Also known as the Interior Oxygenator. KITT could release oxygen into his driver compartment and provide air to passengers if he was ever submerged in water or buried in earth. This is also used to overcome the effects of certain drugs.
The Oxygen Vent appears to be in a slide-down panel somewhere on the overhead console but it was never established exactly where. There was a button on KITT's right switch pod that said Oxygen, but it was never used. KITT always automatically lowered the Oxygen Vent himself.