What Is a Lambda Sensor?

Written by heather downey
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What Is a Lambda Sensor?
Car exhaust (Image by Flickr.com, courtesy of Chris Keating)

Most people don't take into account how much maintenance is required to keep a car running properly. They take care of things like oil changes and tire replacement, but engine, fuel system and exhaust repairs are often neglected until there's an obvious problem.

Lambda Sensor

The lambda sensor is also known as the exhaust gas oxygen sensor and is the key sensor in the engine fuel control feedback loop. A computer uses the lambda sensor to balance the fuel-oxygen mixture. The correct reading for fuel mixtures is rich as opposed to lean.

Output Range

Lambda sensor outputs range from 0.2 volts, which is lean, to 0.8 volts, which is rich. For a perfect balance, which is known as stoichiometric, there must be mixture of 14.7 parts air to 1 part fuel.

Read Frequency

The lambda sensor never remains constant, it is always changing. This is known as cross count. The injection system should switch between rich to lean about once per second; if it is lower than this, your sensor needs to be replaced.


A lambda sensor usually lasts between 30,000 and 50,000 miles, but it can stop working sooner if the sensor gets contaminated by lead from an antifreeze leak or if it becomes clogged with carbon. When the lambda sensor starts to fail, the check engine light may come on.


Before replacing your lambda sensor, do a diagnostic check to see what is wrong with your sensor. It could be a simple thing like a wiring problem that doesn't entail replacing the entire sensor.

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