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Nissan Repair/2003 xterra 4cyl, manual transmission


QUESTION: Vehicle stalled out while idling about a month ago, replaced maf sensor and got it back running. That code cleared but new one p0420 came up now. Will be checking to see if cat converter is shot, but wondering what else it could be since vehicle is still having some of the same symptoms as before maf sensor went out. Rough idle, idle occasionally drops low as if it is going to stall but then returns to normal idle rpm. Occasionally  "shudders" as I start to go (first gear) as if I'm not giving it enough gas. About 128k miles, definitely due for a full tune up too.

ANSWER: Hi Jeanne -

That code P0420 most likely could be coming out because of the erratic idle throwing off the air/fuel mixture going into the cat.

The first thing I would recommend is the tune up.

The MAF, IAC solenoid will send out a code if defective. I am assuming you do not have these codes present?

After the tune up, I would check the fuel pump pressure and volume. Fuel pump issues do not activate the check engine light, so they have to be checked independently.

Hope this helps -

---------- FOLLOW-UP ----------

QUESTION: Thank you Calvin, really appreciate your input!

Did tune up and replaced plugs, plug wires, fuel filter, gear oil and replaced alternator (separate issue). All perfect for about 25-30 miles and light came back on. Have not been able to get code checked to see if it is still the p0420 because now have strong smell of fuel when we start the car now too.

Not sure what that is from, swapping out the fuel filter was pretty basic. We will be adjusting alternator belt and re-doing the gear oil (found out we were told the wrong kind to use) this weekend. Any thoughts on what could be causing the fuel odor would be helpful if you have any.

Thanks again and Happy Holidays!


ANSWER: Hi Jeanne -

Please check the connections at the fuel filter and see if there is any leaking. Engine needs to be running.

Yes, as soon as you can get the code, LMK. That will tell us what is wrong, since the light came back on pretty quickly.

Hope this helps -

---------- FOLLOW-UP ----------

QUESTION: Checked connections to fuel filter and do not see any leaks. Swapped out to the correct gear oil and let it run and drove it a short distance. Don't smell the fuel anymore.

We were able to get the code checked and it is coming back with the same p0420 code. Also noticed water dripping from the muffler and engine still sounds a little rough. Would this point to the cat needing replaced?

Thanks again for all your help!


Hi Jeanne -

Thank you for the info.
I still suspect that the reason for that code is because the engine is running rough, probably a rich air/fuel mixture and throwing that code. There is a sensor before and after the catalytic converter. The computer monitors the 2 and if there happens to be little or not change in the mixture, it throws that code. However if the mixture is not right to begin with, then it will also display the code, which means the CAT is still OK. The CAT is very expensive, so you want to exhaust all possibilities before it is condemned.

That being said, the rough idle will have to be repaired. Have you checked for a vacuum leak?

Hope this helps -

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Calvin Iwashita


All general car repairs for all models of vehicles, except technicals (overhauls) on A/C systems and transmissions.


16 years as a car mechanic from 1974 to 1990, and still repair cars on the side.


High School and college graduate

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