Code IBST_a157 was reported by the “Brake booster (iBooster)” controller in the car. The letter “a” in the middle places it among entries of the alert type.
The electromechanical brake booster. It provides pedal assistance and works together with regenerative braking. These codes show up as a harder pedal and a message about reduced braking — the brakes still work mechanically, but need much more force.
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.
Scl: ESPiB3_pMC1 Invalid Value
DTS off set is too high Confirmed
Phase Current 2 out of range low. ECU internal fault, check wiring to the unit and or re-flash. If problem continures after several power cycles, reolace unit.
The measured average coil resistivity is above the max threshold.
Linear Position Sensor Channel 1 Sensor internal failure
FW set in case of temperature degradation level1
Vpre was externally feed. Possible internal shortcircuit. ECU internal fault, check wiring to the unit and/or re-flash. If problem continures after several power cycles, reolace unit.
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.