O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 3)
The P0166 code indicates that the oxygen sensor located after the catalytic converter on Bank 2 (the side of the engine not containing cylinder #1) is not producing any voltage signal. This sensor monitors the efficiency of the catalytic converter. The PCM detects no activity from the sensor's heater circuit or signal circuit, often due to a faulty sensor, wiring issues, or a blown fuse.
01. Most Common Causes
- Faulty oxygen sensor (Bank 2 Sensor 3)
- Open or shorted wiring in the sensor circuit
- Blown fuse for the oxygen sensor heater circuit
- Corroded or damaged connector
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Failed emissions test
- Possible decrease in fuel economy
- No noticeable drivability issues in most cases
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm the code and check for other codes.
Step 2: Visually inspect the sensor and wiring for damage, corrosion, or loose connections.
Step 3: Test the sensor's heater circuit with a multimeter for proper resistance and voltage.
Step 4: If wiring and fuses are good, replace the oxygen sensor.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
Yes, it is generally safe to drive short distances, but the vehicle may fail an emissions test and fuel economy could suffer. It's best to repair it promptly.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for the sensor and labor, depending on vehicle make and model.