Question

P1138 Lack Of HO2S12 Switch - Sensor Indicates Rich
what is this ?

Answer 1

Hi there,

As the O2 sensor reads the amount of O2 in the exhaust the voltage fluxuates. This is called a switch. The code indicates that the O2 sensor isn't happy and that the engine is running rich. Sometimes this can be the result of some type of engine issue. A misfire for example would cause a rich reading on the O2 sensor because raw fuel would be going into the converter. The most common cause for this code is either a bad converter or bad rear O2 sensor.