Need some help diagnosing a 2001 Pontiac Aztek

[TollKeeper]

So I am taking @OR VietVet 's advice and posting here..

I am not much of a electrical diagnostician, and can barely work on them correctly.

So I have a 2001 Pontiac Aztek that has been throwing a code P0131. Although this is a V6, there is only a B1S1 (Bank 1, Sensor 1. AKA Upstream) and a B1S2 (Bank 1, Sensor 2, AKA Downstream)

Being that it was all original O2's at 130k miles, I just went ahead and replaced the O2 sensor with a NTK from a local parts store. Up and Down stream

A couple weeks later, the code came back.

I again replaced the O2 sensor, with a GM OE part. Up and Down stream.

Code came back. This is when I realized that the code means low sensor voltage... But I have no idea what that means.

The O2 sensor is nearly impossible to reach as it is. The wiring is even worse.

Here are some graphs, and vids, to show that the O2 sensor is literally just dropping out. Sometimes it comes back on its own, other times it doesnt.

MIL light is on for these vids

MIL light is off for this vid, which changes the graph?

As I mentioned above... A good electrical diagnostician I am NOT!
I hate wiring with a passion!

Wish I had a good diagnostician here in Denver like SMA.

 

[strutaeng]

It couldn't tell from the loud music in the background but seems like all of those were with engine at idle, correct?

So that code means engine is running lean. You probably changed a perfectly good oxygen sensor. It happens. I did it too when I was just learning.

Strangely you don't seem to indicate you also have any lean codes? Like a P0171 or P0174?

Your fuel trims should indicate the engine is running lean. Can you post a video of your fuel trims with engine at idle, then rev it up to 1k, 2k, 3k while focused on fuel trims?

Since the data drops out randomly it almost seems like it's a wiring integrity issue. Is rust and corrosion an issue there you live? Has the vehicle ever lived in the rust belt?

 

[TollKeeper]

Nope, no rust or corrosion issues here in Colorado..

Engine is at idle, full operating temp at about 700 rpm.

Not sure I hear loud music, but a background music (didnt want a YouTube strike). Had to turn my desktop speakers up to full blast just to hear it.

No other codes other than the P0131. Which is the oddity.

Been working on this specific problem for the better part of 3 years (about 5k miles), trying different and random things. No other codes have ever presented themselves during those 3 years. If I clear the code, sometimes it will stay cleared for 1 week, other times 6 months. It will still pass emissions if I clear the code, and drive the 20 miles to the inspection station.

I only accidently found the O2 sensors dropping out. Had the scanner plugged in, and on that screen, while taking the wife and kids to a mall. Was on the interstate, looked down, and saw a flat line on the scanner. Pulled over, shut truck off, and restarted it, and it was back to the normal up and down line for a upstream O2 sensor. No code set while it was doing this.

I had one shop say it was likely a catalytic converter, than had 3 shops say it wasnt. So it did not get replaced (they arent cheap!).

6 months ago, I put on a new set of ACDelco plugs, wires and a coil that looked like it was carbon tracking. #5 was a miserable mother fudger to change. Old plug did not want to come out, new one did not want to go in. Old plugs looked normal, no white indicating lean or coolant, just a normal amount of black carbon on the thread seat and none on the electrode or strap. Plugs only had 15k miles on them (previously changed about 8 years ago).

Very recently, like 2 months ago, started getting an occasional misfire. Unsure if its related. I am pretty sure it isnt, as this truck is only driven 1500 to 2000 miles a year. And has only been moved maybe 10-20 miles in the last 2 months as a result. Likely a ethanol issue (from lack of use) at the fuel filter, fuel lines, or fuel pump. It will cause the MIL light to flash, but never sets a code, like a P0300, or anything. Have a new fuel filter to put on, but need to borrow/rent a fuel pressure test kit to rule out a fuel pressure regulator/fuel pump.

I can see about getting you a LTFT and STFT video. Will likely be a couple weeks. Buddy got evicted (with his wife and 2 kids. One is severely autistic), and am helping him move into my basement until he gets back on his feet.

