O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)

What it means

The oxygen sensor at Bank 1 Sensor 2 is reading high voltage (rich) for longer than expected. This is the downstream oxygen sensor on bank 1, mounted after the catalytic converter. Its main job is to check that the converter is working.

Symptoms

• Check engine light on
• Usually no change in how the car drives
• Failed emissions test
• Catalyst monitor not completing

Probable causes

Most likely first

1. 1Signal wire shorted to voltage (often the heater wire inside a damaged harness)
2. 2Failed or fuel-contaminated oxygen sensor
3. 3Coolant or oil contaminating the sensor

How to diagnose it

Work through these in order before buying parts

1. 1Record the code and its freeze frame data (speed, load, temperature when it set), then clear it and see if it comes back.
2. 2Locate the Bank 1 Sensor 2 sensor (in the exhaust pipe just after the catalytic converter). Inspect the connector and wiring; exhaust heat often melts or chafes these wires.
3. 3Check for exhaust leaks ahead of the sensor (ticking noise, soot marks). Outside air pulled in through a leak makes the sensor read lean.
4. 4Unplug the sensor with the key on: the ECU side of the signal wire should read about 0.45 V or less. A higher reading means a short to voltage in the harness.
5. 5Check fuel trims; strongly negative trims point to a real rich condition.
6. 6Check for technical service bulletins (TSBs) or software updates for your make and model; some codes have known factory fixes.

Common fixes

• Repair shorted wiring
• Replace the oxygen sensor
• Fix the cause of a rich mixture before fitting a new sensor, or it will be contaminated again