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#3302306 - 03/05/14 01:35 PM P0420 and P0131 on my 3.1
901Memphis Offline


Registered: 08/14/10
Posts: 6318
Loc: Northern Kentucky
I've had P0420 before and I clear it when it shows up every so often but today I got the P0131 which I've never got before. Any definite answer to what to replace with these known codes? This is my 2002 Buick Century.

http://www.dtcsearch.com/P0420/

http://www.dtcsearch.com/P0131/
_________________________
1999 Ford Taurus 146k (Vulcan v6) - M1 High Mileage 5w30 | Fram Ultra XG 3600
2002 Buick Century 105k - Peak 5w30 / Fram Ultra XG 3980 / Filter mag

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#3302315 - 03/05/14 01:41 PM Re: P0420 and P0131 on my 3.1 [Re: 901Memphis]
ls1mike Offline


Registered: 06/14/08
Posts: 3157
Loc: Bremerton Wa
Might be time to do your O2 sensor.
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00 Trans Am
02 Silverado 2500HD
04 Grand Prix GTP
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#3302345 - 03/05/14 02:08 PM Re: P0420 and P0131 on my 3.1 [Re: 901Memphis]
bdcardinal Offline


Registered: 06/03/05
Posts: 6678
Loc: Santa Barbara, CA
The P0131 is for the front sensor that monitors air/fuel ratio. The P0420 is for the rear sensor that monitors catalyst efficiency. Odds of them going out together are slim, but it might be worth trying based on age. I would be looking for a common fault between both sensors, either an open or short to ground in the wiring or a blown fuse.
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#3302519 - 03/05/14 05:32 PM Re: P0420 and P0131 on my 3.1 [Re: 901Memphis]
901Memphis Offline


Registered: 08/14/10
Posts: 6318
Loc: Northern Kentucky
Wonder how hard they are to get at
_________________________
1999 Ford Taurus 146k (Vulcan v6) - M1 High Mileage 5w30 | Fram Ultra XG 3600
2002 Buick Century 105k - Peak 5w30 / Fram Ultra XG 3980 / Filter mag

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#3302792 - 03/05/14 09:43 PM Re: P0420 and P0131 on my 3.1 [Re: 901Memphis]
ls1mike Offline


Registered: 06/14/08
Posts: 3157
Loc: Bremerton Wa
Not hard to change, do you get them both at the same time or are the intermittent?
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00 Trans Am
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#3302890 - 03/06/14 12:07 AM Re: P0420 and P0131 on my 3.1 [Re: 901Memphis]
901Memphis Offline


Registered: 08/14/10
Posts: 6318
Loc: Northern Kentucky
The P0420 comes back every few weeks for over a year but the other one this is the first time. I keep my OBD2 Bluetooth adapter plugged in permanently and check the P0420 before I clear it every time.

Right now it's just the P0131 but I cleared it somewhat recently so I'm going to monitor it to see if the other comes back.
_________________________
1999 Ford Taurus 146k (Vulcan v6) - M1 High Mileage 5w30 | Fram Ultra XG 3600
2002 Buick Century 105k - Peak 5w30 / Fram Ultra XG 3980 / Filter mag

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#3303130 - 03/06/14 09:02 AM Re: P0420 and P0131 on my 3.1 [Re: 901Memphis]
Vikas Offline


Registered: 07/22/05
Posts: 8317
Loc: NorthEast
Those two O2 sensors are completely independent of each other. Besides P0420 almost never has anything to do with the rear O2 sensor. If you are getting P0420, that means the rear O2 sensor IS actually working! A defective rear O2 sensor will NEVER turn on P0420.

With active P0131, your engine is not running optimally and could be spewing out more emission. Determine if the wiring or front O2 sensor is bad and correct the situation accordingly. The chances are the front O2 sensor is at its end of life, so if you want to throw a part without doing any real diagnosis, put new OEM direct fit front O2 sensor.

Since you have the OBD-II, look at the front O2 voltages/graphs. If it is not switching nicely between .1 and .8 volts, or if the switching is slow or if the range is smaller, the sensor needs to be replaced. If the voltage is stuck at 0, you may have wiring problems on the O2 sensor signal line. You have the tool; use it.

