Resistance - 7 Ohm.
Cable colors:
1 cable - black;
2 cable - white;
3 cable - white;
4 cable - grey;
The sensor is part of the emissions control system and feeds data to the engine management computer. The goal of the sensor is to help the engine run as efficiently as possible and also to produce as few emissions as possible.
A gasoline engine burns gasoline in the presence of oxygen (see How Car Engines Work
for complete details). It turns out that there is a particular ratio of
air and gasoline that is "perfect," and that ratio is 14.7:1 (different
fuels have different perfect ratios -- the ratio depends on the amount
of hydrogen and carbon found in a given amount of fuel). If there is
less air than this perfect ratio, then there will be fuel left over
after combustion. This is called a rich mixture. Rich
mixtures are bad because the unburned fuel creates pollution. If there
is more air than this perfect ratio, then there is excess oxygen. This is called a lean
mixture. A lean mixture tends to produce more nitrogen-oxide
pollutants, and, in some cases, it can cause poor performance and even
engine damage.
The oxygen sensor is positioned in the exhaust
pipe and can detect rich and lean mixtures. The mechanism in most
sensors involves a chemical reaction that generates a voltage
(see the patents below for details). The engine's computer looks at the
voltage to determine if the mixture is rich or lean, and adjusts the
amount of fuel entering the engine accordingly.
The reason why the
engine needs the oxygen sensor is because the amount of oxygen that the
engine can pull in depends on all sorts of things, such as the
altitude, the temperature of the air, the temperature of the engine, the
barometric pressure, the load on the engine, etc.
When the oxygen
sensor fails, the computer can no longer sense the air/fuel ratio, so
it ends up guessing. Your car performs poorly and uses more fuel than it
needs to.