Locate the oxygen sensor on the exhaust system
Inspect the sensor and wiring for damage, corrosion, or loose connections
Check for trouble codes with an OBD-II scanner
View live sensor data on the scanner
Start the engine and let it reach operating temperature
Observe the sensor voltage or air-fuel ratio readings
Verify the readings switch or fluctuate as the engine runs
Raise engine speed and confirm the readings respond quickly
Check for heater circuit resistance with a multimeter if needed
Test the sensor signal wire with a multimeter if needed
Compare readings to manufacturer specifications
Replace the sensor if readings are slow, stuck, or out of range