 

[strutaeng]

Nope, no rust or corrosion issues here in Colorado..

Engine is at idle, full operating temp at about 700 rpm.

Not sure I hear loud music, but a background music (didnt want a YouTube strike). Had to turn my desktop speakers up to full blast just to hear it.

No other codes other than the P0131. Which is the oddity.

Been working on this specific problem for the better part of 3 years (about 5k miles), trying different and random things. No other codes have ever presented themselves during those 3 years. If I clear the code, sometimes it will stay cleared for 1 week, other times 6 months. It will still pass emissions if I clear the code, and drive the 20 miles to the inspection station.

I only accidently found the O2 sensors dropping out. Had the scanner plugged in, and on that screen, while taking the wife and kids to a mall. Was on the interstate, looked down, and saw a flat line on the scanner. Pulled over, shut truck off, and restarted it, and it was back to the normal up and down line for a upstream O2 sensor. No code set while it was doing this.

I had one shop say it was likely a catalytic converter, than had 3 shops say it wasnt. So it did not get replaced (they arent cheap!).

6 months ago, I put on a new set of ACDelco plugs, wires and a coil that looked like it was carbon tracking. #5 was a miserable mother fudger to change. Old plug did not want to come out, new one did not want to go in. Old plugs looked normal, no white indicating lean or coolant, just a normal amount of black carbon on the thread seat and none on the electrode or strap. Plugs only had 15k miles on them (previously changed about 8 years ago).

Very recently, like 2 months ago, started getting an occasional misfire. Unsure if its related. I am pretty sure it isnt, as this truck is only driven 1500 to 2000 miles a year. And has only been moved maybe 10-20 miles in the last 2 months as a result. Likely a ethanol issue (from lack of use) at the fuel filter, fuel lines, or fuel pump. It will cause the MIL light to flash, but never sets a code, like a P0300, or anything. Have a new fuel filter to put on, but need to borrow/rent a fuel pressure test kit to rule out a fuel pressure regulator/fuel pump.

I can see about getting you a LTFT and STFT video. Will likely be a couple weeks. Buddy got evicted (with his wife and 2 kids. One is severely autistic), and am helping him move into my basement until he gets back on his feet.

Oh, sorry. I didn't realize that was background music.

And sorry to hear about your troubles.

So unfortunately, these intermittent problems are such a pain to diagnose. I've learned a bit of diagnostics as a DIYer and intermittent problems like this give me nightmares. The problem is they you can't ever seem to duplicate the issue. Wiggling wires sometimes helps if you happen to be looking at the correct data graph on your scanner.

But if the issue only pops up every few weeks or months, that's a challenge.

 

[TollKeeper]

So unfortunately, these intermittent problems are such a pain to diagnose. I've learned a bit of diagnostics as a DIYer and intermittent problems like this give me nightmares. The problem is they you can't ever seem to duplicate the issue. Wiggling wires sometimes helps if you happen to be looking at the correct data graph on your scanner.

But if the issue only pops up every few weeks or months, that's a challenge.

And thats part of the problem... I am currently trying to sell the Aztek. Its hard to get top dollar when the MIL can turn on at any time. And all of my interested buyers are coming from 1000 miles away (or more).

Amazingly, this Aztek is the rarest built, with a production number of 1 of 2 in this build. And the other got totalled out 4 years ago in Connecticut.

 

[TollKeeper]

Another thing... is the issue so random and hard to reproduce because the wife drives it so little??

I am planning on daily driving it once I cant the misfire cleared out, and see if its more easy to reproduce the problem..

But again, if its wiring... Due to lack of space, and how much I hate working on wiring...

 

[OR VietVet]

Where is the ECU located? Checked all related ECU grounds?

 

[TollKeeper]

Where is the ECU located?

If I am remembering correctly, inside the air filter box.

Edit: I assume you are meaning the PCM?

 

[strutaeng]

Woah! 1 of 2 built!!! I'm curious what makes it unique?

