Compare a switching oxygen sensor with a wideband air–fuel sensor, then investigate what feedback tells the ECM.
Identify rich versus lean feedback, distinguish upstream narrowband switching from wideband lambda reporting, and explain how closed-loop correction responds to a mixture error.
Conceptual teaching model, not a real sensor electrical circuit or OEM specification. The narrowband trace is illustrative; wideband sensors use dedicated controller circuits and cannot be interpreted as a universal 0–1 V signal. Sensor location, voltage polarity, PID scaling, and closed-loop strategy vary by vehicle.
Move the time slider or play the simulation. The graph shows a short illustrative time window, not a captured waveform.
The upstream sensor indicates a lean exhaust mixture and the ECM is in closed loop. What fuel-trim direction would you normally expect if the feedback is credible?
Choose an answer, then explain what the ECM is trying to correct.
Blue: selected sensor representation (left scale). Amber: ECM correction (right scale). The narrowband trace switches around stoichiometry; its voltage is not a linear air–fuel-ratio meter.
A sensor reports exhaust oxygen information; the ECM uses that feedback along with its control strategy to adjust fueling. A persistent lean indication can reflect a genuinely lean mixture or misleading sensor feedback. Compare fuel trims, operating conditions, related PIDs, exhaust leaks, and independent tests before replacing a sensor.
For a real vehicle, consult OEM diagnostic procedures and the specific sensor and scan-tool PID definitions.