Code CHG_f125 was reported by the “Onboard charger” controller in the car. The letter “f” in the middle places it among entries of the fault type.
The charger inside the car that converts AC from the socket into DC for the battery. These codes cover AC charging problems — grid fluctuations, high line impedance, overheating.
The more serious level. The affected component has shut down or is running in limp mode. These codes belong in a service centre.
This is how the fault is named inside the car's firmware. For codes without a description it is the most precise clue there is — the name itself says what the event is about.
The text below comes from Tesla's technical documentation. We leave it in the original English so that translation cannot shift its meaning.
This fault indicates that the voltage decay after the supercharger external isolation test has happened too quickly.
During supercharger startup, the supercharger will open the output contactors after performing the external isolation test at 300V. The vehicle then monitors the time it takes for the 300V to decay. If the decay time is sufficient, the start-up sequence proceeds. The purpose of this test is to check the common mode isolation (DC+ to DC-) of the high voltage chain from the supercharger cabinet to the vehicle's fast charge contactors.
Copy it exactly, letter and number included. Photographing the screen is safest — codes often differ by a single digit, and mixing them up leads somewhere else entirely.
Some codes clear after a screen restart or after the car sits locked for a few hours. If the code does not come back, it was usually a one-off glitch.
A one-off entry and a code that appears after every drive are two different things. It helps a service centre enormously if you know exactly when it shows up.
With airbags, brakes, steering and high voltage there is no point waiting it out. With the other groups you can watch and see whether the code returns at all.
Error codes are only part of the picture. For cars on TesList you also see battery health pulled straight from the vehicle, plus a price calculator that works out from current listings what a given car is actually worth today.