CAT  uses sensors, that are called "absolute pressure sensors", which means they measure BOTH whatever pressure enters the sensor AND the air/atmospheric pressure that is constantly pushing down on you and me. (At Sea-Level = 14.7 psi, but CAT just reads 15 psi, for our example)

Why this type of sensor? Because they don't need a "vent" on the backside. If you had a vent, then dirt, moisture,  and debris could easily ruin or corrode the sensor.

So, If you have sensors on an engine, that read this type of signal, THEN you need an Atmospheric sensor reading, SO the ECM(computer) can do some simple math and calculate the correct oil, fuel, boost pressure readings.
Example: Oil pressure reading (from absolute sensor) = 100 psi, but engine is at Sea-level, so Atmospheric reading 15 psi. The ECM takes 100 psi minus 15 psi = 85 psi of Actual oil pressure.

Now, in your case, by you unplugging the atmospheric sensor, then that caused the ECM to default the oil pressure, boost presure and fuel pressure signals, Because it couldn't do the necessary calculations, WITHOUT a good atmospheric signal (You created an "open circuit", by unplugging that Atmospheric sensor)