Code APS_w161 was reported by the “Autopilot — secondary processor” controller in the car. The letter “w” in the middle places it among entries of the warning type.
The second, supervising processor inside the Autopilot computer. It checks the primary processor's work and guards safety functions, chiefly automatic emergency braking. Codes from here often accompany APP codes and clear once camera calibration finishes.
The car is flagging that something is not right. Driving is usually still possible, but some function may be limited.
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.
Warns if APS detects that GPS antenna is unplugged
APS detects that GPS antenna is unplugged
GPS antenna is plugged in correctly
Warns if APS detects that Backup Autopilot is unhealthy
APS detects Backup Autopilot is unhealthy based on watchdog state or GPIOs
Backup Autopilot becomes healthy again
BMS has detected that one or more module temperatures exceeds the warning threshold
The BMS uses this for specfic exceptions triggered in code, like data exceptions or machine check errors
Indicates a BMB reference voltage has continuously been out of bounds
Any BMB reference voltage has continuously deviated outside the in-bounds threshold of the nominal voltage
All BMB reference voltages continuously remain within the in-bounds threshold of the nominal voltage
Other BMB voltage signals will be substituted given the reference voltage is unreliable
BMS sees the VCFRONT MIA while not in drive state
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.