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Oxygen Sensor Failure Symptoms, Causes, and Repair Cost
A failing oxygen sensor can affect fuel mixture, emissions, fuel economy, and catalyst efficiency codes.
Oxygen sensors measure oxygen in the exhaust so the engine computer can adjust fuel mixture and monitor catalytic converter efficiency.
When an oxygen sensor becomes slow or inaccurate, it can trigger codes, reduce fuel economy, and make diagnosis of other problems harder.
Symptoms
- Check engine light
- Poor fuel economy
- Rough idle
- Failed emissions test
- Hesitation
- Codes such as P0171 or P0420
Common Causes
- Sensor age and contamination
- Exhaust leak
- Oil or coolant entering exhaust
- Rich fuel mixture
- Damaged wiring
- Connector corrosion
Severity
Moderate. The car may drive, but fuel economy, emissions, and catalytic converter health can suffer.
Typical Repair Costs
$150 to $500 per sensor
- Many vehicles have multiple oxygen sensors.
- Access can raise labor cost, especially on tight engine bays.
- Related exhaust leaks or wiring repairs can add cost.
Frequently Asked Questions
Can a bad oxygen sensor cause poor gas mileage?
Yes. Incorrect oxygen readings can cause the engine to use too much fuel.
Can an oxygen sensor cause P0420?
Yes. A slow or inaccurate sensor can make the converter appear inefficient.
Should I replace all oxygen sensors at once?
Not always. Diagnosis should identify which sensor is failing and whether another issue caused the code.
Related Articles
P0171 Code: System Too Lean Bank 1
P0171 means the engine is running too lean on bank 1, often from extra air, not enough fuel, or incorrect sensor data.
P0420 Code: Catalyst System Efficiency Below Threshold
A practical guide to the P0420 check engine code, catalytic converter efficiency, symptoms, causes, and repair cost ranges.
Poor Fuel Economy: Common Causes and Repair Cost
Poor fuel economy can come from driving conditions, maintenance, sensors, fuel mixture problems, or engine faults.
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