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Circuit Description

The powertrain control module (PCM)/engine control module (ECM) constantly monitors oxygen sensor (O2S1) activity for 100 seconds. During monitor period, PCM/ECM counts number of times that O2S1 switches from rich to lean and from lean to rich. With this information, a total for all switches can be determined. If number of switches is too low, DTC P1133 will set. The lean-to-rich and rich-to-lean are greater than 20 switches.