P0133

DESCRIPTION
The Engine Control Module (ECM) uses oxygen sensor signals to maintain the air fuel mixture at the ratio resulting in optimum fuel economy and reduced emissions. The amount of oxygen in the exhaust gases indicates, to the front oxygen sensor, whether the air fuel mixture being supplied to the engine cylinders is rich or lean. The readings of the rear oxygen sensor are used to indicate the efficiency of the catalytic converter. The ECM calculates catalytic convener efficiency by comparing the rear oxygen sensor signal to the front oxygen sensor signal. A normal oxygen sensor signal will constantly fluctuate above and below 500 mV, with the front oxygen sensor signal frequency of at least 5 Hz at 2500 rpm. Due to the effect of the catalytic converter, the rear oxygen sensor signal frequency will be lower than the front oxygen sensor signal frequency. If the rear oxygen sensor signal coincides with the front oxygen sensor signal a large percentage of the time, this indicates a loss in efficiency of the catalytic converter or a malfunction within the fuel system.






FAILURE CONDITIONS
The ECM will set P0133 and MIL will turn on if the ECM does not sense the following condition during two driving cycles:

1. Over a period of 2.3 seconds, the ECM must sense a series of 10 crossovers (lean to rich or rich to lean) when:
- Engine RPM is between 2000 and 3000 RPM.
- Engine load range is between 1.9 and 4.7 milliseconds. Catalyst temperature is above 356 °C (673 °F).
- System is in closed loop.

2. The ECM must make some correction within 133 seconds in the air/fuel ratio when:
- Engine RPM is between 1600 and 2400 rpm. Engine load range is between 1.35 and 1.8 milliseconds.
- Catalyst temperature is above 356 °C (673 °F).
- System is in closed loop.

This code indicates the engine air fuel ratio is not being adjusted by the front oxygen sensor signal or the ECM as expected to do so, or not adjusted as often as expected to do so, once the engine is warmed or under normal engine use.

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TEST PROCEDURE