O2 sensor help, - Pontiac G8 Forum: G8 Forums - G8Board.com
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post #1 of 29 (permalink) Old 11-03-2017, 08:16 AM Thread Starter
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Question O2 sensor help,

So I have scanned my G8 due to the engine light, I got 2 codes both o2 sensors upstream and downstream. Can anyone tell me where these two are located on the engine itself?

The dealer is selling me the 02 sensors and they are $135 total for both which is a deal considering that at auto zone they are like $230 for one and $113 for the other one.


Codes:

Code 1: P0138 (O2 sensor circuit high voltage bank 1 sensor 2)

Code 2: P2271: (02 sensor signal biased/stuck rich bank 1 sensor 2)

Both of these codes keep popping up, But sometimes the one P2271 will only pop up and it wont go away until I clear it. The other code sometimes wont show either. But its safe to replace them both.
Thanks for the help!
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post #2 of 29 (permalink) Old 11-03-2017, 08:37 AM
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You have to go under the car. The first sensors are on the down pipes to the catalytic converters, and the others are on the mid pipe just behind the flange connections.

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post #3 of 29 (permalink) Old 11-03-2017, 08:51 AM Thread Starter
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You have to go under the car. The first sensors are on the down pipes to the catalytic converters, and the others are on the mid pipe just behind the flange connections.
What about the two sensors in on the engine itself? There are two of them one on the left side and the right side?
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post #4 of 29 (permalink) Old 11-03-2017, 09:04 AM
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I forget, you got a GT, right? The O2 sensors aren't on the motor. The front ones (upstream) are on the just after the manifolds upstread of the cats, and the others (downstream) are on the front of the mid-pipe. I'm not sure why you're getting such high prices from auto-zone, by the way.

Part #12569429 is around 50 (front)
Part #92068713 is around 90 (rear)

These are the ACDelco part numbers. You can find others (like Denso or Bosch) that are good for similar prices. I've had good luck getting the parts guys to sell at wholesale price... maybe it's the way I talk going in there.... There are plenty of sources online with much better pricing than you're seeing there.

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post #5 of 29 (permalink) Old 11-03-2017, 09:04 AM
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If those are the only codes you're getting, you only have 1 bad sensor. Bank 1, Sensor 2 = Driver's side, downstream sensor. You'll find that sensor about a foot after the catalytic converter.

I replaced both of mine when I put in a new mid-pipe. I got NTK sensors (part number: NTK 21062) from Amazon for $64 a piece, and they're perfect.
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post #6 of 29 (permalink) Old 11-03-2017, 09:07 AM Thread Starter
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Originally Posted by Jova007200 View Post
I forget, you got a GT, right? The O2 sensors aren't on the motor. The front ones (upstream) are on the just after the manifolds upstread of the cats, and the others (downstream) are on the front of the mid-pipe. I'm not sure why you're getting such high prices from auto-zone, by the way.

Part #12569429 is around 50 (front)
Part #92068713 is around 90 (rear)

These are the ACDelco part numbers. You can find others (like Denso or Bosch) that are good for similar prices. I've had good luck getting the parts guys to sell at wholesale price... maybe it's the way I talk going in there.... There are plenty of sources online with much better pricing than you're seeing there.
No I have the V6 I wanted something in between on gas and performance.
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post #7 of 29 (permalink) Old 11-03-2017, 09:09 AM Thread Starter
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Originally Posted by ebg8gt View Post
If those are the only codes you're getting, you only have 1 bad sensor. Bank 1, Sensor 2 = Driver's side, downstream sensor. You'll find that sensor about a foot after the catalytic converter.

I replaced both of mine when I put in a new mid-pipe. I got NTK sensors (part number: NTK 21062) from Amazon for $64 a piece, and they're perfect.
Thanks! I keep getting sometimes one code and then both, I am going to replace them both tho might as well. So its all under the car? 0.o?
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post #8 of 29 (permalink) Old 11-03-2017, 09:12 AM
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No I have the V6 I wanted something in between on gas and performance.
Whoops. Forgot you had V6.

My previous post still holds true, but you'll want NGK 25653 which is $53 on Amazon.

There were others from Bosch, ACDelco, etc. Varying prices. Just make sure you get the downstream sensor (more expensive cuz it's heated), and it has the correct plug on it. I would stay away from the "DIY pigtails".

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post #9 of 29 (permalink) Old 11-03-2017, 09:14 AM Thread Starter
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Originally Posted by ebg8gt View Post
Whoops. Forgot you had V6.

My previous post still holds true, but you'll want NGK 25653 which is $53 on Amazon.

