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Q: O2 sensors

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I have a Toyota 4 runner, o2 sensors, #1 both banks are reading 3.25+ volts, would the sensors be bad or should I start looking father upstream? MAF, etc?

My car has 111000 miles.
My car has an automatic transmission.

A: Oxygen sensors don’t work in that voltage r...

Oxygen sensors don’t work in that voltage range. Oxygen sensors range from .1 to .9 volts. When the vehicle is running normal the sensor ranges between .4 to .6 volts. The O2 voltage should change constantly going above and below .5, these are called cross counts. A voltage reading stuck above .5 volts is considered rich in fuel, a reading stuck below .5 is considered lean in fuel.

Rich conditions can be caused by many things like leaking injectors, or a cylinder not working properly for example. Lean conditions are usually caused by vacuum leaks.

While I’m not sure what reading you’re looking at, I am guessing that it is possibly the fuel trim. I suggest seeking help from a qualified mechanic to help you correctly identify your issue and replace your oxygen sensors if needed.

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