O2 readings

**Progas** · 11-07-2008

I finally got my HP tuner, and decided to do some scanning before I do anything. Well I scanned my car all the way to work (about 70mi), and then reran the saved scan. I noticed my O2 sensor is all over the place. It oscillates like a sine wave. It goes from about 63mV to 850mV back and forth really fast. Is this normal? I thought the O2 would read relatively steady dependant upon throttle.

I dont have a check engine light on either. I have not scanned for codes yet not sure I will find anything if I do.

**Scimmia** · 11-07-2008

Yes, this is totally normal for cruising at part throttle. The computer adjusts until you go lean, then adjusts it until you go rich, so it keeps going back and forth.

TDCRacing · 11-08-2008

Yeah it's normal. The only time the o2's will lock in is when you go into PE. Wich is at about 35% TPS on a stock PE vs. TPS table.

**Progas** · 11-08-2008

Thanks for the replies

I guess I just always assumed the computer would compensate faster than that, and hold a more steady reading. I will check the log when it was in PE mode, and see what it showed. I thought maybe the sensor was bad.

TDCRacing · 11-08-2008

When the sensor is bad or even a wire has melted on the exhaust or has been cut they usually read a fairly steady reading all the time. Then you will get an slow switching code or something like that

**Sabrewings** · 11-08-2008

Originally Posted by Progas

I guess I just always assumed the computer would compensate faster than that, and hold a more steady reading.

It's not that it can't compensate fast enough. That's how it tests the sensor's operation, by swinging it back and forth to make sure it responds appropriately.

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