The powertrain control module (PCM) supplies a bias voltage of about 450 mV between the heated oxygen sensor (HO2S) high signal circuit and the HO2S low reference circuit. When measured with a 10 mega ohm digital voltmeter, this may display as low as 350 mV. The oxygen sensor signal varies from about 800 mV when the exhaust is rich, to about 50 mV when the exhaust is lean.

If the HO2S 1 voltage remains at or near the 450 mV bias for an extended period of time, DTC P0134 is set. If the signal amplitude of HO2S bank 1 sensor exceeds the no activity (P0134) thresholds but will not allow closed loop operation, DTC P0130 will set.

If the HO2S 1 voltage remains excessively low for an extended time, DTC P0131 will set.

If the HO2S 1 voltage remains excessively high for an extended period of time, DTC P0132 will set.

During the monitoring period, the PCM counts the number of times that a rich-to-lean and lean-to-rich response is indicated and adds the amount of time necessary to complete all transitions. With this information, an average time for each transition can be determined. If the average response time is too slow, a DTC P0133 will be set.

If the HO2S 1 voltage remains at or near the 450 mV bias for an extended period of time, DTC P0134 is set.

If the HO2S 2 signal voltage remains excessively low for an extended period of time, DTC P0137 will set.

If the HO2S 2 voltage remains excessively high for an extended period of time, DTC P0138 will set.

If the HO2S 2 voltage remains at or near the 450 mV bias for an extended period of time, DTC P0140 will set.

If the PCM determines that too much time was required for the HO2S 2 to become active, DTC P0141 will set.

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