What does it mean?
P1154 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: HO2S-21 (Bank 2 Sensor 1) Transition Time Ratio .
Symptoms
- Malfunction indicator lamp on with driveability close to normal
- Long term fuel trims on Bank 2 drifting steadily away from zero
- Small stumble at steady cruise or during gentle throttle changes
- Fuel consumption noticeably worse over a tank
- Readiness monitors not completing after a normal drive cycle
Likely causes
- Sensor element slowed unevenly by age, so one direction of transition lags behind the other
- Deposits from oil, coolant or fuel additives coating the sensing tip
- Exhaust leak near the sensor that only opens up under certain temperatures or loads
- Sensor heater underperforming, letting the element cool during idle
- Poor sensor ground or added circuit resistance rounding the signal edges
- Uneven fuel delivery on that bank from a partially blocked or leaking injector
- Intake leak that appears only at high manifold vacuum
How to fix it
- Record the Bank 2 front sensor waveform at high resolution and measure rise and fall times separately
- Use propane enrichment and a controlled air leak to drive each direction and time the response
- Compare the result with the Bank 1 sensor for a same-vehicle reference
- Smoke test the exhaust under load, not just at idle, to find leaks near the sensor
- Check heater supply voltage, heater resistance and sensor ground quality
- Run an injector balance test on Bank 2 if the trims are skewed
- Replace the sensor once wiring, exhaust and fuel checks pass, then re-run the monitor to confirm