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#3303226 - 03/06/14 10:36 AM Re: P0420 and P0131 on my 3.1 [Re: 901Memphis]
901Memphis Offline


Registered: 08/14/10
Posts: 6318
Loc: Northern Kentucky
Do think look normal to everyone else too? The first shot is of me going down the interstate at 65 while the engine was still warming up a little.



Another one same thing but a couple minutes later



Here is what it looks like when I let of the throttle for a few seconds and coast.



Last one is a couple seconds of WOT at highway speed.




.
_________________________
1999 Ford Taurus 146k (Vulcan v6) - M1 High Mileage 5w30 | Fram Ultra XG 3600
2002 Buick Century 105k - Peak 5w30 / Fram Ultra XG 3980 / Filter mag

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#3303557 - 03/06/14 04:45 PM Re: P0420 and P0131 on my 3.1 [Re: 901Memphis]
Vikas Offline


Registered: 07/22/05
Posts: 8317
Loc: NorthEast
well, your front O2 is good but the catalytic converter seems somewhat suspect. Look at the 2nd picture that you posted. The rear O2 is following front O2 which indicates you have active P0420. Do you really have P0131 active? The waveforms don't support that code.

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#3303688 - 03/06/14 06:51 PM Re: P0420 and P0131 on my 3.1 [Re: 901Memphis]
Trav Offline


Registered: 11/20/06
Posts: 10252
Loc: MA, Mittelfranken.de
What codes are active now. What does the fuel trim and other data look like?
When you have an intermittent O2 code with 100K on these GM cars its good policy to swap it out anyway, they are inexpensive.

The fuel trim data under similar conditions will be helpful. Trying to figure out if something is the cause or just a symptom can be a bit of a bugger, the more data the better.
Denso cost less than $32 at Rock and work well, its easy enough to swap.
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#3303774 - 03/06/14 08:00 PM Re: P0420 and P0131 on my 3.1 [Re: 901Memphis]
ls1mike Offline


Registered: 06/14/08
Posts: 3157
Loc: Bremerton Wa
Swap them. The GM stuff is a no brainer when it comes to this.
100K? You did good young padawan. smile

I only say swap because it is intermittent and when it is intermittent on most any GM it is time to change them.
_________________________
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00 Trans Am
02 Silverado 2500HD
04 Grand Prix GTP
13 Equinox
12 Passport TT

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#3303991 - 03/06/14 11:34 PM Re: P0420 and P0131 on my 3.1 [Re: 901Memphis]
larry007 Offline


Registered: 02/07/14
Posts: 83
Loc: florida, usa
if you have access to a temperature gun shoot the cat. at inlet side. Do the same at outlet side...outlet side should be substantially higher if cat is working properly. Be sure to shoot pipe, not heat shield... Allow engine to reach full operating temp first.

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#3305131 - 03/08/14 03:53 AM Re: P0420 and P0131 on my 3.1 [Re: 901Memphis]
901Memphis Offline


Registered: 08/14/10
Posts: 6318
Loc: Northern Kentucky
I was planning on replacing both anyway, July not sure where each is yet. I think one is can access from the top side of the engine the other one i probably need ramps or a lift?

Amsoil is Denso the best choice for this application?
_________________________
1999 Ford Taurus 146k (Vulcan v6) - M1 High Mileage 5w30 | Fram Ultra XG 3600
2002 Buick Century 105k - Peak 5w30 / Fram Ultra XG 3980 / Filter mag

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#3305192 - 03/08/14 07:24 AM Re: P0420 and P0131 on my 3.1 [Re: 901Memphis]
Trav Offline


Registered: 11/20/06
Posts: 10252
Loc: MA, Mittelfranken.de
Originally Posted By: 901Memphis
I was planning on replacing both anyway, July not sure where each is yet. I think one is can access from the top side of the engine the other one i probably need ramps or a lift?

Amsoil is Denso the best choice for this application?


You may need to rotate the engine by disconnecting the dog bones and using a ratchet strap.
It is in the rear exhaust manifold behind and under the coil pack.
The rear you will need ramps, it is directly behind the Cat.

Warm the engine first to make removal easier. For the front i usually cut the wire and use a deep 7/8 socket with a long 1/2" extension, flex joint (if necessary) and breaker bar.
Denso and NTK work very well in these engines and last as long as OEM.
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