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Discussion Starter #1
SES light is on and I ran the code and got P040 which is the driver side Cat not being efficient. I did some searching on here which was concerning since it doesn't really seem like there is an obvious fix. I was reading that people have replaced Cat's, 02 sensors, etc and it's still possible for the SES light to come back on.

I don't really want to drop a lot of money into a new cat if it's not going to fix the problem. Just looking for advice on what route I should go. Just got the truck and so far the gas mileage has been down around 13 so I was just curious if maybe my motor is running rich? Any suggestions?
 

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Discussion Starter #3
No I haven't noticed any smoke. My plan is to probably reset the SES and check the spark plugs. If it comes on again replace the O2 sensor and if it comes on again after that look into replacing the cat.
 

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Or, reset it and see if it comes back.


I got that code about 2 months ago, bought the reader for 50 and reset it. Haven't seen it again!


On other forums there is speculation that unless it comes in HARD and stays, its just a fluke in the ECU software and the sensors. That is what I am seeing.

IMHO YMMV.
 

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From what I understand the rears won't throw a code. If the cats drop below 95% efficiency the front O2's will send a code. Another possible fix is to install spark plug anti foulers on the O2 sensor, then screw them back in. Takes the sensor out of direct path of exhaust.
Good luck
 

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From what I understand the rears won't throw a code. If the cats drop below 95% efficiency the front O2's will send a code. Another possible fix is to install spark plug anti foulers on the O2 sensor, then screw them back in. Takes the sensor out of direct path of exhaust.
Good luck
It is the rear O2s that measure cat efficiency so yes, they do throw the code (fronts are pre-cat so there's no way they can measure them). The fronts measure AFR and control the engine, the rears check to make sure all the fuel is gone.

The anti-foulers should work if the rear O2 is in fact bad. But you put it on the rear, not the front. If you put it on the front the O2 would read lean all the time and the engine would compensate by adding more fuel (rich). This is why I said front. It happened to me once.

The poster didn't mention his model so I don't know if its single or dual exhaust pipes. But, if it is dual, it actually makes things easier (and cheaper) to diagnose.
Swap the two front sensors. If the code follows the sensor then its the sensor.
If it doesn't follow, swap the rear sensors, If the code follows the sensor then its the sensor. If it doesn't, then its the CAT.

"Finally" is correct. There are other possibilities that can set the code. A tank of questionable gas for instance. So the first step should be to clear the code and see if it repeats.

EDIT:
BJAR, I'll be watching for a white Fronty on the roads. Oh, wait a minute. How do I know its a white truck?
I saw his welcome post. :)
So its a 2005 Nismo, does that make it dual exhaust?
 

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Discussion Starter #9
That’s a lot of great information, thank you! The Nismo just has he same exhaust as other models correct? Probably a Y-pipe. I haven’t even looked at it yet.

Where you located GotToGo? I live and work over in the Glenwood area.


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Ustick.

Is it a V6 or straight?

If its a V I'd guess that it has 2 sets of sensors. But I'm not familiar with these models, at all.

If there is a front sensor on each pipe then your on easy street.
 

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It is the rear O2s that measure cat efficiency so yes, they do throw the code (fronts are pre-cat so there's no way they can measure them). The fronts measure AFR and control the engine, the rears check to make sure all the fuel is gone.

The anti-foulers should work if the rear O2 is in fact bad. But you put it on the rear, not the front. If you put it on the front the O2 would read lean all the time and the engine would compensate by adding more fuel (rich). This is why I said front. It happened to me once.

The poster didn't mention his model so I don't know if its single or dual exhaust pipes. But, if it is dual, it actually makes things easier (and cheaper) to diagnose.
Swap the two front sensors. If the code follows the sensor then its the sensor.
If it doesn't follow, swap the rear sensors, If the code follows the sensor then its the sensor. If it doesn't, then its the CAT.

"Finally" is correct. There are other possibilities that can set the code. A tank of questionable gas for instance. So the first step should be to clear the code and see if it repeats.

Thanks for correcting me. I always learn here.
 

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Discussion Starter #12
Reset the service engine soon light last week and it came back on today. Anybody replace their cat with an aftermarket like a maganaflow and have any luck?


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Reset the service engine soon light last week and it came back on today. Anybody replace their cat with an aftermarket like a maganaflow and have any luck?

I used a Walker direct fit primary cat on the driver side still going fine. The dealer replaced my passenger side cat with am OE cat and it is throwing a code now.
 
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