a quote taken from honda-tech.com about baro sensor and it does ..
The purpose of a Baro sensor is to determine air pressure is when at different elevation(s). Its a way to more percisely control your Injectors.
Map sensors do provide good info for elevation, but to be more accurate, a Baro sensor can be also added for additional accuracy of incoming air density.
This additional accuracy, also makes for a more accurate pulse injection at the injectors, improving performance, and of course, emissions.
The goal is to keep an engine running as close to optimum, which is 14.7 to 1. (14.7 parts air to 1 part fuel).
Its an important sensor, particularly when you are moving from say, sea level on up to 10000 feet.
I like to think of it is alot like when your ears fill and pop at different altitudes.
Basically, the system never lets that happen, and makes sure all incoming air mass and pressure is watched more accurately to prevent any "hiccups" that result in lean or overly rich mixtures.
Climbing hills often results in hard acceleration (very rich), and coasting down hill, the opposite, but the pressure varies on the way up, and down.
Its just a way for the system to "more quickly" alter fuel mixtures to rising and dropping fuel requirements based on elevation changes.
Even slight ones.
It uses a pressure "membrane" in most of them, that is a type of electrical rheostat. (a rheostat is a variable resistance reader like your dash light dimmer that allows you to raise and lower the brightness of your dash).
At certain elevation points, the electrical resistance changes to these rising and lowering pressures, and makes adjustments based on those inputs at the ECM.
If your Baro sensor goes out of "range" that means that the sensor is giving a faulty or intermittent signal to the ECM.
The ECM has to "guess" what the sensor (would give) by using a predetermined set of programmed parameters, Air pressure, just using the Map sensor as a reference point.
Its not entirely accurate, but it works better than nothing at all.
in other word, yur sensor might already konked ..