Code DI_a178 was reported by the “Drive inverter” controller in the car. The letter “a” in the middle places it among entries of the alert type.
The Drive Inverter — the power electronics that drive the motor. Codes from here show up as reduced power, a message about limited acceleration or, in worse cases, an inability to drive. Temperature codes are common too: the inverter protects itself under sustained load.
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.
Drive Inverter User Alert: Steering Angle offset exceeds plausibility
Steering angle offset exceeds sensor plausibility monitor threshold, faults sensor plausibility monitor
Steering angle offset has faulted stability and traction control. Vehicle should be driven with extreme caution.
Drive Inverter User Alert: Brake pedal required before shift can compelete
Drive Inverter Warning: power conversion at motor irrational
Drive Inverter Warning: Rear motor speed error
Drive Inverter Warning: CMP CAN node is missing.
Drive Inverter Warning: Regen limited significantly or disabled
The powertrain is limiting or disabling regen braking. This can be for multiple reasons: the battery pack is too hot or cold, the battery pack is fully charged or the battery pack is limiting for another regen.
The accelerator pedal might behave differently: it will provide less regen braking than normal when the accelerator pedal is fully depressed
Drive Inverter Warning: ADC low-reference bad
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.