Why does the Mercedes key show a red light and fail to lock the car?

[DeIker]

Mercedes key showing a red light and failing to lock the car may be due to insufficient battery power or being too far away. Check if the remote key's battery is low: This can be tested by measuring the battery voltage with a multimeter. When the battery is low, the voltage drops, causing unstable performance of the internal circuits, which results in reduced wireless communication range. If the battery isn't too low to power the circuit, you can try locking the car by getting closer to the vehicle. Ensure proximity between the remote key and the car body: Remote keys commonly use either short-range infrared sensing or short-range radio frequency. Regardless of the type, both the transmitting and receiving circuits are prone to malfunctions, which can be attributed to electronic circuit design and components.