Code IBST_a116 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.
The UBB voltage is in undervoltage level2 failure range. System shall be in 'ReducedPerformance' state.
Read failed failure for parameter MasterCylinderLength
The measured average coil resistivity is below the min threshold.
UB6 to UBB plausi voltage divider drift failure (large deviation in the UB6 to UBB ratio)
Version of RPS calibration data in NvM inconsistent with version in SW. ECU internal fault, check wiring to the unit and/or re-flash. If problem continures after several power cycles, reolace unit.
Phase Current 1 out of range high. ECU internal fault, check wiring to the unit and/or re-flash. If problem continures after several power cycles, reolace unit.
Failure word in case of actual EEPROM size detection failed or EEPROM size mismatch wrt to configured size and actual size mounted on layout. ECU internal fault, check wiring to the unit and/or re-flash. If problem continures after several power cycles, reolace unit.
There is a permanent deviation between the target speed and the actual motor speed
EPBR_systemStatus message not received or corrupt
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.