From O2 Sensor Code, Right to a New Code (P1174)

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
I got my new upstream O2 sensors installed. I took my first trip Friday, about 60 miles, and on the way home the engine light came back on. Now it's a totally different code. Any thoughts on what this means? Related? Coincidence?

Also the truck did seem to be driving a little weird. What it felt like was, it seemed to be running extra rough whenever it was in DOD mode. If you hit the gas, it would snap out of it and run normal. When it was running rough, it wasn't running THAT rough. Just rougher than normal. Still plenty smoother than my mom's subaru's flat-4!
 

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budwich

Member
Jun 16, 2013
2,027
kanata
I think the part that indicates that the monitoring system that set the code is VERY SENSITIVE to O2 sensors... is the key. Non OEM sensors might produce a "false" code.... which appears to be your case herein since it just showed up after you change the O2 sensor.... :smile:

Maybe that's why some people change them in pairs.... which you did. :-(
 
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l008com

Original poster
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Feb 19, 2016
886
Massachusetts
Grrr I didn't go with the AC Delcos because NTK came so highly recommended. When I ordered the two O2 sensors, I also ordered four TPMS monitors that are also not working.
And I had to pay $220 to get the O2's installed because it was impossible to get at the connectors. They had to take the front drive shaft off to get at them. And $80 to install TPMS. Another $80 to have them switched out. Ugh this round of truck repairs is not going well at all.
 
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budwich

Member
Jun 16, 2013
2,027
kanata
Well, that doesn't sound good BUT don't get too excited just yet. As the posted DTC info stated, it could be "false". As suggested in the info, monitor the misfire counts to see if there is a specific cylinder or such that is causing the issue. Perhaps that might be contributing to the problem of the "non oem" part being slightly "excited".
 
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Mooseman

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Dec 4, 2011
25,262
Ottawa, ON
I've used NTK in the past and haven't had any issues. Replacing them in pairs was also a good strategy. Maybe check the fuel trims for each bank and see if there is a marked difference between them. If there is, maybe try to swap them side to side to see if one is defective and the trims follow it.

I don't get why they had to remove the drive shaft. It was just the passenger side I had problems with. They probably worked on it from the bottom instead of the top.
 

l008com

Original poster
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Feb 19, 2016
886
Massachusetts
I tried to install them before they did and i can confirm there is essentially no way to get to them from any angle. We tried reaching behind the motor but just couldn't get your arm down far enough. Also I can't swap the sensors because i can't reach them :smile:
 

l008com

Original poster
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Feb 19, 2016
886
Massachusetts
So the light seems to be going off and on every few days. So the 'error' isn't a constant one. Not sure if that's a good thing or not.
 

l008com

Original poster
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Feb 19, 2016
886
Massachusetts
I forgot about this and I just had the idea, is it possible this is somehow related? Like if you unto the air intake a little bit, the truck will conk right out. Is this part somehow magically very important?
It's a plastic tube and while I was trying to do the sensors myself, this fell out of the engine. I don't know where from. There was so much going on and so much blind reaching. It's about 3 to 4 inches long.
 

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Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
I'm drawing a blank on it. Diameter is around 3/8"? Maybe a PCV hose?
 

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
Strange development in this problem. I went to get it repaired because it's beyond my abilities to repair and I need a sticker coming up soon.

So to recap, a few months of "O2 sensor heater" error code. I replace the proper O2 sensors. That code went away and I immediately got P1174 and the engine light.
That light was on for the last 6 months. Sometimes it would go out for a day, but usually it was on steady. I'd periodically check with the app to make sure it was the same code and not something ELSE.

I stop by my mechanic to schedule an appointment because it's time to let a pro fix it. But alas he's all booked up and going on vacation, so he sells me to come back at the end of July. This was a couple weeks ago.

