O2 Sensor Signal Stuck Rich (Bank 1 Sensor 2)

What it means

The engine computer tests the downstream sensor during fuel cut-off on deceleration and waits for its voltage to drop. It found that the Bank 1 Sensor 2 signal stayed high (showing rich) anyway. This usually means a contaminated sensor or a circuit fault, and sometimes a real rich mixture.

Related codes: P2270P2273P0138P0172

Symptoms4

• Check engine light on, often with no other symptoms.
• Higher fuel consumption if the mixture is really rich.
• Occasional fuel or sulfur smell from the exhaust.
• Failed emissions test.

Possible causes5

• Downstream sensor contaminated by oil, coolant or silicone.
• Failed or aged downstream oxygen sensor.
• Sensor signal wire shorted to a voltage source, such as the heater wire.
• A real rich mixture from a leaking injector or high fuel pressure.
• Engine computer fault (rare).

How to diagnose5

1. Fix any rich mixture codes such as P0172 first.
2. Watch the downstream sensor voltage on a scan tool while coasting off the throttle; it should drop clearly during fuel cut-off.
3. Check fuel trims; large negative values indicate a real rich condition.
4. Unplug the connector and check the signal wire for a short to voltage.
5. Inspect the sensor tip after removal; white or oily deposits mean contamination and the source must be found.

How to fix5

1. Repair the wire shorted to voltage or the damaged connector.
2. Fix the cause of a rich mixture, such as a leaking injector or faulty regulator.
3. Fix the cause of oil burning or coolant loss if present.
4. Replace the downstream oxygen sensor with a unit that meets the vehicle specification.
5. Clear the codes and drive until the sensor self-test completes.

Repair cost

In Saudi riyals; the highlighted part is the expected range for this fault.

The cost is low for a wire or connector repair, reaches the upper end when the downstream sensor is replaced, and may be more if another cause such as a leaking injector 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