Need some technical help on my truck.

TollKeeper

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Dec 3, 2011
8,159
Brighton, CO
Not sure what forum to put this in.. If it needs to be moved, I understand. I posted here cause there is a lot of knowledge about this problem, just not this platform.

So my wives Pontiac Aztek has been throwing a code for a O2 sensor for over a year now. This V6 only has 2, one upstream, and one downstream. The upstream is the one that keeps throwing the light.

Truck runs like a top, always starts, no extended start times. New plugs and wires as well.

I checked the LTFT and STFT, and everything checks out like it should, but thought it was maybe a lazy O2 sensor, so replaced it with another ACDelco model from Amazon. Check engine came back.

Thinking maybe it was a Chinese Amazon clone, I threw a ACDelco in from NAPA, but downstream and upstream. The light came back.

I can reset the MIL light, and all is fine, until she gets on the highway, and then in about 20-30 minutes, the light is back on.

I cant gauge whether or not its related to her fuel mileage, she doesnt drive enough.. Her average is 11-13 mpg. Truck used to get 18-23, but she also drove it A LOT more. She only drives about 1600 miles a year. Yes, one thousand six hundred miles.

There are no other MIL lights or codes, and as far as I can tell, the O2 sensor is working as it should.

Emissions is next month, and a check engine light is a automatic failure.. This wont do.

Im not sure what else to try.. A Catalytic Converter?

Help?!
 
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azswiss

Member
May 23, 2021
924
Tempe, AZ
Re; catalytic converter. Have you been able to graph the O2 sensor voltages? If so, how do they compare? If the cat is functioning properly the upstream sensor should oscillate between .2V & .9V whereas the downstream sensor should be much more stable around the .6V mark.

Oxygen-Sensors-Cat-2624139917.png
 

TollKeeper

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1st that sucks about the emissions laws in CO, in PA if you drive less that 5k a year, you're exempt.
What specific code is it throwing?
I remember looking at it, and then deleting it..

The MIL is off currently, I am hoping to make it to Friday, and will get the emissions done. If not, will report back..

I seem to remember P0130
 

TollKeeper

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Dec 3, 2011
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Brighton, CO
Re; catalytic converter. Have you been able to graph the O2 sensor voltages? If so, how do they compare? If the cat is functioning properly the upstream sensor should oscillate between .2V & .9V whereas the downstream sensor should be much more stable around the .6V mark.

View attachment 106482
I dont have that type of scanner, but I can take a video of it, and post it on youtube. I seem to remember it looked like the lower graph. Will see what I can do..
 

TollKeeper

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Brighton, CO
So here is the video.

First shot is showing the temp of the engine, should be out of closed loop
Second shot is O2 sensor downstream
Third shot is O2 sensor upstream
Fourth shot is STFT
Fifth shot is LTFT

--Video below--
 
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TollKeeper

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And just like that..
And Just Like That Blank Meme Template - Imgflip


I got moved! LOL
 

TollKeeper

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@azswiss - If you need more, just let me know. Wanted to keep it short so upload would not take forever.. Just let me know which specific graph you need.
 

Mooseman

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Dec 4, 2011
25,494
Ottawa, ON
Waddaya mean you don't have a scanner? You have the most powerful one possible, a tech 2.
 

littleblazer

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Jul 6, 2014
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Video no work lol. With an 0130 (and not being able to see the video) I'd be checking the wiring first...
 
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TollKeeper

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True I do, but the graphing on it isnt as good as my TopDon, and its no where as easy to setup as my TopDon..

Heres the original link.. I think this will work..

Another video for you. Probably ignore the last bit.. That graph got really confusing for me, and I ended it. Its supposed to be B1 STFT B1 LTFT and B2 STFT B2 LTFT

 

TollKeeper

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Try it now...
 

azswiss

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May 23, 2021
924
Tempe, AZ
@TollKeeper, got 'em. If I understand correctly, the second video is Closed Loop, right?
Assuming so, then O2S11 (upstream O2 sensor) varying between .050V & .865V) looks good. At the 0:31 mark in the second video the O2S12 (downstream) range is .100V - .870V, similar in shape & range to the upstream sensor which means the cat is not doing its job. Not sure how to interpret Long Term FT as it hits -10% (i.e. is this normal, normal-ish, or other). Seems low to me. (edit: i.e. responding to a too rich condition).
 
