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Rear O2 Sensor False Reading?


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5 replies to this topic

#1 jonfit04

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Posted 23 October 2006 - 01:45 PM

Ok,

I have had my CEL on for a while now, so I went to Autozone and had them read the code. The guy said all that he can tell me is that the rear 02 sensor was giving a "false" code. What does that mean. My car occasionally when driving starts to sort of bogg down, and when you hit the gas it gets worse, but when I let off and take it slow it goes back to normal. I think it might retard the timing, it did the same thing when the Knock sensor failed. So I know I have 2 o2 sensors (front and rear). Which should be replaced.? Need some guidance?

#2 porcupine73

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Posted 23 October 2006 - 02:21 PM

If you're going to replace an O2 sensor, I'd start with first if you don't know when it was last replaced. That is the one used for the air/fuel ratio control loop after it's hot enough (typically a few minutes after startup). Anywho, the rear is typically used only to determine if there's issues with the catalytic converter which might make you not pass emissions inspection depending on your state.

What you want to know is the exact code autozone pulled (i.e. P0123 or whatever). If the code reader gives a description, it's the generic ODBII description, but with the code you can find out exactly what Subaru says about it. P1abc codes are manufacturer specific.

There are other sensors issues that can cause the symptoms you described.

#3 jonfit04

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Posted 25 October 2006 - 05:44 AM

If you're going to replace an O2 sensor, I'd start with first if you don't know when it was last replaced. That is the one used for the air/fuel ratio control loop after it's hot enough (typically a few minutes after startup). Anywho, the rear is typically used only to determine if there's issues with the catalytic converter which might make you not pass emissions inspection depending on your state.

What you want to know is the exact code autozone pulled (i.e. P0123 or whatever). If the code reader gives a description, it's the generic ODBII description, but with the code you can find out exactly what Subaru says about it. P1abc codes are manufacturer specific.

There are other sensors issues that can cause the symptoms you described.

Thanks for your reply, I plan to drive down to autozone and check and see if they can give the specific code, but I would agree to change the first as well. I've read they are the usual suspects. You said "There are other sensors issues that can cause the symptoms you described". Like what? Anything else I should check?

#4 porcupine73

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Posted 25 October 2006 - 11:23 AM

Other sensors for that kind of driveability issue could maybe include MAF or MAP, knock sensor, and maybe even engine coolant temp sensor. But first you need to know what the P code is that is causing the check engine light to come on.

#5 jonfit04

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Posted 25 October 2006 - 11:41 AM

Other sensors for that kind of driveability issue could maybe include MAF or MAP, knock sensor, and maybe even engine coolant temp sensor. But first you need to know what the P code is that is causing the check engine light to come on.

Again thanks!, I am going down first thing tomorrow to autozone, and have them see if they can get the exact code, just out of curiosity. If it was another one of the sensors you listed, would they also give off a code. I know the Knock sensor does, Have had that happen already, but would the others? I just got in it to go out to lunch and heres what happens.... Its drives, but it has no power. you hit the gas and it just goes slowly up in speed and RPM then it starts to sort of jerk "lightly" and the power comes back after a about 2 miles. but then it does it again, I am going about 35mph and when I hit the gas to speed up...nothing!...just sluggish....thats the best I can describe....any thoughts?

#6 porcupine73

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Posted 25 October 2006 - 06:32 PM

The next step is to get the exact code of the code reader. Don't settle for them telling you the description of the code that the reader gives, you want the number like P0123. Trying to do anything else without knowing that code is putting the proverbial cart before the horse.




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