locks.
• The trunk release does not operate.
• The remote start does not operate.
• The panic button does not work.

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How To Test A Key Fob Battery

If you suspect the battery in your key fob requires replacement, you can test it. Much like a car battery, this is done by removing the battery from the fob with the steps mentioned below and testing it with a multimeter. Key fob batteries, such as the CR2032 or CR1616, should measure around 3V. If the key fob battery measures below 2.7V, it will no longer operate correctly. Our guide on testing a car battery with a multimeter provides more information on how to use this device.

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How To Replace A Key Fob Battery

Changing the battery in a key fob is a simple task that requires very basic tools and, on some vehicles, can be done without any tools at all. The following are the steps to replace a key fob battery:

1. Locate the cutout slot on the fob. This is used to separate the key fob halves.
2. Using a flat-blade screwdriver, key, fingernail, or a spreading knife. Separate the fob halves by carefully prying the fob halves apart.
3. Pay close attention to which way the battery is facing, as well as what type of battery is installed. Some key fobs have markings indicating the battery’s correct orientation, others do not.
4. Remove the key fob battery by prying it upwards.
5. Replace the key fob battery with the correct replacement battery. (The battery type will be indicated on the battery itself)
6. Double-check the battery direction/orientation.
7. Position the fob halves together and squeeze them together. An audible ‘click’ should be heard.
8. Press the key fob buttons; the key fob should illuminate a red light (if applicable).
9. The key fob should now be functioning. If the fob is not operating as it should, reprogramming may be necessary.

How To Reprogram A Key Fob

There are many different vehicles with keyless entry systems. We will not cover all of them, but we will cover one of the most common fobs that requires resetting after battery changing, that being a Honda key fob. Honda keyless entry systems can be prone to needing reprogramming more than other systems. The following are the steps required to reprogram a key fob on a Honda vehicle such as a Civic or Accord:

1. Insert the key into the ignition cylinder and position the cylinder in the ‘ON’ position.
2. Press and hold the ‘Lock’ button on the key fob for approximately 1–2 seconds.
3. Turn the key to the ‘OFF’ position and wait 1–2 seconds.
4. Turn the key back to the ‘ON’ position, wait 1–2 seconds.
5. Press and hold the ‘Lock’ button again for another 1–2 seconds.
6. Turn the ignition key to the ‘OFF’ position.
7. This process will need to be repeated four times. On the fourth cycle, the doors will lock. This confirms the key fob has been correctly programmed.
8. Confirm operation by pressing the ‘Lock’ and ‘Unlock’ buttons while monitoring the door lock operation. If the locks do not lock and unlock correctly, the fob has not been programmed.

Newer Honda vehicles (2003 to present) will likely have the key fob integrated onto the vehicle key. If you are programming multiple key fobs to operate the door locks, you can insert the additional keys into the ignition cylinder after the fourth cycle to program them. By so doing, you won’t have to complete the entire programming cycle for each key.

Battery Types

Below is a list of key fob battery types from several major automakers.

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