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Registered
2001 Forester
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1,140 Posts
Discussion Starter #1
I don't remember the code :icon_redface: but I do remember that my bank 1 front o2 sensor is on it's way out. We are leaving for a trip to the beach tomorrow morning so there is nothing I can do about it I guess but I was wondering if it would be a problem making a 3 hour trip with an o2 sensor on the way out. I feel like if anything, it will just run a bit rich and my gas mileage won't be optimal.

Thanks in advance.
 

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The Modfather
2019 Impreza 5dr Sport - Manual
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8,052 Posts
Depends on how bad it is I suppose. Your thinking is correct that you will most likely just use more gas.
 

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Registered
2005 Impreza RS Wagon Auto
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3,658 Posts
If the sensor completly fries from the heat of a long trip you will be SOL. Without the sensor working at all your engine will stumble and most likely stall. If it's just becoming inaccurate, then you'll def use more gas than normal.
 

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Official sf.org decal guy
2006 FXT
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12,367 Posts
What exactly does the front O2 sensor do compared to the rear? I just had to replace my rear O2. The car seems to run smoother but I wonder if that's just me. The only noticeable result of the bad O2 was a CEL. What do each of them do?
 

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Administrator
2007 Forester Sports XT 4EAT
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38,754 Posts
The front O2 sensor, or Air/Fuel sensor monitors the amount of oxygen in the exhaust gases and provides the "feedback" signal to the ECM. If the sensor senses high level of oxygen, the engine is running too lean (not enough fuel). The ECM adds more fuel. If the level of oxygen in the exhaust is too low, the ECM decides that the engine is running too rich (too much fuel) and subtracts fuel accordingly. As you can see, the front O2 sensor is critical for correct engine operation.

The rear O2 sensor monitors the efficiency of the CAT. That's where the P0420 CEL code comes from. :wink:

Bobby...

['07 FSXT MODding Journal] ['03 X MODding Journal]
 

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Registered
2001 Forester
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1,140 Posts
Discussion Starter #7
Guess I'll just keep my fingers crossed. I'll get it taken care of when I get back.
 

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Registered
02 Forester L (sold) Manual
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1,220 Posts
My front one threw a code after I touched it (yeah, really), car ran the same for a couple weeks until I could get it replaced.
 

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The Modfather
2019 Impreza 5dr Sport - Manual
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8,052 Posts
My front one went bad in my 99 RS. What happened to me as the sensor starts to go bad was the MPG's started to slowly drop. They went from around 28 to 16 over about 2-3 months. I began to notice a more than usual amount of carbon black on the tail pipe. Eventually I would get a slight stumble upon acceleration. The stumble would happen after a particular amount of time. I imagine the exhaust temps. got to a particular level. Soon the hesitation would happen more often and then I would get a CEL that would stay on till the car cooled down and would go away. I'm not saying this will happen in every case but what happened to me. I changed the sensor and my car ran fine again and MPG's went back to normal. When I changed the front sensor in my Forester after it had about 70K miles my MPG's went up about 2-3 more on average. Same for my Miata. I changed the two front ones on our Tribeca after 60K (more as a PM) and it made no difference.
 
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