Any change in altitude while you are traveling in your vehicle is sensed by the Jeep oxygen sensor. The data supplied to the onboard computer is just one of the many variables used to determine the correct air to fuel ratio for the Jeep engine to perform at its maximum level. When the oxygen sensor or any of the other sensors on your Jeep engine fails to operate, a sign from the onboard computer is sent to the dash illuminating the check engine light. This is how the operator of the vehicle will be informed there is a problem. In most instances, the loss of this data in the air fuel ratio will not be noticeable to the driver unless they are climbing a mountain at that particular time. When the Jeep oxygen sensor fails, a specific code is then stored in the computer until it is retrieved by the owner or a technician. This code along with all the others is listed in the Jeep service manual for your specific model. This is how the owner will know that the oxygen sensor is malfunctioning. The specific location of the oxygen sensor is in the exhaust system just after the exhaust manifold but before the catalytic converter. It can generally be seen by looking in this area from under the hood of the vehicle. It is the only probe or sensor on the exhaust pipe with a wire protruding from it. Very clean vehicles will have one located after the catalytic converter that tests the emissions, making sure the converter is working properly. The replacement of the oxygen sensor only requires the old one to be removed with a wrench and the new one put in its place. Disconnecting the battery is recommended since this is an electrical component. This will also clear all of the codes the computer has stored.