<strong>O2</strong><br />This little beauty is the backfield safety of the fuel-injection world. It keeps the rest of the electrical soup in check. Too much fuel because of the MAP sensor? The O2 sensor picks it up and tells the computer to cut back. Too much air due to the IAC freaking out? Again, the O2 sensor tattles to the computer and brings everything back to what it should be. "What it should be" is often referred to as "stoichiometric" by the scientist types, which, of course, is a mixture where there is just enough air to completely burn the available fuel. In our case, it indicates a 14.7:1 air to fuel mixture that an engine "should" operate at. If anything else goes haywire in the system, the O2 sensor should catch it and let the computer know to adjust accordingly. Often, if something is out of whack and adjusted due to the oxygen sensor's input, the computer will light the check-engine light. If the O2 sensor dies, often the Jeep will run rich, which can be smelled at the tailpipe, but running rich will also kill the catalytic converter. This sensor should be replaced every third or fourth oil change. Take care of the O2 sensor(s), and it (they) will take care of you.