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Forums Nissan Models Sentra P0420 catalyst system efficiency below threshold bank 1
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Old 09-28-2010, 07:44 PM
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Default P0420 catalyst system efficiency below threshold bank 1

Ok, so I replaced my exhaust(pipes, converter, Rear o2 Sensor, Muffler) after road debris ripped out my old o2 sensor. All the flanges were crumbling and there were holes,.....everything was replaced.

I cleared the check engine light by leaving my batt lead disconnected overnight. Then I take the car on a business trip for ~3 weeks. I drive a total of 1000 miles before my CEL comes on, on my way back home. 400 miles straight ride down, 400 miles straight ride back, daily driving adding up to ~200 miles. It read the code above. I was going to get it inspected the following day but fat chance of it passing now.

I have a 96 Sentra GXE.

I know some driving is required for the ECM to run all its tests. Would it take ~1000 miles to accomplish this efficiency test? Or was it good, then something caused it to fail. Just wondering if the CAT I put in or 02 sensor never worked or it did and something happened.

I bought bosch parts. Except for my O2 sensor which was...W...something.

I did notice that my exhaust smells a bit rich. Can a tune up adjust this? I didn't adjust anything in the engine, just replaced the exhaust. How can I test the O2 sensor? The cat converter, without having a new one put in?

Could the "richness" have coated up the converter and sensor throwing off the readings? Can I clean it?

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Old 09-30-2010, 04:44 AM
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So, you had a new exhaust put on. Are you sure the exhaust system was the proper one for your car?

Replaced the converter. Was it an aftermarket (welding and clamps required) or was it an OE direct fit?

Replaced the O2 sensor. Was it a universal one (had to wire it in) or was it a direct fit?

I am not sure how many CATs a 96 sentra has. I know my 2000 sentra has 2 of them. One that connects to the exhaust manifold and then one under the car. In my car, bank 1 means the one up near the manifold or so I am told.

These things are kind of hard to diagnose because:

P0420 is set after the computer has performed an efficiency test on the catalytic converter and was found to be below a certain threshold.
This doesn’t necessarily mean that the converter has gone bad. There are a number of things that can cause this code. Some, not having anything to do with the converter.

Vacuum leaks, plugged injectors, leaking injectors, one more O2 sensors, misfiring spark plug(s), ignition or valve timing, a leak in your exhaust system and the list goes on and on.

Please reply back with responses to the questions put forth and we will try to get this sorted for you. Any additional information you can give could prove to be helpful too.

As far as the inspection, you can do what a lot of people do. Go buy a little 40-60 dollar code reader and clear the codes to reset the SES light in the parking lot before you go in to have the vehicle inspected. The SES light should not come on before the tests have been completed..Not saying don't get the problem fixed, just a possible workaround incase the time comes and it is not fixed.
2000 Sentra GXE 1.8L 4cyl

It's all fun and games until someone loses an eye...Then, it's just fun you can't see...

Last edited by nobardin; 09-30-2010 at 04:48 AM.
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Old 09-30-2010, 04:54 PM
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These were all aftermarket OE direct fit parts. No welding required. Sensor was direct fit as well, aftermarket. The one I replaced is the converter on the bottom of my car along with the rear O2 sensor.

Sometimes the engine can seem louder than usual. I did the repair with a mechanic friend of mine. We checked around the pipe for any potential gaps where it could vibe against the underside. He said it was because the exhaust was all sealed up so the air is pushing through. I reset the codes and have driven ~100 miles. Some tests haven't completed but I can get away in PA with 2 unfinished monitrs, so I told by the internet.

I do have issues staying connected to my ECM via OBDII, I get disconnected as it tries to download misc codes. But I think I only had that one code. Like I said, sometimes it can smell gassy but I guess that is the definition of this error code.

Given the open endedness of this I might just be best off letting a shop take care of it if it comes back
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bank, catalyst, efficiency, p0420, system, threshold

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