Detection Condition
WARNING: This page is about a different car, the 2003 Mazda Tribute. However, it is still accessible from the selected car via links, so may be relevant.
- DTC P0136 indicates output voltage of HO2S-12 (rear) fail to meet calibrated limits (bank 1).
- DTC P0156 indicates output voltage of HO2S-22 (rear) fail to meet calibrated limits (bank 2).
- DTCs P1137, P1138, P2270 and P2271 indicate HO2S-12 (rear) is forced rich and lean by PCM. The test fails if PCM does not detect a rich signal (P1137 and P2270) or lean signal (P1138 and P2271) during KOER self-test (Bank 1).
- DTCs P1157, P1158, P2272 and P2273 indicate HO2S-22 (rear) is forced rich and lean by PCM. The test fails if PCM does not detect a rich signal (P1157 and P2272) or lean signal (P1158 and P2273) during KOER self-test (Bank 2).
HO2S detects oxygen in exhaust and produces a variable voltage (0.0-1.1 volt) according to the amount of oxygen detected. A high concentration of oxygen in exhaust causes HO2S to produce a low voltage signal (less than 0.4 volt). A low concentration of oxygen in exhaust causes HO2S to produce a high voltage signal (more than 0.6 volt). HO2S provides feedback to PCM indicating air/fuel ratio in order to achieve near stoichiometric air/fuel ratio of 14.7:1 during closed loop engine operation.