Hello Paul, it is true that faulty oxygen (O2) sensors can increase your car’s fuel consumption and emissions. To understand how oxygen sensors affect your car’s fuel economy, it is helpful to understand their function.
The oxygen sensor is located in the exhaust system and measures the amount of unburnt oxygen in the exhaust gases after combustion. It sends this information to the engine control unit (ECU), which uses it to determine whether the air-fuel mixture is too rich (too much fuel) or too lean (too much air). Here is how oxygen sensors impact fuel economy:
The ECU continuously regulates fuel delivery based on the information from the oxygen sensors. If the air-fuel mixture is too lean, the ECU will increase the amount of fuel delivered. Conversely, if the mixture is too rich, the ECU will decrease fuel delivery.
When an oxygen sensor is faulty, it provides incorrect readings, causing the ECU to deliver more fuel than necessary. This results in decreased fuel economy and poor engine performance. A malfunctioning oxygen sensor can also lead to symptoms such as rough idling, hesitation, or black exhaust smoke.
Faulty oxygen sensors can negatively affect emissions by delivering more fuel than can be burned, leading to incomplete combustion. This incomplete burning of fuel can increase emissions of harmful hydrocarbons (HC) and carbon monoxide (CO).
This may damage components of the emission system, such as the catalytic converter (CAT), which can become filled with excess fuel. This can result in CAT meltdown or blockage in the emission system. Often, a check engine light will illuminate because the emissions no longer flow freely, causing backpressure in the combustion system.
Your car is likely to fail an emissions test because its emission levels may exceed legal limits.
Common causes of oxygen sensor failure include normal wear and tear or ageing. Leaking oil from worn piston rings or coolant leaks from damaged cylinder head gaskets can contaminate and damage oxygen sensors. Additionally, the use of adulterated or smuggled leaded petrol can harm them.
Broken circuits, damaged wiring, or faulty connectors can also prevent oxygen sensors from functioning correctly.
While faulty oxygen sensors may not pose immediate safety issues such as problems with brakes or steering, they should not be ignored. They can lead to poor engine performance, increased running and maintenance costs, and potentially expensive damage to the catalytic converter.
In many modern vehicles, if the check engine light comes on, it is advisable to check the oxygen sensors and carry out a computer diagnostic test.