Code PCS_a100 was reported by the “Power conversion system (PCS)” controller in the car. The letter “a” in the middle places it among entries of the alert type.
The Power Conversion System — the combined onboard charger and DC/DC converter. It handles charging from the socket and generating the 12 V supply. These codes mostly show up as slower or interrupted charging.
The most common type. The car logged the event and may have shown it on the screen. The range is wide — from something trivial that clears itself to something that needs attention.
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.
An alert to indicate that this PCS may experienced viper chip issue that could impact AC charging functionality
PCS does not receive CAN messages from BMS
Charger does not receive all expected CAN messages from battery management system
Charger recieves all expected CAN messages from battery management system
Inability to AC charge, inability to precharge HV bus, inability to drive
Power conversion system DCDC malfunction detected, PCS service is required
When 5V logic power rail exceeds 5.8V continuously for more than 1 minute
Service alert will latch untill power cycled so will not be cleard at run time
Car unable to start or drive, LV battery and system cannot be supported, AC charging functionality may also be affected
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.