At least 40 of the Diagnostic Trouble Codes which can cause your Check Engine Light (CEL), officially called a Malfunction Indicator Lamp (MIL) to come on are associated with the Oxygen Sensors. Some of the most common are:
The Engine Control Module (ECM), a computer that monitors engine functions and adjusts things like fuel mixture in the Electronic Fuel Injection (EFI) unit, uses input from the O2 sensors to determine things like fuel burning efficient and the functioning of the catalytic converter. The proper air/fuel ratio (aka lambda) is 14.7:1. Lambda is the Greek character used to designate that perfect stoichiometric ratio.
4 cylinder engines, straight 6's and some V-6 engines have only one catalytic converter.
There may be benefits to replacing the O2 sensor periodically for preventative maintenance. Replacing an aging O2 sensor that has become sluggish can restore peak fuel efficiency, minimize exhaust emissions and prolong the life of the converter.
Unheated 1 or 2 wire wire O2 sensors on 1976 through early 1990s vehicles can be replaced every 30,000 to 50,000 miles. Heated 3 and 4-wire O2 sensors on mid-1980s through mid-1990s applications can be changed every 60,000 miles. On OBD II equipped vehicles (1996 & up), a replacement interval of 100,000 miles can be recommended.
Sometimes they are hard to reach with a wrench and you need a special tool, which has a gap to fit around the wires.
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