O2 Sensor behind CAT Out

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Old 04-12-2006, 09:02 PM
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O2 Sensor behind CAT Out

I know how to fix the problem, here's the question.

Will not dealing with this immediately have any detrimental effects on my engine. Will the computer overcompensate to a 'safe level' and run a overly rich mixture, or does this O2 sensor just act as a monitor for engine efficiency and combustion makeup?

Essentially, will the ECU change the combustion mix parameters due to a bad O2 sensor?
Old 04-12-2006, 10:53 PM
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Will not dealing with this immediately have any detrimental effects on my engine.
The ECU uses the Oxygen sensor to get a reading of data so that it can make suitable adjustments to the fuel map.
If it can't get a reading of the current data, Id assume it has to have somekind of default data(safe level) that the factory programmed into the first place, and it would use that until the problem is corrected like get a new sensor(to get the most current data again).

So to answer your question, I would assume you may get a richer mixture thus get bad milege. Now if I can only change the default mixture in the software to my own, it would make my life alittle easier.
Old 04-13-2006, 07:30 AM
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Old 04-13-2006, 08:01 AM
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I'm almost positive that the ECU turns to a "safe mode" fuel map where it runs rich
Old 04-13-2006, 07:14 PM
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If you have a defective O2 sensor BEHIND the catalytic converter, it will not affect the fuel flow control for the engine. The rear O2 sensor monitors catalytic converter efficiency only. I assume you have a O2 sensor heater code on the rear sensor. It's difficult to diagnose a faulty sensor otherwise.

Codes P0420 and P0430 indicate the catalytic converter efficiency is not in line w/ expectations, usually the O2 level is moving up and down in line w/ the O2 sensor ahead of the cat. Other things besides a failing cat can cause these codes such as poor combustion or leaks in exhaust manifold.

I had P0420 on a 99 Subaru and simply reset the ECU and code did not return, although the O2 level suggests the cat is not working correctly. OEM cats are very expensive and you want to be dead sure of a bad coverter before replacing.

good luck
Old 04-14-2006, 12:39 AM
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The error was P0141, which was in fact a heater malfunction. Can the scanner actually reset the error?
Old 04-14-2006, 06:13 AM
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Yes, scanner will reset. However, that code will likely again appear immediately upon restarting the car.

good luck
Old 04-14-2006, 06:34 AM
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that happened on my cressida where my O2 sensor went bad and turned on my check engine light... it would cause the engine to run super rich...
Old 04-14-2006, 05:46 PM
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Sorry if Im thread jacking, but I also got code P0141 from my scanner. The details said O2 sensor in bank 1. Where is bank 1?- Is it on the driver or passenger side? Thanks
Old 04-14-2006, 08:47 PM
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Originally Posted by bustardvan
Sorry if Im thread jacking, but I also got code P0141 from my scanner. The details said O2 sensor in bank 1. Where is bank 1?- Is it on the driver or passenger side? Thanks
Bank 1 contains cylinder #1. I assume you have a 3.2. I'm not sure which side has cyl 1, but it's usually embossed on the intake manifold somewhere.

good luck
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