'01 Sentra GXE - SES P0420 Code - Nissan Forum
QG18 1.8L Engine Engine Discussion: 2000+ Sentra XE, GXE, & 1.8

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#1 Old Mar 26th, 2007, 06:08 PM
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'01 Sentra GXE - SES P0420 Code

Hello everyone!
I'm posting this for a friend of mine.
Her car is a 2001 Sentra GXE, Automatic. It has abour 110,000 miles on it.

About 3 or 4 months ago, the SES light came on. The symptoms (which appeared slightly before or after the light came on, I cant remember), were the car loosing power suddenly as it was riding, sometimes shaking.
A check with a local mechanic said it (the code) had something to do with the O2 Sensor, but he couldnt know for sure, so she should take it to the dealership.
The dealership said the O2 Sensor was bad, and it would cost about $900 to replace it.
We contacted the first mechanic who was a long time family mechanic and was friendly, and he said he would do the job for about half the price.
We said goodbye to the stealership and got in the car... the SES light was off, and the car drove just fine. Hmmm...
A week later, the light was on again, and symptoms returned, but not as bad as they were the first time around.
The local mechanic replaced the O2 sensor, the SES light was off again, and the car drove fine other than one difference. There was now a very noticable and strange "electric motor humm", sort of like what a remote control car makes when the car was running, and esspecialy in acceleration.
Since the car drove fine, my friend left well enough alone for a couple of months.
Recently, the SES light has come back on, but the car drives fine (the "RC Car" sound is still there).
Today, I scanned the car with my new ScanGuage2.
The code was P0420.
My research online found that it means "catalyst system efficiency below threshold".
Is this correct?
What could be the problem? could this be related to the previous problems with the car, or just a coincidense?
Also, does anyone know of a trustworthy Nissan mechanic in the Reading, PA or Atlantic City, NJ areas?
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#2 Old Mar 29th, 2007, 03:06 AM
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Location: Philadelphia
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either the secondary o2 sensor (after the cat) is going/went bad or there could be a problem with the catalytic converter itself...take it to a meineke or an exhaust shop and have them take a look at the cat, or replace the o2 sensor..btw please dont tell me you spent $450 for a shop to replace an o2 sensor for you. if you need to replace the second one ill tell you how to do it for free, because thats an absolutely OBSCENE ripoff. you can get brand new bosch o2 sensors online for like 60 bucks, and they plug right into the old harness. all you need to do is click it in, and screw the new one into the pipe with the proper wrench, nothing that should cost ANYWHERE near $900 or $450 :/

2003 GXE:Weapon-R Secret Weapon Intake, OBX Headers, B&M Ripper SS, HKS Sport Exhaust

Coming Soon:ES MMi's, Megan FSTB, Tarmaq RTB, Unorthodox Racing UDP, APEXi SAFC2, then chill and save for turbo or SR20 swap ;)
#3 Old Mar 29th, 2007, 05:26 AM
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I dont remember off hand, and I dont have my friend around to tell me, but its possible it was the MAF Sensor that was replaced and not any of the O2 sensors.
Would the replacement of of a MAF Sensor seem more like a $450 job?

In any case, I would love to learn how to change the O2 sensors.
Please, if you can e-mail me with instructions and even pictures if possible, that would be great!
my e-mail is silnthowl@yahoo.com

#4 Old Mar 29th, 2007, 05:53 PM
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Mass Air Flow Sensor 2000 Nissan Sentra - Parts - Compare Prices, Reviews and Buy at NexTag - Price - Review

thats the only site i pulled up for a new MAF ($150) but there were many more, and even to replace this its something you can easily do yourself. its also something that should only take about 20-30 minutes, maybe even less, its a matter of unplugging a harness, unscrewing clamps, putting the new one in place, screwing it in, clicking the harness on. simple straightforward job. post on here before you go to dealerships or others to get stuff like this done, itll save you alot of money as there are alot of knowledgeable sentra owners on this site ...as far as the o2 changing just gimme a day or so to take some pictures on my car for you, or ill try to find some online. its easy to do the MAF and o2's tho

2003 GXE:Weapon-R Secret Weapon Intake, OBX Headers, B&M Ripper SS, HKS Sport Exhaust

Coming Soon:ES MMi's, Megan FSTB, Tarmaq RTB, Unorthodox Racing UDP, APEXi SAFC2, then chill and save for turbo or SR20 swap ;)
#5 Old Mar 29th, 2007, 07:06 PM
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Thank you for the information and willingness to help.

