O2 Sensor Circuit (Bank 2 Sensor 1)

What it means

The ECU has detected a general fault in the oxygen sensor circuit at Bank 2 Sensor 1. This is the upstream oxygen sensor on bank 2, mounted before the catalytic converter. It measures oxygen in the exhaust so the ECU can keep the fuel mixture correct. Bank 2 is the side of a V6/V8 engine opposite cylinder 1.

Symptoms

• Check engine light on
• Poor fuel economy
• Rough idle or hesitation
• Failed emissions test
• Possible rotten egg smell from a rich mixture

Probable causes

Most likely first

1. 1Failed oxygen sensor (they wear out, typically after 100,000–160,000 km / 60,000–100,000 miles)
2. 2Damaged or melted wiring near the exhaust
3. 3Corroded or loose connector
4. 4Exhaust leak near 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 2 Sensor 1 sensor (in the exhaust manifold or down-pipe, before 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. 4Watch the sensor voltage on live data with the engine warm. A narrowband sensor should switch rapidly between about 0.1 V and 0.9 V (upstream) or hold fairly steady around 0.5–0.7 V (downstream).
5. 5Check for technical service bulletins (TSBs) or software updates for your make and model; some codes have known factory fixes.

Common fixes

• Repair damaged wiring or connector
• Replace the oxygen sensor (use an O2 sensor socket and anti-seize on the threads unless pre-coated)