p0125, running rich, bad 02 sensor?

98mitsubishigst · Aug 11, 2013

Every so often my car will stop running like its normal, awesome self, and it will run like crap..

Its about every couple hundred miles it does this issue, and normally if i turn the car off and i don't drive it for a few hours, the issue goes away.

MY ISSUE I AM HAVING IS: -- Sometimes i will be driving and the car will just peg rich. It'll hover around 10-12 on my wide band and stay in the green.. and at idle my hks 272 cams will stop lopeing and the car when driving will feel sluggish. Normally the car will cruise around 15-16 BUT when the car has this issue it just runs rich..

I threw a code today when driving down the road with this issue, P0125, and i read it's coolant sensor related, and it also can be o2 sensor related.. My o2 sensor is mighty beat up some how.. I heard when a o2 sensor goes out, the computer will make the car run rich to kind of make the car run in a "safe" mode.. Is this true?

Anyway, what do you guys think it is??

ChiTownHussla · Aug 11, 2013

little searching would help.. but I am not a mod so here.

http://www.dsmtuners.com/forums/maintenance-repairs/361838-p0125-code-no-resolve-so-far.html

zach4gt · Aug 11, 2013

Yes its true what happens is the o2reads that there is to much air coming through the exhaust which tells the pcm to add more fuel

First check the 02 with a voltmeter it should read around one volt make sure not on the heater circuit when doing this

Zack Huffman · Aug 11, 2013

zach4gt said:
Yes its true what happens is the o2 reads that there is to much air coming through the exhaust which tells the pcm to add more fuel

The sensor sends low voltage when it's dying. Low voltage corresponds to a lean condition (read: too much post-combustion oxygen is present compared to ambient). Fuel trims trying to correct by adding fuel with no resulting change in O2 sensor output means you run richer and richer until the fuel trims max out.

First check the 02 with a voltmeter it should read around one volt make sure not on the heater circuit when doing this

Should see it swinging quickly between 0.2 and 0.8 volts actually. If it sits around 0.3 volts or less for more than a few seconds it's pretty likely a dead sensor. At 0.5 volts is 14.7 AFR on gasoline, -everything else is inaccurate on a binary (narrowband) O2 sensor's response curve.

OP, after you verify that there's still coolant in the bottom of your overflow bottle, the CTS is the next place to check. After that, then bust out the logger and watch the O2 signal.

zach4gt · Aug 11, 2013

Sorry about that I'm going to school for all that and forgot about it switching back and forth and that most o2s max out at 1 volt

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p0125, running rich, bad 02 sensor?

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