2014 Sierra P0172 and P0175

aspat19 · March 15, 2018

125k miles, and throwing P0172 and P0175, if cleared they come back within a day or two. Truck has had 0 issues before this, and of course, the dealer is clueless. Thoughts?

Eddie 70 · March 16, 2018

Google says that bank 1 and bank 2 too rich.

Firewurx · May 20, 2018

Basically same conditions for mine too, 127k miles and got those codes mid March. Then 0430 mid April. I finally narrowed it down to exhaust manifold gasket leak while I was checking the plugs; specifically #8. Ordered gaskets to replace this week and a couple extra bolts.

I think I lost one which is why the leak developed. Dealer said this was a common thing. I said it shouldn’t be if you built trucks to last with good parts and if it’s that common it should be a defect covered under a recall. There’s no reason for bolt heads to be blowing off the exhaust manifold.

tbarn · May 20, 2018

7 hours ago, Firewurx said:

Basically same conditions for mine too, 127k miles and got those codes mid March. Then 0430 mid April. I finally narrowed it down to exhaust manifold gasket leak while I was checking the plugs; specifically #8. Ordered gaskets to replace this week and a couple extra bolts.

I think I lost one which is why the leak developed. Dealer said this was a common thing. I said it shouldn’t be if you built trucks to last with good parts and if it’s that common it should be a defect covered under a recall. There’s no reason for bolt heads to be blowing off the exhaust manifold.

Dealer didn't build your truck or have any input as to how it is built.

Edited May 20, 2018 by tbarn

Colossus · May 20, 2018

It's not the dealer's fault that the manufacturer screwed up.

Firewurx · July 16, 2018

Yeah, ok both of you, not what I meant by saying it that way but do you feel better for correcting me, Internet Ninja? Good job. Nothing positive to contribute to the discussion.

For anyone else’s info that has anything technical and related to the issue at hand; my engine light is back on, still 0172/0175. Changed MAF also and all 02, went away 6 weeks then reappeared then went away on its own after a day. It’ll come and go spontaneously it seems. A few times it comes back right after a full fill-up. Have live data from scan tool l can add shortly.

Edited July 16, 2018 by Firewurx

BAMA 4x4 · August 20, 2018

Any luck with fixing P0172 and P0175? I am having the same issues with my 2014 Silverado 5.3 with 128k miles. I have changed the MAF and MAP. The check engine light may stay off a day or two when cleared.

Firewurx · August 23, 2018

I’m at a loss now. It’s still been a recurring issue with mine. 137k now. Took it to a mechanic I knew. He confirmed everything I found. I changed MAF, MAP, all 4 O2 sensors, PCV, installed Moroso catch can, had exhaust manifold gaskets (small leak by #8) and donuts replaced, changed air filter and oil, changed plugs again, and I know I’m probably forgetting something. Friend mechanic said pull PCV tubes and plug intake then pull PCV inlet on engine and plug that too; then if LTFT comes back is the high pressure fuel pump. Tried this a week later and it worked. All LTFT numbers back to normal.

If I pull just PCV tubes from intake and block intake it works it’s way to normal within 20 min but then both trims start going lean (positive) so I don’t believe it’s blow-by or worn rings.

Also ran injector balance test and most of the numbers were 23-28 if that means anything to anyone. It idled at his place for 45 min and it didn’t throw the light on tho. Usually after 5 minutes idling it comes on but will go out after two trips back and forth to work and as long as I don’t idle it doesn’t come back on.

Trims while driving are perfect on STFT and constant -10 to -8 on LTFT but as soon as I let off the gas LTFT tanks at -35. In park STFT has recently started coming negative too but that was only after installing the catch can.

Just days prior to that my oil pressure started dropping to 18-20 psi at idle. Got code P06DD. Tried to pull small filter behind oil pressure sensor, no luck yet on that tho.

Took it to Chevy to have them confirm after enlightening them to all my findings. They told me it was lean and they pulled codes 0171 and 0174, I called their BS. It had a pending 0172 and 0175 when I dropped it off... said oil was fine and since I didn’t have Delco filter that was the oil problem, BS again. (I did switch a week later and got no change.) I know they didn’t let it get hot enough before they looked at it. Asked them about injectors and fuel pump again, charged another $75 + $35 for injector test on top of first $75 fee, then said injectors are the problem and suddenly agreed with me that it was rich... hmmm ok Chevy?

Before going after injectors ($1900 Chevy quote) I took to a third mechanic who pulled the same PCV test off his computer to try and I stated yes that worked, he called and talked to some Chevy guys he knew and they said not many high pres pumps go bad but oil pumps do. I don’t know of a link between oil pressure and the rich fuel trims but that pump is driven by a cam that needs proper lube.

My my dad has an 18 LT 5.3 and compared all my numbers and see no difference other than his high pres fuel pump numbers are in the 2000 psi range. Mine are 1200-1400 accelerating and when I let off my command drops by the line pressure stays high and keeps climbing for some reason. I noticed also scanner says fuel pressure from pump low side shoots to 85 psi then drops to 35 and sometimes keeps falling. After I shut off for a couple hours it bleeds all fuel pressure which makes me think it’s injectors but that doesn’t explain why that PCV plug test works? Unless it’s a combo of bad injectors, bad fuel pumps, and bad oil pump. I’ve maintained my truck exceptionally well over it’s whole life.

FYI freeze frame shows FRP CMD at like 600 psi at idle and FRP A at 590 psi maybe and FRP B was at 87 psi. So that’s always been sticking out to me as an issue.

