O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)

What it means

The engine computer has seen the downstream oxygen sensor voltage on bank 1 stay above the allowed limit, even when it should drop, such as during fuel cut on deceleration. The usual cause is a failed sensor or a short feeding voltage into the signal wire, and sometimes a truly rich mixture.

Related codes: P0136P0137P2271P0172P0141

Symptoms4

• Check engine light on.
• Engine usually runs normally.
• Fuel smell from the exhaust if the mixture really is rich.
• Failed emissions test.

Possible causes5

• Internal failure of the downstream oxygen sensor.
• Signal wire shorted to the heater supply or another voltage source.
• Moisture or corrosion inside the connector.
• A real rich mixture from a leaking injector or high fuel pressure.
• Engine computer fault (rare).

How to diagnose5

1. Watch the downstream signal when lifting off the accelerator at speed; the voltage should drop during fuel cut.
2. Unplug the connector; if the reading stays high with no sensor, the fault is in the wiring or computer.
3. Inspect the connector for water or corrosion.
4. Check the upstream fuel trims to rule out a real rich mixture.
5. If all of the above is fine, the sensor is the cause.

How to fix4

1. Clean and dry the connector and repair any shorted wires.
2. Replace the downstream oxygen sensor if its voltage stays high during fuel cut.
3. Fix the cause of a rich mixture if found.
4. Clear the codes and drive until the sensor and converter tests complete.

Repair cost

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

Cleaning a connector or repairing a wire costs little; a new sensor is the most common fix, and the cost rises if a rich mixture needs injector repair.

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