O2 Sensor Circuit Slow Response (Bank 2 Sensor 1)

What it means

The engine computer has found that the bank 2 upstream oxygen sensor switches slowly between rich and lean, slower than the manufacturer limit. This usually points to an aged or contaminated sensor, and fuel control on that bank gradually becomes less precise.

Related codes: P0150P0133P0174P0430P0155

Symptoms4

• Check engine light on.
• Gradual increase in fuel consumption.
• No clear driving symptoms in many cases.
• Failed emissions test.

Possible causes5

• Aged bank 2 upstream oxygen sensor.
• Sensor contaminated by engine oil or coolant, for example from a head gasket leak on that bank.
• Leak in the bank 2 exhaust manifold ahead of the sensor.
• Weak sensor heater.
• Extra resistance in the connector or wiring.

How to diagnose5

1. Compare the switching speed of the bank 2 sensor with the bank 1 sensor at steady speed; a clear difference points to an aged bank 2 sensor.
2. Remove the sensor and check its tip for white or black deposits that indicate contamination.
3. Check the bank 2 exhaust manifold for leaks.
4. Make sure there is no heater code such as P0155 or mixture codes on bank 2.
5. Inspect the connector and wiring for corrosion.

How to fix5

1. Repair any exhaust leak.
2. Clean the connector or repair the wiring.
3. Fix the source of oil or coolant contamination if found.
4. Replace the bank 2 upstream oxygen sensor.
5. Clear the codes and drive until the self-test completes.

The cost is usually the sensor plus fitting, rising if it is hard to reach behind the engine or an exhaust leak is found.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions