Symptoms of a Faulty Lambda Sensor

by Ann LaPan
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A Lambda sensor measures the amount of unburned oxygen in a vehicle's fuel exhaust. If the oxygen level is too high or too low, the Lambda sensor sends a signal back to the vehicle's computer that tells it to adjust the air/fuel mixture so that the vehicle can perform optimally and within emission control standards. A Lambda sensor may become damaged, sluggish or completely fail. If any of these symptoms occur, a vehicle owner should address them soon, as waiting may cause further complications.

Poor Mileage

If a driver were to notice that he is not getting usual miles per gallon numbers, it may be the fault of the Lambda sensor because the vehicle's computer is not receiving notifications to change the air/fuel ratio, and the mixture might be too rich, consuming unnecessary fuel amounts. According to, the repair of a faulty sensor may increase mileage by as much as 40 percent.

Unusual Lurching Or Hesitation

An early warning signal of Lambda sensor failure in the form of an uneven idle can be noticed by a driver who feels the vehicle wanting to surge ahead when at a red light or stop sign. Or, conversely, when it is time to go, the driver feels the vehicle hesitating after the accelerator is applied.

Catalytic Converter Failure

According to, when the air/fuel mixture is too rich and is not corrected, thermal failure may be generated by red hot heat. In this case, the ceramic monolith can melt, and the vehicle's exhaust path could become blocked. Depending on the extent of the damage, engine power may become significantly reduced.

Dashboard Indicator Light

The "Check Engine" light may come on. A vehicle owner will have to have a reputable technician check the code.


A cold engine with a faulty Lambda sensor that has unburned oxygen in the catalytic converter may emit a "rotten egg" smell.

Decreasing Engine Power at Cruising Speed

A malfunctioning Lambda sensor may send an erroneous signal that the air/fuel mixture is too rich. The vehicle's computer will make the correction according to the signal that the Lambda sensor sent, decreasing the amount of fuel in the ratio, causing the spark plugs to misfire.

Emissions Test Failure

A malfunctioning Lambda Sensor may cause a vehicle's exhaust to be too rich in unacceptable emissions (unused hydrocarbons and carbon monoxide).

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