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Discussion Starter · #1 ·
Hey guys, this is for a 2010 Impreza non-wrx, our daily car.

A while ago it started giving us the p0420 cel, we know this car has an exhaust leak before the first o2 sensor (loud enough for any pedestrians to hear that driving by at 5mph).

When we plug in the obd2 we got 2.0v for o2b1s1 (is that even normal?) does that mean the first o2 sensor is bad or could be just the exhaust leak.
And for o2b1s2 it jumps around all over the place, does that mean our cat is bad?

Any suggestions would be great, much appreciated.
 

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You have a leak before the upstream o2? You need to fix that now
 

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Your ECU needs correct data to ensure your car is getting the right amount of fuel. A leak can cause serious problems including errors from the rear o2
 

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Discussion Starter · #5 ·
Your ECU needs correct data to ensure your car is getting the right amount of fuel. A leak can cause serious problems including errors from the rear o2
Oh okay I was under the impression that it would only make the car runs richer but yeah you're right, I should probably fix that first before determining if any else is wrong. Thanks btw
 

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That's not any better than lean, it fouls plugs and causes carbon buildup in the cylinder.
 

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Probably not, it's likely part of what is throwing a rear o2 code. Running rich will total a cat quickly
 
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