There were others from Bosch, ACDelco, etc. Varying prices. Just make sure you get the downstream sensor (more expensive cuz it's heated), and it has the correct plug on it. I would stay away from the "DIY pigtails".
I dont know what exact brand the dealer has for me, but they bought both upstream and downstream sensors for me and both are a total cost for my to buy them off the dealer is $135 isnt bad but I don't know. I think they are Bosch
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post #10 of 29 (permalink) Old 11-03-2017, 09:19 AM
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Originally Posted by Pontiacman122 View Post
I dont know what exact brand the dealer has for me, but they bought both upstream and downstream sensors for me and both are a total cost for my to buy them off the dealer is $135 isnt bad but I don't know. I think they are Bosch
Yeah, if it's $135 for all 4, that's pretty good. You might do a little better online, but not much.

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post #11 of 29 (permalink) Old 11-03-2017, 09:21 AM Thread Starter
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Originally Posted by ebg8gt View Post
Yeah, if it's $135 for all 4, that's pretty good. You might do a little better online, but not much.
All 4? I thought I only needed two sensors? 0__0.... lol Uh They have only two one up and one down... ? The only two codes are the ones I posted so I need 4 then? Or just those two?
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post #12 of 29 (permalink) Old 11-03-2017, 09:24 AM
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Yeah, if it's $135 for all 4, that's pretty good. You might do a little better online, but not much.
Definitely true. In fact, I have found many online retail have upped their prices considerably because of the "convenience" of online shopping. Because getting off the couch and driving for 10-20 minutes is less convenient than sitting on the couch and waiting 3-5 days.

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post #13 of 29 (permalink) Old 11-03-2017, 09:26 AM
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Originally Posted by Pontiacman122 View Post
All 4? I thought I only needed two sensors? 0__0.... lol Uh They have only two one up and one down... ? The only two codes are the ones I posted so I need 4 then? Or just those two?
You did fine with your pricing.

You only have two faulty sensors on Bank 1. No need to touch Bank 2 sensors.
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post #14 of 29 (permalink) Old 11-03-2017, 09:27 AM Thread Starter
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You did fine with your pricing.

You only have two faulty sensors on Bank 1. No need to touch Bank 2 sensors.
Oh ok thanks!
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post #15 of 29 (permalink) Old 11-03-2017, 09:31 AM
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There are 4 O2 sensors on the car. 2 upstream, and 2 downstream. Up vs down just refers to before or after catalytic converters. The upstreams are responsible for actual engine management, then downstreams are really just there to make sure the cats are doing their job.

Then you have the banks: bank 1 is driver's side, Bank 2 is passenger. Judging buy your codes, your downstream sensor on the driver's side is bad. Or, the cat could be bad and the sensor is doing it's job. lol But sounds like you've already been to the dealer, and they are saying sensor is bad.

My guess is they're suggesting you replace both of the sensors on Bank 1 (driver's side).

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post #16 of 29 (permalink) Old 11-03-2017, 09:34 AM
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All 4? I thought I only needed two sensors? 0__0.... lol Uh They have only two one up and one down... ? The only two codes are the ones I posted so I need 4 then? Or just those two?
Both codes you posted are for the same sensor, you really only need one. The two downstream of the cats only monitor cat efficiency. I haven't been under a V6 but the one in question should be close behind the cat. Bank 1 is the side of the motor cylinder 1 is on.

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post #17 of 29 (permalink) Old 11-03-2017, 09:39 AM Thread Starter
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Both codes you posted are for the same sensor, you really only need one. The two downstream of the cats only monitor cat efficiency. I haven't been under a V6 but the one in question should be close behind the cat. Bank 1 is the side of the motor cylinder 1 is on.
So I only need the upstream or downstream? Wouldn't hurt to get both tho right? Cause then I will have the other one just in case?
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post #18 of 29 (permalink) Old 11-03-2017, 09:57 AM
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So I only need the upstream or downstream? Wouldn't hurt to get both tho right? Cause then I will have the other one just in case?
Correct. The codes are for the same sensor. The downstream sensor on the driver's side. The downstreams are 2-3 times the price of the upstreams, so yeah, replacing the upstream can't hurt and won't cost much.

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post #19 of 29 (permalink) Old 11-03-2017, 12:18 PM
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Correct. The codes are for the same sensor. The downstream sensor on the driver's side. The downstreams are 2-3 times the price of the upstreams, so yeah, replacing the upstream can't hurt and won't cost much.
Do both upstream ones in that case then. Also the upstream sensors are the more expensive ones. I was looking on rockauto.. AC Delco upstream - $110, downstream $67

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Last edited by mjones73; 11-03-2017 at 12:39 PM.
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post #20 of 29 (permalink) Old 11-03-2017, 12:20 PM
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So I only need the upstream or downstream? Wouldn't hurt to get both tho right? Cause then I will have the other one just in case?
The code is for the downstream sensor, if your goal is to get rid of the CEL, that would be the one you want to replace. Replacing the upsteam ones wouldn't hurt, specially if the mileage is getting up there, I'd do both upstream sensors though.

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