P2198Powertrain
Powertrain · SAE
O2 Sensor Signal Stuck Rich — Bank 2, Sensor 1
Meaning
The upstream lambda sensor on bank 2 persistently reports a rich mixture signal without the typical oscillations of closed-loop control. The ECU applies maximum negative fuel trim without achieving stoichiometry on bank 2.
Common causes
- Faulty or contaminated O2 sensor B2S1 (signal stuck rich, > 0.7 V)
- Leaking or over-fuelling injectors on bank 2
- Excessive fuel pressure
- Faulty MAF sensor reporting insufficient airflow
- EVAP fault causing excessive purge vapour
- Fuel pressure relief valve leaking (diesel)
Symptoms
- Check engine light (MIL) on
- Bank 2 long-term fuel trim (LTFT) strongly negative
- Raw fuel smell from exhaust
- Increased fuel consumption
- Possible black smoke
Severity
Moderate to high: a chronically rich mixture on bank 2 damages the catalyst and may cause oil dilution.
What to do
- Read bank 2 STFT/LTFT fuel trims to confirm rich tendency
- Check fuel pressure and bank 2 injector condition (static leak-down test)
- Monitor O2 sensor B2S1 signal in real time: absence of oscillations indicates faulty sensor
- Check EVAP system for abnormal purge
- Replace O2 sensor B2S1 if signal is persistently rich