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TollKeeper

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Both videos I am hoping are closed loop.
 

Mooseman

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Dec 4, 2011
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Ottawa, ON
Did you confirm that the code is P0130?

Both upstream seem to be working correctly but you say in your first post that there is only one upstream? From your scans, there seems to be two. There might be just one downstream if you only have one cat but there should be two upstreams. Maybe you replaced the wrong one?
 

TollKeeper

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There is only 1 upstream and 1 downstream on the 3400 v6. The front bank goes thru a crossover to the rear bank, and its collector, where the one upstream O2 is placed, then thru the downpipe to the cat, and then to the downstream.
 

azswiss

Member
May 23, 2021
924
Tempe, AZ
Trying to understand the difference between the two graphs of O2S12 between the top & bottom videos (0:21 top & 0:31 bottom). The graph on the top video is more in line with a properly functioning cat.

Capture.JPG
 

TollKeeper

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Im not sure why it was so sharp edged on the first video. Maybe it had not fully exited out of closed loop?
 

azswiss

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May 23, 2021
924
Tempe, AZ
The lower graph indicates a non-functioning cat. Surprised it is not throwing a code like P0420 (Catalyst System Efficiency Below Threshold).
 

TollKeeper

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Brighton, CO
Did you confirm that the code is P0130?

Both upstream seem to be working correctly but you say in your first post that there is only one upstream? From your scans, there seems to be two. There might be just one downstream if you only have one cat but there should be two upstreams. Maybe you replaced the wrong one?
I cant confirm the code, as I cleared the DTC over the weekend.. I will see if I can get it to repopulate over the weekend..

For sure there is only -1- upstream and -1- downstream.

Front exhaust manifold..

Crossover...

Rear Exhaust Manifold/Collector, with EGR and O2 bung..
 

TollKeeper

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The lower graph indicates a non-functioning cat. Surprised it is not throwing a code like P0420 (Catalyst System Efficiency Below Threshold).
It may have been that code.. This old rattled brain of mine... LOL

As I said, I will try to get it to re-populate the code over the weekend, and report back on this.

Right now I am just hoping it stays off long enough to get thru the emission station Friday.
 

TollKeeper

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Good luck man!
Thanks...

I am a good Mechanic.. On mechanical bits.. I hate, with a passion, electrical shit. Even when I was working in the shop, I would always pawn that off to someone under me. I dont mind doing a bit of soldering with some dielectric grease, and heat shrink.. But my knowledge of electrical is power, ground, on, and off.. I dont get this 5v reference, and whatever else is going on.

It used to be so much easier.. at least I think!
 

Mooseman

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Dec 4, 2011
25,494
Ottawa, ON
My bad. I got confused with the terminology used by scanner to identify the sensors.

Only thing left would be to verify each wire from the sensor to the PCM. Maybe it's chafed somewhere and doesn't always short out.

Or wait for the code to come back.
 
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littleblazer

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Jul 6, 2014
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If you can... I'd also suggest a quick data log while underway during the conditions that set it. May help catch what's going on. The upstream looks normal but that doesn't mean it's not at speed...
 
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oldfoggie

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Sep 20, 2022
8
Canada
on my GMC C1500 I was getting a code for oxygen sensor, after trying many things I checked the air filter, new filter fixed it. take a look at the air filter with a light behind it,
 

TollKeeper

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So went and got both the Aztek and Envoy Emissioned today. They both passed, but I think I can see an issue with the results

First the results from the Envoy. This is a all OEM Exhaust system, from the Manifolds, to the tailpipe, including the O2 sensors. Sitting at 212k miles. I think the mileage is more accurate if I say its 370k, but nothing to confirm that. The odometer says 212k.

This is just for a reference - This is all very similar to the last 5 emissions I have done over the last 5 years. I dont see a problem here.
04 Envoy V8
HC GPM - Reading - 0.0846 - Limit - 0.8000
CO GPM - Reading - 0.4839 - Limit - 15.000
CO2 GPM - Reading - 586.6739 (No Limit indicated)
NOx GPM - Reading 0.1627 - Limit - 1.500

01 Aztek V6
HC GPM - Reading - 0.0552 - Limit - 0.8000
CO GPM - Reading - 1.6505 - Limit - 15.000 <-- this is where I see a possible problem.
CO2 GPM - Reading - 482.1792 (No Limit indicated)
NOx GPM - Reading 0.2778 - Limit - 1.500

The CO GPM indicates an issue... What that issue is I am not sure
The MIL Code is P0131 - It shows 2 codes, both are the same, one is current, one is pending.
P0131.jpg

And some more vids..

