Detection Condition
WARNING: This page is about a different car, the 2003 Mazda B4000, 2003 Mazda B3000, and 2003 Mazda B2300. However, it is still accessible from the selected car via links, so may be relevant.
- DTC P0136 indicates output voltage of HO2S12 (rear) fails to meet calibrated limits (bank 1, right cylinder bank).
- DTC P1137 and P1138 indicate HO2S12 (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.
HO2S detects oxygen in the exhaust and produces a variable voltage (0.0-1.1 volts) 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 volt). A low concentration of oxygen in the 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.