Located in the exhaust system, the Oxygen (O2) Sensor measures the amount of oxygen in the exhaust gases and compares it to the oxygen content in the air. This information is sent to the Engine Control Unit (ECU) to adjust the air-fuel mixture for optimal performance and reduced emissions.
O2 sensors help the ECU maintain the correct air-fuel ratio by signaling when the engine is running rich (too much fuel) or lean (too much air). This constant feedback allows for more efficient combustion, improved fuel economy, and lower emissions.
How It Works:
- The sensor body contains a zirconium dioxide (zirconia) ceramic element, coated with gas-permeable platinum electrodes.
- Exhaust gas contacts one side of the element, while the other side is exposed to outside air.
- The difference in oxygen concentration generates a voltage signal proportional to exhaust oxygen levels.
- The ECU interprets this voltage to adjust fuel injection timing and duration, maintaining efficient combustion and emissions control.
- In heated O2 sensors, a built-in heating element quicklybrings the sensor to operating temperature for accurate readings
even during cold starts.
Product Features & Benefits from Walker Products:
- Improved Engine Response & Performance: Rapid feedback ensures precise air-fuel ratio control.
- Lower Emissions: Optimized combustion minimizes harmful pollutants.
- Improved Fuel Economy: Prevents fuel waste and maintains engine efficiency.
- Longer Sensor Life: Designed with high-temperature ceramic and platinum coatings.
- Meets or Exceeds OEM Specifications: Built to original design and testing standards.
Symptoms of a Failing Oxygen Sensor
- Poor fuel economy (10–15% decrease possible)
- Check Engine Light (MIL) illuminated
- Failed emissions test
- Rough idle, hesitation, or surging
- Premature catalytic converter failure
Preventive Maintenance
- Heated O2 sensors (3- or 4-wire): Replace every 60,000–100,000 miles
- Unheated O2 sensors (1- or 2-wire): Replace every 30,000–50,000 miles
- Check or replace sensors at each major tune-up to prevent catalyst damage and maintain fuel efficiency.
Click here to diagnose types of oxygen sensor contamination.
Where are my oxygen sensors located?
Related Components
Walker Products offers O2 Sensor Bungs & Plugs made in-house from mild steel or stainless steel at our Screw Machine Facility in Fruita, Colorado. We also offer O2 Sensor Sockets and Wrenches designed for ease of installation, and custom bung solutions available individually, in bulk, or in stocking kits.
Common Check Engine Light (CEL) / OBD-II Codes
In accordance with the EPA’s OBD-II standards (adopted in 1996 and later expanded to heavy-duty applications), the following Diagnostic Trouble Codes (DTCs) are commonly associated with Oxygen Sensors.
Use this list as a general reference only. Always consult a qualified technician and follow vehicle manufacturer and EPA guidelines for diagnostics, sensor replacement, and ECU/PCM relearn procedures.
- P0150 – O2 Sensor Circuit Malfunction
- P0151 – O2 Sensor Circuit Low Voltage
- P0152 – O2 Sensor Circuit High Voltage
- P0153 – O2 Sensor Circuit Slow Response
- P0154 – O2 Sensor Circuit No Activity Detected
- P0155 – O2 Sensor Heater Circuit Malfunction
- P0156 – O2 Sensor Circuit Malfunction
- P0157 – O2 Sensor Circuit Low Voltage
- P0158 – O2 Sensor Circuit High Voltage
- P0159 – O2 Sensor Circuit Slow Response
- P0160 – O2 Sensor Circuit No Activity Detected
- P0161 – O2 Sensor Heater Circuit Malfunction
- P0162 – O2 Sensor Circuit Malfunction
- P0163 – O2 Sensor Circuit Low Voltage
- P0164 – O2 Sensor Circuit High Voltage
- P0165 – O2 Sensor Circuit Slow Response
- P0166 – O2 Sensor Circuit No Activity Detected
- P0167 – O2 Sensor Heater Circuit Malfunction
- P0170 – Fuel Trim Malfunction
- P0171 – System Too Lean
- P0172 – System Too Rich
- P0173 – Fuel Trim Malfunction
- P0174 – System Too Lean
- P0175 – System Too Rich