Aero1

The A/ F relies on a reference voltage [battery or a 5 volt reference from the PCM]. If This voltage is not very close to battery voltage, with in .2 volts or the 5 volts is off say 4.6 or lower this will be enough to set a code. The same is true for ground. If you put the black on the batt. neg run the car and probe the ground wire with the red pos. lead there should be no more then .05volts better less .02. If ground is bad this will set a code also. This sensor works on heat generator-ed by the sensor as air passes over the heated element the element cools and the resistance changes this is what the cars PCM calculates fuel demand for the engine. I hop this helps Kevin

Hello from N.J. Aero1