I bought a 2001 gle and the p0420 popped up almost immediately. After looking for all the suspects (injector, exhaust leak, etc) and cleaning the throttle body, jiggling 02 sensor connections and a week of clearing the code time after time I somehow stumbled on the answer - now no code after 300 miles and counting.

Here's what I did:
1. Finally was able to pull apart the bank 1 sensor connection, blew it out and re-connected it.
2. Poured a bottle of Chevron techron into the tank and filled up with 89.
3. Topped up the oil, which was at the low end of the stick.

I guess it could have been a bad harness connection or a clogged injector dumping raw fuel into the exhaust or perhaps fumes from low oil.

Any conjectures from anyone?

 

y u running 89?

 

please to make the car retarded...run high-test please

 

ive had the P0420 for about a year....

please use the correct gas

 

I ran 89 because 91-93 burns slower and if it was the injectors I wanted to eliminate unburnt fuel.

Like the title says maybe it was all voodoo.

Back to 91 and we'll see what happens.

 

 

nissan cant even figure it out so i gave up

many things can cause it. when i clear it, it takes 2-3 weeks to come back so clearly it isnt a real constant problem

 

Thats not the gas cap code is it?

 

no

 

they can but it just costs money and perhaps having to replace more than 1 thing till they get to the problem and having some comebacks (bad for the technician) But if you have patience and able to keep spending money till they fix it and have a good tech working on your car they should be able to fix anything
Sometimes it's not 100% straightforward as it sounds.

 

I had the P0420. I had the dealer reflash the ECU, that didn't work. I replaced the O2 sensor and that didn't work. I replaced the front pre-cat and that DID work.

It is one of those three things. I was lucky to find a used front pre-cat for cheap. New they go for around $400.

 

My 2001 GXE threw a 0420 code. The shop that checked the codes for me for free said they did not clear it, and they didn't, light stayed on. It ended up parked a lot over the next ten days or so, as I was out of town two different times. I don't remember now when I noticed that the light went off -- it might have been when I started it at the airport, or shortly thereafter. Took it to regular mechanic to get it checked out so it would pass emissions (obviously it failed with the light on, but it bought me time to get it fixed without late fees). When I mentioned the light had gone off, the thought was there was some sort of intermittent problem. They called me after checking everything out and said they thought they could "get it to pass". When I picked up the car (after also getting the A/C fixed). I looked at the paperwork at home, and in their narrative it says that there were NO CODES STORED, and computer was running fine. Does a code just disappear like that, and if so, what does THAT mean?

 

P0455 is the gas cap.

AZMaxima53-if the computer doesn't detect another fault over a certain amount of restarts and drives, it turns the code off.

 

it's not 91-93 burning slower. it's actually 89 buring quicker, quicker before the sparkplugs ignite it witch cause the engine knock.

 

We've had the eternal 0420 CEL practically since we bought our '01 SE new. We've tried the ECU flash. That worked for about a week. Then the code came back. Eventually, the dealer wanted to replace the main cat, even though they were positive it wasn't bad. Of course, the car was out of warranty by then (we put major miles on our cars...we burned-through the warranty in just over a year)

The car still runs as well as ever. We just leave it. Occasionally, we have the codes pulled to make sure we aren't getting any other problems. So far, so good. We just have this eternal CEL.

 

+1. I just fuggettaboutit. SES light makes me happy

 

sighhhh.. i too got the P0420 code.. bought my car to nissan, they told me that the precat on bank one is bad... after getting a quote of $1300, i proceeded to read every post on here about p0420... thought about doing the warpspeed ypipe.. thought about doing a sparkplug nonfouler fix.. i just decided that i'll order a eastern Catalytic precat online..for $298 and install it myself.. since it's all bolt on's... get it fixed once and for all... i can't see myself dinking with it.. especially if nissan themselves told me my precat is bad... wish me luck.. off to walmart to buy a bottle jack so i could put my car on stands...

 

I brought my Maxima to Nissan because of the P0420 also. I was hoping the reflash would fix it, but they insisted I pay the diagnosic test. After an hour of wait, they told me it was my WarpSpeed y-pipe because it has no pre-cats (which I obviously knew and have the pipe for 1yr no problem). They quoted me $1400 for the oem y-pipe + guarantee fix for P0420. I left of course because I still have my oem y-pipe. I was due for smog check and of course it would be instant fail with CEL on. I reset the car, got on the freeway right away, drove for 50miles straight at 70mph to get my cat ready, and went to smog station. I passed 15mph run with no problem, but failed 25mph by one point. I redlined every stop, revved the crap out of the car, drove a few minutes more, got back to the station and started revving it until it was my turn, and barely passed 25mph run by one point. 80miles since reset and P0420 still not triggered. Knock on wood.