The barometer stopped giving usable readings (ERR BARO)

What ArduPilot says:

• ERR BARO (Subsys 18)

Code 4 (unhealthy): the barometer in use gave no reading for 0.5 s, the very same value for 2 s, or a pressure or temperature that cannot be real. Code 0: it is healthy again. Holding height rests on the barometer, so a fault that lasts shows as height wandering in AltHold and Loiter. Code 2 (glitch) is in the list of codes but nothing in Copter or Plane 4.6 and 4.7 writes it.

What to do, most likely first

1. The sensor or its bus on the flight controller dropped out for a moment: a power dip, or a board that is failing.

   CheckBARO.Health in the log falls to 0 at the same moments, and BARO.Press holds one value.

   FixCheck the 5 V supply under load (POWR.Vcc in the log). If the error returns on a steady supply, the board needs replacing.

2. An external barometer's cable is intermittent.

   CheckOnly the external instance (BARO.I 1 or higher) shows the gaps.

   FixRe-seat or replace the cable, or set BARO_PRIMARY to the barometer on the board.

Parameters to look at

Where to do it:Setup & Tuning Guide