Code P0133 on the 2024 Honda Civic indicates the Bank 1 Sensor 1 (upstream) oxygen sensor is responding slowly to changes in exhaust oxygen content. This sensor is critical for closed-loop fuel control, and slow response degrades the ECM's ability to maintain optimal air-fuel ratio.
Oxygen Sensor Function
The upstream oxygen sensor monitors exhaust gases before the catalytic converter, rapidly switching between rich (high voltage ~0.8V) and lean (low voltage ~0.2V) indications as the ECM adjusts fuel delivery. A healthy sensor switches multiple times per second. Slow response means delayed fuel adjustments.
Slow Response Impact
When the oxygen sensor responds slowly, the ECM receives delayed feedback about combustion. This causes the fuel system to overshoot in both directions - running too rich, then overcorrecting to too lean. Fuel economy suffers and emissions increase even if the engine seems to run normally.
Common Causes
Oxygen sensor aging and contamination are typical causes, but on a 2024 model, actual sensor failure is less likely. Look for exhaust leaks before the sensor that dilute the exhaust sample, oil consumption contaminating the sensor, or wiring issues causing signal degradation. Fuel contamination can also affect sensor response.
Diagnostic Approach
Monitor oxygen sensor signal frequency using a scanner or oscilloscope. A healthy sensor should cross between rich and lean multiple times per second during steady-state driving. Slow switching indicates the sensor or its environment has issues.