And then I reset the MIL light for this video.. I am not sure why the graphs changed..
 
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TollKeeper

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Just seeing if anyone might have an idea...
 

mrrsm

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Perhaps... (according to this linked description...) ...the problem could be Wiring Harness Related. If there are any *Nicks or Cuts* in that O2 Sensor "Short Wiring Harness" leading to the Body Harness Connector... Stray Ambient Atmospheric Air can enter along the damaged or compromised special insulation and High Temperature Wires.. .and *confuse* the Zirconium Crystal Sensor fitted deep inside of the O2 Metal Body. In the absence of any other symptoms...these are only best guesses. This article is On Topic and still very interesting, nonetheless.

 
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TollKeeper

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So bringing back a my older topic. After getting the emissions done, and resetting the MIL light for that, the light stayed off, until last week. When it threw another P0131.

If I reset the MIL, it takes anywhere from 1 week to 3 months, for it to reappear.

Still have not done anything to repair it, as I dont know where to start.

As mentioned earlier, I have already replaced the O2 sensor with new OEM, to no avail.

A friend of mine thinks I need to replace the Cat, and they are not to expensive, but I rather save that money if I can.

Any more advice?

The only way to inspect the wires at the O2 sensor going into the loom is to DROP the engine. Obviously I dont want to do that! The dash comes out half way over the engine, the wiring loom is 3/4 way up the firewall. I can see it, from about 20 inchs away. I can only reach the harness connector due to the exhaust manifold, downpipe, transmission, etc.
 

mrrsm

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Suggest checking Powers and Grounds between the Fuse Box and the Downstream O2 Sensor Harness. Also try the "Un-Plug-Plug-In" Technique to re-connect the O2 Body Harness to the Rear Oxygen Sensor. Suspect some Damage to the O2 Harness that is somewhere ahead of the O2 Sensor Special Lead.
 
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Mooseman

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Dec 4, 2011
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Ottawa, ON
P0131 is for the UPSTREAM sensor (B1S1). Cat has absolutely nothing to do with it.

Maybe check the sensor's live data and see what it's doing, cycling properly. Hope it was a good brand sensor you used. Next I'd check circuit continuities from sensor connector to the PCM and other points.

I'm thinking either the sensor failed again or it's an intermittent fault if it takes that long to keep coming back.
 
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TollKeeper

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So when the code originally appeared (like 2+ years ago), I replaced the O2 sensor with a NTK from NAPA. 2 weeks later, MIL. That time I replaced it with a ACD from Amazon. 1 day later, MIL. Thinking it was a china clone ACD, I bought a ACD from NAPA.

I am pretty sure its not the sensor..
Maybe a MAF? or injectors? or just bad gas?

This is the wives truck, and with her only putting maybe 300 miles a month on it, maybe the E-10 ethanol crap is going bad?

Other than the MIL, I have no other symptoms. No foul smelling exhaust, fuel mileage has always been horrid, idles smooth, runs smooth, has good power, etc.

I really need to find a shop like SMA here in Denver.. A good diagnostician I am not!
 

Mooseman

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mrrsm

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Even though the VOP (Video Original Poster) winds up under his Daughter's Jeep Wagon... His explanation and Hands-On Demo of How to Check the O2 Sensors is Pretty Damned GOOD for figuring out Voltage source Power Confirmation and also checking the O2 Sensors for Resistance.... starting at right 1:54 onward:

Check Out the DAMAGE (Nicks) in the Downstream O2 Sensor Heater Wires (White):



:
 
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TollKeeper

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Brighton, CO
So I took the Aztek out for a long drive, so I could catch the exact moment that the O2 sensor would throw the P0131..

And this is the picture from my live data.

As you can see, the O2 sensor just quits switching. On the second pic, I pulled over, shut down the engine for a short bit, restarted it, and it operated fine for the rest of the drive.

How in the heck does a o2 sensor just quit switching like this?

20230402_183538.jpg

20230402_165351.jpg
 

Mooseman

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Dec 4, 2011
25,494
Ottawa, ON
Wiring?
 

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