Code EPAS3P_a078 was reported by the “Power steering — 3rd gen, primary” controller in the car. The letter “a” in the middle places it among entries of the alert type.
The primary channel of third-generation power steering. Newer cars have a redundant steering system — this is its main half.
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.
Phase disconnect FET startup check error
Torque sensor 1 supply voltage error
Torque sensor 1 observed failure with the voltage supply
Steering assist reduced and EAC inhibited
Due to sustained torque, output torque is limited
The electric power assist steering (EPAS) Electronic Control Unit (ECU) is not receiving the drive inverter torque message, which may be the result of controller area network (CAN) bus issues.
The electric power assist steering (EPAS) Electronic Control Unit (ECU) does not receive the drive inverter torque message.
The drive inverter torque message is received by the electric power assist steering (EPAS) Electronic Control Unit (ECU).
External Angle Controller is inhibited.
Hysteresis controller correlation error
|torque command path1 - path2| > 0.6Nm
Power-up arbitation between primary and secondary ECU failed
Master and Slave ECUs INIT Arbitration Failed
VCFRONT_LVPowerState message not received
VCFRONT_LVPowerState message is not received by EPAS
EPAS receives VCFRONT_LVPowerState message again
Torque sensor 2 signal invalid
Invalid Torque sensor 2 signal received by EPAS
Gate drive SPI communication error
Gate drive SPI communication errors
Invalid EPAS3P/S_statusCounter value received
EPAS3P/S_statusCounter is not incrementing correctly
EPAS observes EPAS3P/S_statusCounter incrementing correctly
Estimated motor parameters exceed expected values
if Ke 25.6mV/(rad/s), Ke=25.1mV/(rad/s)
Floating point calculation error
Microcontroller floating point unit errors
Reduced assist, EAC inhibited, and SASQF = UNDEFINABLE_ACCURACY
Fault signaling protocol gate driver power cut
Gate Drive PWR status signal is monitored wrto the FSP /SMU signal set to LOW). If they do not agree fault is set
Motor position sensor 1 logic error
Motor position sensor 2 signal undervoltage
Internal watchdog error occurred
CAN transmit error counter is above 255
Assist reduced due to supply undervoltage
Motor control feed-forward correlation error
| estimated torque (back calculated from PWM duty & observer) - Command torque | > 1.2Nm
EPAS3P/S_status message not received
EPAS3P/S_status message is not received by EPAS
EPAS3P/S_status message is received
Gate drive bridge undervoltage
Vbridge returns to expected value
Invalid DAS_steeringControlChecksum value received
Unexpected DAS_steeringControlChecksum value received by EPAS
EPAS observes expected DAS_steeringControlChecksum value
Proportional-integrator motor control error
(Vq intgl square + Vd intgl squre) > 20 or (Phase A 160)
(Vq intgl square + Vd intgl square) < 20
Invalid SCCM_steeringAngleSensorCounter value received
SCCM_steeringAngleSensorCounter is not incrementing correctly
EPAS observes SCCM_steeringAngleSensorCounter incrementing correctly
Reduced steering assist and SASQF = UNDEFINABLE_ACCURACY
Torque sensor 1 observed failure with the linearity calibrations
Vehicle speed estimation correlation error
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.