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Detection Condition

WARNING: This page is about a different car, the 2002 Mazda Tribute. However, it is still accessible from the selected car via links, so may be relevant.

DTC P1128 indicates during KOER testing the front HO2S signal(s) response for a fuel shift to the correct engine bank was not indicated.

DTC P1129 indicates during KOER testing the rear HO2S signal(s) response for a fuel shift to the correct engine bank was not indicated.

HO2S detects presence of oxygen in exhaust and produces a variable voltage according to the amount of oxygen detected. A high concentration of oxygen in the exhaust produces a low voltage signal (less than 0.4 volt). A low concentration of oxygen in the exhaust produces 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 during closed loop engine operation.

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