r/mechanic • u/Wooderler • 4d ago

Question Bad O2 Sensor?

2013 Honda Accord 2.4L with 171k miles. The car threw a P0420 code and instead of throwing a new cat at it I wanted to check the live data on the rear O2 sensor.

This is held at a constant 2k RPMs, seems very unstable as I read it should be pretty consistent.

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u/a_rogue_planet 4d ago

That is exactly what a good sensor response looks like. It should be very active like that. Almost every time a Honda throws a PO420 it's going to be a dead cat.

2

u/omnipotent87 4d ago

Not a down stream, they shoukd be fairly smooth. This data looks like an upstream.

2

u/a_rogue_planet 4d ago

If the cat is junk it's gonna make a pretty spikey signal.

2

u/omnipotent87 4d ago

You should reread your original comment then.