Detection Condition

DTC P0136 indicates output voltage of HO2S-12 (rear) fails to meet calibrated limits (bank 1).

DTC P0156 indicates output voltage of HO2S-22 (rear) fails to meet calibrated limits (bank 2).

DTC P1137 and DTC P1138 indicate HO2S-12 (rear) is forced rich and lean by PCM. The test fails if PCM does not detect a rich signal (P1137) or lean signal (P1138) during KOER self-test (Bank 1).

DTC P1157 and DTC P1158 indicate HO2S-22 (rear) is forced rich and lean by PCM. The test fails if PCM does not detect a rich signal (P1157) or lean signal (P1158) during KOER self-test (Bank 2).

HO2S detects oxygen in the exhaust and produces a variable voltage according to the amount of oxygen detected. A high concentration of oxygen in the exhaust causes HO2S to produce a low voltage signal (less than 0.4 volts). A low concentration of oxygen in the exhaust causes HO2S to produce a high voltage signal (more than 0.6 volts). HO2S provides feedback to PCM indicating air/fuel ratio in order to achieve near stoichiometric air/fuel ratio during closed loop engine operation.