That's more rare that the 1969 COPO "Cameros" LOL

Edit: I forgot to mention that I joke with my friends on these intermittent problems. I tell them you always need like a palm reader, a priest and a mechanic to figure it out.

Sorry, I know this doesn't help.

 

[Fless]

I'd remove and inspect the connectors on the ECU, maybe using some contact cleaner like DeOxit. If you can get a wiring diagram, see if any mid-circuit connectors exist.

FWIW the other thing I read about this code, and this is kinda out there, is that the coolant temp sensor may be faulty. It might not hurt to see if those readings track with the ambient air temp; how close are they before a cold start, and are they steady and track together?

 

[TollKeeper]

Woah! 1 of 2 built!!! I'm curious what makes it unique?

That's more rare that the 1969 COPO "Cameros" LOL

Thats actually easy to answer..

This is a GT, which were only made in 2001
This one is in Citrus Green, which you could only get if you ordered it, and only produced for 2001
This one has 4 leather bucket seats in grey, only produced for 2001
This one has HUD (heads up display)
This one has factory Pioneer amps and speakers
This one has the factory hikers package
This one has the rear removeable cargo tray
This one has the factory campers package (tent, mattress)
This one is AWD
This one has the rear air suspension
This one has the sun and sound package, with the sun package deleted
This one has leather door inlays
This one has the rear seat entertainment (allows the rear seat occupants to plug in wired headphones and listen to a alternate radio station or cd)
This one has the factory rear cargo cover (extremely rare) (a piece of fabric that ties into 6 anchors)
and a few other things...

And yes, it has the cooler too.

Edit: I have also added a few rare items from its kissing cousin Buick Rendezvous. Rear seat foot rests.

I recently took out the Buick Rendezvous Navigation unit in getting it ready to be sold. Installing it was a wiring nightmare, as the VSS wire is needed, and is not in the stereo wiring harness.

Edit2: Added to the list above

 

[strutaeng]

Oh, another thing is a wiring diagram is a must on these types of issues. I highly recommend you get the AllData subscription to download all of the wiring diagrams. I think it's like $20 for a monthly subscription. But it's really worth it even if you are selling it.

Often times multiple sensor wires are shared on circuits and that will help you pinpoint problems. A wire not making good contact such a ground is often a common problem. Worst case if you have to run a new wire from the ECU to the sensor if you determine it's the problem but can't locate the location of the fault.

 

[OR VietVet]

If I am remembering correctly, inside the air filter box.

Edit: I assume you are meaning the PCM?
View attachment 406340

Yes, PCM....I was wondering how exposed it is. Sometimes, like @Fless said, the connection can be cleaned by unplugging and plugging back in. Check any wiring that you can get your hands on, leading to it. Again, any grounds. The intermittent part of this problem sure points to something like that. The CTS is another good recommendation. It tells the PCM the engine temp.

 

[TollKeeper]

Let me throw this into the mix (it just popped into my head)

About the same time this all started happening, maybe a couple months before, I was also having a random battery light on the dash. Battery was still charging, and the battery itself was good. It was another scenario of pulling over, shutting the truck off, and restarting it, and the battery light would turn off.

I originally thought it was just the alternator, and pulled it out (a nightmare in and of itself), and had it tested. Tested good. Also had the battery tested, as you have to pull it, to pull the alternator, and it was good.

 

[OR VietVet]

While I have watched and even tested starters and alternators on the parts stores test equipment, I have never trusted them as much as testing the components on the vehicle.

 

[TollKeeper]

While I have watched and even tested starters and alternators on the parts stores test equipment, I have never trusted them as much as testing the components on the vehicle.

Did that too..

Alternator Peak amperage was well within spec of OE amperage of 125amps at 117amps sustained duration, peaking (spike) during initial power up at 155 amps.

Battery tested to 87% of its duty cycle 630amp

I have since replaced the battery, it now has a 800amp

 

[Marky Dissod]

This is starting to sound like more than one wiring issue.
It looks like the sensor usually works normally, then temporarily takes a break.
It does NOT look like it's biased to favor one direction vs another.
That looks to me like wiring ...