The next day, the light goes out. And 2 weeks later, it has NOT come back on! After 6 months. I don't know what to make of this?? Did the truck fix itself? Its never shut off for more than a day and now its been weeks. It seems like it's not coming back. Most likely when I bring this to the mechanic, they're just going to say "come back when the light comes back" which makes sense but it just makes me very confused about this whole situation.
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
So a fuel trim balance issue could have been caused by a number of things. If I'm reading this code right, one bank's trim is off more than the other. To know what is going on, you'd have to watch your live fuel trims and see what is going on. One could be leaner or richer than the other. Could also be related to the misfire you're also experiencing. Again, live data is required to diagnose something like this.
 

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
It came back today. I guess it was just toying with me.

Regarding that missfire... I'll post this in the other thread but I wonder if ALL of this might be caused simply by me needed new plugs?
 

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
Ok I've been totally ignoring this code for a while but that orange light sure is annoying so maybe I should give it another look.

The situation is that the truck is running perfectly. No issues, no hesitation, no rough running. All the symptoms you could feel were all plug/wire issues and are gone.

The only problem is the P1174 code that keeps coming back.

So assuming I am able to get at both O2 sensor power connectors, then swapping them should switch the code to P1175 and I should know that that sensor is bad... is this correct?

Also regarding "checking the live fuel trims"... what does that mean? How do you do that?
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
So assuming I am able to get at both O2 sensor power connectors, then swapping them should switch the code to P1175 and I should know that that sensor is bad... is this correct?
That is correct however the passenger side connector is a total b!tch to get at, especially to plug it back in. It's way up behind the head. I had to go through the wheel well and unhook it from the mount on the head to get it to come out enough to get it back in with my big hoof.
 

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
The guy at the shop who did them for me told me he left them in better positions so I should be able to access them myself next time if I need to.

That said, it was such a pain in the ass, and everything does pretty strongly indicate bad sensors, AND i'm out of the warranty period, so maybe I'll just replace them. Rockauto doesn't have AC Delcos right now, anyone know the part number I need?
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
I've had good luck with NTK


For replacing them, trick I learned from my Caprice, plug it in first and let it drop down, then screw it in with some opposite direction twists of the wire.
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
Well I would try to find a way to get live data from them to see if it is an issue with them. Maybe @TJBaker57 can assist with that.
 

TJBaker57

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Aug 16, 2015
2,897
Colorado
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Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
RA has them. Part number 2133536. GM genuine.


Seems there are less and less ACDelco and more GM Genuine parts.

I would still check the fuel trims via live data to check if the ones you have are actually causing the issue.

Reading through that code's troubleshooting steps, maybe there is a vacuum leak in that bank? The intake manifold gasket is notorious for leaks so maybe that one side has a leak. A smoke test or vacuum leak test with carb cleaner could find this out quickly.
 
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azswiss

Member
May 23, 2021
861
Tempe, AZ
If you can tell me how to do this, I'd be happy to give it a shot and see how it goes.
Most basic scan tools (e.g. Actron, Innova, etc.) have the ability to read live STFT (short term) & LTFT (long term) data. Similarly, an ELM327 adapter combined with an app like Torque will enable you to look at live data.
 
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Mike of Maine

Member
Sep 6, 2023
27
Maine~
The guy at the shop who did them for me told me he left them in better positions so I should be able to access them myself next time if I need to.

Is it possible that when your mechanic moved your wires that some were pinched? Did he extend them? Posts in this link give wiring diagrams in case they were not assembled correctly, doesn't seem likely. However, as mentioned, these are sensitive and could be tripped up easily by a weak connection or if when the wires rerouted, were pulled too close and melted or otherwise damaged.


Just something to consider since it seems this brand seems ok with "the crowd".
 

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
I suppose it's possible but i tend to doubt it.

However I was under there changing my oil and i rollllled over to the O2 sensors and they totally left both connectors in a position where I can actually reach them. So I just need time and some non-freezing weather to swap them and see what happens.
 

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