Oxygen sensors?

[nitro640]

Is there a way to test oxygen sensors?

[Jeremy airjer W]

Yes and no

The easiest way is with a scan tool. Look at O2 sensor data and see what it is doing. Then introduce a vacuum leak and depending on the type of sensor the voltage should drop. Then introduce a rich mixture and the voltage should spike. there are two many variation of the sensor and to many different manufacturer specs to give you a number. This would apply to upstream O2 sensors.

You can backprobe a sensor and watch voltage with a multi-meter set to DC volts. The same scenario above applies. If an upstream sensor is not reacting to rich or lean than it is possibly dead.

[nitro640]

Thanks jeremy. It is an 02 focus. Had it scanned at oreillys got code p0420 catalyst system efficiency below threshold bank 1

[Jeremy airjer W]

It's a catalytic converter. 95% positive it is NOT the O2 sensor.

[FF_205]

I'm with Jeremy on this one, catalytic converter is bad, not doing anything for the exhaust, if you had a scan tool that reads data, the voltage readings from the pre-cat and post-cat o2 sensors will be changing the same, the post-cat sensor readings should be a steady voltage reading when converters are working correctly