O2 Sensor Circuit Slow Response Bank 1 Sensor 2

Where it lives

For P0139, the sensor sits on the circuit this code reports. The description of P0139 puts it on bank 1.

Check these first

• An aged downstream oxygen sensor on bank 1
• A contaminated downstream oxygen sensor
• An exhaust leak near sensor 2 on bank 1
• Resistance in the bank 1 sensor 2 wiring
• Oil or coolant burning slowing the sensor

What to do next

1. Watch bank 1 sensor 2 switching on a scan tool
2. Check for exhaust leaks near sensor 2
3. Inspect the bank 1 sensor 2 wiring and connector
4. Replace bank 1 sensor 2
5. Confirm there is no oil or coolant burning
6. Clear the code and retest

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