The air around us is about 80 percent nitrogen by volume, but your engine needs oxygen. While your engine could hypothetically get by with less fuel than it uses, the computer injects a little extra so that there’s always a fuel molecule next to an oxygen molecule in the combustion chamber. Your computer needs to maintain this critical ratio of fuel to air, generally, about 14 parts air to 1-part fuel, and it uses a number of sensors to monitor the amount of air going in, and the mixture of air and fuel coming out. All systems are different, but most follow this basic layout.
The mass airflow (MAF) sensor uses a heated wire hanging down in the airstream to monitor airflow by recording electrical resistance through the wire as it changes the temperature in the cooling airstream. The manifold absolute pressure (MAP) sensor compares pressure inside the intake manifold to pressure outside the engine, and the intake air temperature (IAT) does just what it sounds like. Your computer uses data from these sensors to figure out exactly how much air is going into the engine, so it knows what to expect in the combustion chambers.
Lift the SUV off the jack stands and lower it
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The first oxygen sensor
This sensor monitors what comes out, after the combustion event. To give you an idea of the O2 sensor’s importance, it’s worth noting that O2 sensors were around long before the electronic fuel injection system itself, and were the first and primary sensors installed on those primitive EFI setups. The second O2 sensor monitors oxygen content after exhaust gases pass through the catalytic converter, which works like a furnace to burn off excess fuel. If your first O2 sensor fails, the computer will use its best guess on what’s going on inside (“open-loop mode”) and will lose power and fuel economy as the sensor fails. Second O2 sensor failure will trigger a check engine light, and more drastic de-tuning; a condition called “limp-home mode,” designed to protect the engine while still allowing you to “limp home.”
Replacing the second O2 sensor
It isn’t any more difficult than replacing the first. For example, the first O2 sensor shown on our Jeep Liberty is only even visible through a tiny, four-inch window between the passenger-side fender well and the passenger-side exhaust manifold. It’s like the Isla del Muerte – only those who already know where it knows where to look for it. This is pretty typical of modern cars, which often have the first O2 sensor located very close to the engine and hidden somewhere in the engine bay. The Jeep’s second O2 sensor is also typical, in that it’s the first thing you see when you look under the passenger side of the car.
How to Replace the Front O2 Sensor on a 2005 Jeep Liberty V-6
Things You’ll Need: Ratchet, Oxygen sensor socket, Torque wrench
Oxygen Sensor Removal
Raise the vehicle’s front using a floor jack.
Lower the vehicle onto the jack stands. Position yourself under the vehicle to have a clear view of the exhaust pipe leading up to the side of the engine with the failed oxygen sensor. The “Bank 1” sensor is on the driver’s side of the engine and “Bank 2” is on the passenger’s side.
Trace the exhaust manifold — the exhaust pipe connected to the side of the engine — until you locate the failed upstream oxygen sensor, directly above the catalytic converter.
Check the oxygen sensor wiring. Trace it until you reach where it connects to the Liberty’s wiring, Lift upward on the locking tab on the wiring harness and disenable the sensor harness.
Take off the oxygen sensor and sensor socket with a ratchet. If the sensor does not loosen easily, heat the base of the sensor with a propane torch, then loosen it. Allow the sensor to cool, then remove it from the exhaust the rest of the way.
Oxygen Sensor Installation
Thread the new sensor into its hole in the exhaust, then using a torque wrench, tighten it to 22 foot-pounds and as well as oxygen sensor socket.
Plug the wiring harness of the sensor into the Liberty’s wiring harness and listen for its locking tab to click into place.