O2 Sensors

WildWilly · Jun 16, 2016

Hey yall,

I'm getting a code for P0138. Looking that up shows that it's the O2 sensor behind the cat. Been noticing that my fuel economy has gone down a bit, but I know that's also to expect with an older truck. If I replace it, could that help fix that?

Only thing I wasn't sure of was that the fact that we've punched out my cat if I'd have to do anything additionally to fix that second 02 sensor?

joepizuro · Jun 18, 2016

Code should explain better. Sounds like your o2 sensor after the cat is telling your computer the cat is malfunctioning (because you punched it out). Try pulling the o2 sensor out of the pipe so it gets fresher air and unplug the battery for a while and see if it comes back.

Yeret · Jun 18, 2016

The rearward O2 sensor is just used as a reference for the computer to determine if the catalytic converter is working or not. If the cat is functioning correctly, there will be a difference in output voltage between the two O2 sensors.

The rear O2 sensor has no effect on fuel economy. Trust me, I drove my truck for months without one when I first had exhaust work done and the guy couldn't remove it from the old pipe. My fuel economy was actually at it's highest.

You've punched the catalytic and at first I thought that your code was going to be "catalyst efficiency below minimum threshold" or something. Actually, looking it up, it looks like you've either got a faulty O2 sensor (if you're lucky) or a short (if you're not lucky).

I wouldn't be surprised if you replaced the O2 sensor and then later get a code for the catalytic itself.

O2 Sensors

WildWilly

Senior Member

joepizuro

Senior Member

Yeret

The Village Drunk

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