Car Starts, but Remote Locking & Unlocking Not Working? Here’s How to Fix It

Understanding how a keyless car works with the key is an important step in troubleshooting a rather unique scenario: the central locking button on the key is not working, yet the key is still able to start the car.

Firstly, because the car starts wirelessly (Comfort Access/Keyless Go), we know that the "Remote" section of the board (the top part with the radio circuitry) is successfully sending the authorization code to the car.

It is likely that your FEM needs testing. You can find out more on The ECU Pro's mail-in testing service below, or continue reading the blog for more info and troubleshooting.

What this tells you for diagnostics:

As a process of elimination to find the problem, if your keyless Start works but the buttons (Lock/Unlock) do not, you know that:

1. It is NOT the Radio Chip: We know the 315 MHz transmitter is healthy because it successfully talks to the car to allow the start.

2. It is NOT the Battery: The battery is strong enough to power the radio transmission.

3. It IS likely the Buttons: The fault is almost certainly the physical microswitches (buttons) themselves or the traces connecting those buttons to the main chip. Since the chip can transmit (proven by the starting), it just isn't receiving the "click" command from the user.

So, in the specific case where the car starts but remote locking/unlock isn’t working, BOTH the large coil and the top radio section are still functioning correctly.

You likely have a physical button failure or a broken trace on the board, specifically for the button inputs, rather than a blown radio chip.

So, Why Does the Central Locking Not Work?

1. The Physical Buttons are Broken (Most Likely)

Since the radio chip is capable of sending a signal (proven by the car starting), it simply isn't receiving the command to do so when you press the button.

• The Failure: The microswitches (the small buttons soldered to the board) are likely worn out, collapsed, or have broken solder joints.

• The Logic: The "Start" signal is triggered automatically by the car (via the 125 kHz coil), bypassing the buttons entirely. The "Lock" signal requires the physical button to close a circuit. If the button is broken, the chip never knows you are trying to lock the car.

• Test: Press the buttons firmly while listening closely. Do they still have a distinct, crisp "click"? Mushy or silent buttons often indicate failure.

It’s best to use our professional key repair service to inspect and fix your BMW key, and further check the coding of the key and FEM. It is possible for a key to be "coded" to the engine (allowing it to start) but not successfully "synced" to the central locking system. This is common with replacement keys or if the key has lost its rolling code synchronization.

Recommended Next Steps

The ECU Pro offers an affordable mail-in Front Electronic Module (FEM) repair service. To have your FEM repaired and key inspected, simply remove the FEM and mail it along with your key to us. Our professional team will either test, repair, or clone your unit.