Tommorow morning I'm taking the car to a friendly, and I think trustworthy, local mechanic who will look at it free of charge and tell me what's wrong with it.

I'll still want to know how to replace those O2 sensors, and if you can get me pics for changing the MAF that would be great aswell!

Again, thank you!
#6 Old Mar 30th, 2007, 03:57 PM
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Exclamation Need Good, Knowledgable Help, Please!

So... got the car looked at.

I was dissapointed, because other than just interpreting th code (P0420) and telling me that it means I need to replaces the Catalytic Converter, the mechanic did not perform any actual checks to see if that is the real problem.
So that question still remains unanswered.

However, the wierd, electric whiering noise he said is the Alternator AND its pulley, both needing to be replaced.

As my request, he checked the timing belt. Its never been replaced, and the car is at 110K
so as far as I know its 20K over due...
With the belt he recommended replacing the water pump, the alternator belt, the A/C belt, and changing the coolant (which also probably has not been done in a long time).

He gave me prices for parts, and labor seperately:
CAT converter - $589, not from Nissan, as they wanted a lot more for it.
Gaskets - $32
Alternator - $369
Pulley - $38
Water Pump - $78.90
Timing Belt - $48.60
Alt. Belt - $28.44
A/C Belt - $21.60
Coolant - $18.50
All but the CAT converter are from Nissan.

Labor for all of this put together is $660

All together comming to a little over $1900

So...... I'm desperately asking for help. Though much of this is my friend's neglecting maintenance over the years, the fact remains she does not have a lot of money, and that's an understatement. If there's somebody out there who can guide me, step by step, on what to check in the car myself to make sure the problems are indeed real, and then where to get parts for a good price, and then how to put them in, that would be exceptionaly great! Even more so, if there's anyone with a good heart and good knowledge in the southern NJ area, or the philadelphia area, or even a little farther than that in any direction... who's willing to look at the car and diagnose it with me, I'd be eternally greatful and would compensate you for your time.

I need solid, concrete knowledge and guidance please.

Please contact me here AND at my e-mail address : silnthowl@yahoo.com (the redunduncy just to make sure I get it).
#7 Old Mar 30th, 2007, 10:54 PM
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Join Date: Aug 2006
Location: Philadelphia
Posts: 72
i live in philadelphia so as far as the o2 sensor and MAF stuff i could actually show you how to do that if youre in philly..
Nissan Sentra Catalytic Converter - Sentra 1.8L 4 Cylinder Gas | 2000 2001
theres a new catalytic converter for $148.95. its not a part that should cost you almost $600 dollars, my HKS exhaust and my OBX headers barely came to that much shipped, and they are aftermarket performance parts

2003 GXE:Weapon-R Secret Weapon Intake, OBX Headers, B&M Ripper SS, HKS Sport Exhaust

Coming Soon:ES MMi's, Megan FSTB, Tarmaq RTB, Unorthodox Racing UDP, APEXi SAFC2, then chill and save for turbo or SR20 swap ;)
#8 Old Mar 31st, 2007, 12:13 PM
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Join Date: Jul 2005
Location: PA
Posts: 80
timing should be a chain not a belt and those do not to be adjusted or replaced unless they brake or your car is misfiring.

you should have a serpitine belt not indiviual belts but id have to see the engine for myself and those arent hard to replace by yourself neither is the alternator ---thats just 3 bolts or so and the pulley comes with it when you buy a new one... unless your water pump is leaking do not replace it. just buy a 4-2-1 header unit and get rid of your front cat and put sims in place of 2 of your o2 sensors---that will save you lots of money and take away your head aches--- and get the coolant flushed it will cost about $70 total including the coolant
#9 Old Apr 5th, 2007, 07:34 AM
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Yep, the mechanic was lying! A call to Nissan verified its a chain, and not a belt, and they shouldnt need replacing.
The code (also according to Nissan) is the front CAT, which is trickier to replace (just by looking at it, in my opinion), and more expensive.
Its not urgent though, so it can wait until my friend saves up some money.

The alternator is bad though, and needs replacing. I have one, with both belts, comming in the mail, and I would love to find a set of instructions with pictures somewhere.
The step by step instructions with the exploded diagram in the service manual are not that great, and they assume some prior knowledge.

Can anyone point me in the right direction?

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