What Are the Reasons Why a Mercedes Key Cannot Unlock the Door?

[StChristopher]

The reasons why a Mercedes key cannot unlock the door are: 1. The Mercedes key battery is dead; 2. The remote key is being interfered with by signals; 3. The connecting mechanism between the door handle and the lock is faulty. Models under the Mercedes brand include: Mercedes GLS, Mercedes GLE, Mercedes GLC, Mercedes GLA, and Mercedes CLA. Taking the 2021 Mercedes GLS as an example, it is a mid-to-large-sized car with body dimensions of: length 5214mm, width 1956mm, height 1823mm. The 2021 Mercedes GLS is equipped with a 2.5T turbocharged engine, delivering a maximum horsepower of 313PS, a maximum power of 230kW, and a maximum torque of 400Nm, paired with a 9-speed automatic transmission.

[SanJuliet]

That day when I returned from a business trip, dragging my suitcase to the garage, I found that pressing the Mercedes key didn't work. First, I tried switching to the spare key, but it didn't help either, ruling out the possibility of a dead key battery. Later, peering through the car window, I noticed the dashboard lights were on with a warning, and then I realized the central locking system had failed due to a dead battery. In fact, Mercedes' door locking system is more complex than that of ordinary cars. The electronic components include the key signal receiver module, door handle sensor, and body control module—any one of these failing can cause the system to stop working. The mechanical keyhole is usually well-hidden, requiring you to pry open the decorative cover with the key head for emergency access. I recommend car owners first rule out battery issues, then check if the key battery contacts are oxidized, as these steps can resolve 80% of sudden malfunctions.

[JaceLee]

I've researched the principle behind Mercedes smart key failures: the key emits a 315MHz low-frequency signal, which is received by the vehicle's antenna and verified by the roof control module. Once during a customer repair, I used a diagnostic tool and found that the antenna amplifier under the passenger footwell was damp. Some owners also reported that stacking the key with a phone, especially one with a metal case, can block the signal. More troublesome are software glitches, like when a failed system update causes the anti-theft module to crash. The proper troubleshooting sequence should be: 1. Physically open with the key; 2. Replace the battery and reposition the key; 3. Disconnect the negative battery terminal for 5 minutes to reset; 4. Only as a last resort visit the dealership to reflash the software.

[LeRylee]

Don't panic when your key fob fails. Here's my reliable solution. First, check if the door handle feels abnormally warm - last winter there was a case where the heating wire short-circuited and burned out the sensor module. Then see if the key's indicator light flashes when pressed. If it doesn't, it's definitely a key issue - try replacing the CR2032 battery. If the light flashes but the car doesn't respond, it's likely signal interference. Nowadays, many underground garage LED lights emit 2.4GHz interference waves - try operating farther from the lights. As a last resort, use the mechanical key. Mercedes has a clever design: pull out the metal key head and insert it into the small square hole under the driver's door handle to unlock.