P2197Powertrain
Powertrain · SAE
O2 Sensor Signal Stuck Lean — Bank 2, Sensor 1
Meaning
The upstream lambda sensor on bank 2 persistently reports a lean mixture signal without the expected closed-loop oscillations. The ECU cannot bring bank 2 to stoichiometry despite positive fuel trim corrections.
Common causes
- Faulty or contaminated O2 sensor B2S1 (signal stuck at lean value)
- Air leaks downstream of the MAF on the bank 2 side
- Clogged or low-flow injectors on bank 2
- Low fuel pressure (common to both banks)
- Faulty MAF sensor reporting excessive airflow
- EVAP system leak
Symptoms
- Check engine light (MIL) on
- Bank 2 long-term fuel trim (LTFT) strongly positive
- Possible power loss or stumble on acceleration
- Possible rough idle
- Elevated HC emissions at test
Severity
Moderate to high: like P2195 for bank 2, a chronically lean mixture risks knock, elevated temperatures, and long-term engine damage.
What to do
- Read bank 2 STFT/LTFT fuel trims to confirm lean tendency
- Check for intake air leaks on the bank 2 side downstream of the MAF
- Measure fuel pressure at idle
- Monitor O2 sensor B2S1 in real time: absence of oscillations indicates a faulty sensor
- Check bank 2 injector flow balance