This is all started after I ran my truck dry then fueled up back in March. I ran it down really far and right after filling and starting and driving a half mile I stopped at a store and shut it off and the engine wanted to keep running. Maybe that’s where I screwed the pooch. This has been consuming my life and this last mechanic just won’t get my truck in to really take a look at it after 3 weeks. I don’t want to go back to another dealer but this needs fixed.

Sorry so long but does anybody else who reads this all have any thoughts???? I’m sure I left out lots of details but just ask and I’ll let u know what I know/observed or if I’ve tried it.

Edited August 23, 2018 by Firewurx

BAMA 4x4 · August 23, 2018

Are your issues intermittent? My check engine light may stay off a day or two when cleared and the truck will run great. Then out of nowhere the truck will start to shift funny, the engine will rev up when braking and it starts "dieseling" and will run a second or two after the key is off. I have replaced the MAF, MAP, plugs, wires, had an oil change at the dealer, removed the throttle body and cleaned it with CRC throttle body cleaner, used a can of CRC intake valve cleaner, used a bottle of Techron complete fuel system cleaner and have ran fuel octanes from 87 to 93.

Firewurx · August 26, 2018

I can manually clear it and it’ll stay off unless I idle for more than 5 min. 300 seconds is the trigger for it to come on when it sees the rich condition. I left the last one stored in it though and it went off by itself after two trips. But like I said if I idle it’ll come back and run rough. Maybe you should try that and see if it’s only at idle for you.

I bought my scanner from Home Depot for $80. Autel 529. It’s very decent. https://www.homedepot.com/p/Autel-OBDII-Scan-Tool-with-Tech-Tips-and-Auto-VIN-AL529R/303863897

Better than my old Actron I paid $250 for years ago. It pulls up 52 or 53 PIDs.

I thought it was intermittent until I noticed the pattern of it only coming on and running rough/stumbling at idle or at a long stop light. If I keep moving and shut the truck off immediately after getting to my destination it won’t come on. Changing the MAP seemed to help it drop a few points on the LTFT but only about 5 points. Still helped a little but they’re still -28 to -29 while in closed loop at idle. Better than -35 but still an issue.

I’ve run multiple bottles of fuel system cleaner through it to no avail. It’ll downshift real hard from 3 to 2 and especially hard from 2 to 1 most of the time. I bought some seafoam intake cleaner but have yet to mess with that. I checked the Haynes manual for EGR location but haven’t seen any mention of one in the manual. Whether it’s a clogged EGR or not I dunno but I can’t find it.

I then remembered I know one of the owners of another local dealer so I made a call to him and they made a call for me to the head service advisor so I called in and explained my issue briefly to him and said I’d type up everything in detail and leave it on the seat when I drop it off. So it’s going in this week Tuesday night to be looked at Wednesday while I’m out of town.

Edited August 26, 2018 by Firewurx

BAMA 4x4 · August 28, 2018

I definitely think the issues are connected to letting the truck idle for a few minutes. My check engine light does not always come on just because I let the truck idle for a few minutes, but it is almost guaranteed to come on if I let it idle for a few minutes a couple of times during the day. The truck will run, shift and brake fine once I clear the check engine light. It is like clearing the codes "fix" the truck until I let it idle for a few minutes again. I guess the simple fix is to not let the truck idle for a few minutes, but it is way too hot in Alabama for that! I keep my inexpensive scanner in the console and clear the codes every time they come on. The codes are always P0172 and P0175. I feel that I could buy you and I both a new truck if I had a nickel for every time I have cleared the codes.

Firewurx · August 30, 2018

Ya I guess idling a couple times a day longer than a few minutes is what really gets mine too. I gotta have the rough spot too and then it’s sure to kick on. I get what you mean about the heat. It’s 90 up here in PA now and I let mine idle a bunch before dropping it off at Chevy but then it wouldn’t come on! Still had same codes stored and live scanner data still indicated -30 long term fuel trim so I gave the advisor my 4 page note on all my observations and left it in their hands. Didn’t get a call today so hopefully that means they’re really tracking it down.

If you want to diagnose this more on your own I’d recommend getting a scanner that can tell you what the truck is doing in real time. The Autel scanner I have does. I dunno if that maxiscan does or not. Aside from basic tune up if that hasn’t kicked your issue I’d find a mechanic and see if they know. Leave the freeze frame in the computer tho so don’t take it in until it comes on again. If you could read fuel trims in real time and 02 sensor data you could try that PCV procedure I detailed and see if that makes a difference.

Edited August 30, 2018 by Firewurx

Firewurx · August 30, 2018

Just picked up my truck. Sticking injectors is what they diagnosed. The sad thing is I had to tell the first dealership to even look at the injectors and their diagnosis of a vacuum leak wasn’t even close. Second dealership said no it’s not a vacuum leak. They did a direct cleaning of the injectors and said my fuel trims came back within spec but that I had no codes stored. They then realized by the time I got there the guy that cleaned the injectors cleared the codes after cuz it sets off misfires and what not apparently. I’m too scared to plug my scanner in to check and they said just drive it for now and monitor it.

It definitely has the throttle response back so I feel confident they took care of the issue. Cost was $284. This particular place/mechanic said they’ve seen the injectors go bad and varnish up a lot on early 14’s. I got to talk to him for 15 min so I feel good about the whole deal. He gave me credit on my 4 page diagnosis/trouble shooting memo I typed up for him tho. That made me feel good.

If I was you I’d go in asking for an injector cleaning and see where that leads you. Don’t clear the codes before you get there tho so they can see if there’s anything else funny going on.

Good luck sir!

Edited August 30, 2018 by Firewurx