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After my last posts, I took the truck out in the country and opened it up 5 or 6 times. The CEL went away on its own and stayed away for a week. But then it came back. Chevy did 18-NA-361 under warranty, you can find it online. It relates to particulates in the fuel filter housing. They clean the housing, replace the filter and flush the fuel supply lines ( supposed to be 2-3 gallons). This one is a little scary to me. The document mentions metal in the housing from manufacture or a clogged fuel tank vent as the cause of the particulates.

Chevy said if the particulates got past the filter into the injectors or engine the codes would have been P0171 (fuel lean), P0172 (fuel rich) or the dreaded P0300 (engine misfire).

Anyways, I think they are on to something. I hooked my code reader up on the drive home. I got P026D pending (no CEL) almost immediately and cleared it. P026D pending (no CEL) came back almost immediately, I cleared it. P026D pending (no CEL) came back almost immediately, I did not clear it and drove home, about 7 miles all together. The point is, it used to take many miles before P026D pending showed, so whatever they did, maybe they did not do it enough, but it seems to have triggered the condition. I think I read somewhere it takes 17 consecutive seconds of P026D pending to get a P026D and CEL.

The struggle is real and the saga continues. I really like this truck, but part of me thinks I would have been better of keeping my 98 Dodge.
 

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Got the same one on my 18. I thought it was related to the MAF sensor BUT I loosened my fuel cap and the code remains pending with no CEL. This comes from another thread about the tank vent being plugged. Another issue I have is the electonic brake controller canbus A offline / no com and canbus b offline / no com.
Im still digging. Wish i had my LML back.
 

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That is funny. I have an aftermarket brake controller and it recently started giving the E.r code for system failure.
 

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No CEL yet. The P026D pending went away also. Maybe the fuel filter housing/fuel line flush/clean was the trick.
 

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No CEL yet. The P026D pending went away also. Maybe the fuel filter housing/fuel line flush/clean was the trick.
I have been battling the same code now for a few months. Happened when we were at a rest area halfway up GA. Got it reset, came back on 600 miles later. Reset it again, came back 20 miles later. Took it to a diesel guy, started off with a plugged up air filter--reset values on it and it went away for about 700 miles until it came back on the other day.

Dropped it off at dealer and a few hours later they are replacing all 8 injectors. They said 1 was faulty, but better off replacing them all at once.

(Under warranty, 2017 with 53k miles)
 

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On one of my initial services by Chevy for this code, they checked my injector balances and said they were OK, but maybe that is not enough of a check? I read somewhere they need to check the returns also?

After they did the fuel filter replace/housing clean/line flush (18-NA-361) the P026D went away. It has been 2 months+ and the CEL only came back once for a short while, then went away on its own. I keep checking for a P026D pending with my code reader and I do not see it.

The guys at PBP Motorsports were nice enough to answer a few questions about this for me. They thought given my truck had low average mph (~11) when I bought it, that the exhaust systems was gunked up. So, I have been taking it one the highway for the regen cycles lately. Maybe that helps too.

From all the posts/solutions, I think this is a fickle code. I hope the new injectors solve your problem Mayer!
 

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On one of my initial services by Chevy for this code, they checked my injector balances and said they were OK, but maybe that is not enough of a check? I read somewhere they need to check the returns also?

After they did the fuel filter replace/housing clean/line flush (18-NA-361) the P026D went away. It has been 2 months+ and the CEL only came back once for a short while, then went away on its own. I keep checking for a P026D pending with my code reader and I do not see it.

The guys at PBP Motorsports were nice enough to answer a few questions about this for me. They thought given my truck had low average mph (~11) when I bought it, that the exhaust systems was gunked up. So, I have been taking it one the highway for the regen cycles lately. Maybe that helps too.

From all the posts/solutions, I think this is a fickle code. I hope the new injectors solve your problem Mayer!
I've been gracious enough to talk to a few chevy technicians and there have been 2 revisions in the 2017 and 2018 original injectors. The latest (and final) coming in 2019. They need to replace all 8, then update the ECM. They will check the returns on the drive afterwards to see if there are any possibilities of the injector wires---those are also a known culprit with the code.

Lets hope! LOL, thanks!
 

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Yeah, I've been suspicious of the injector wires too. I was going to suggest that if and when it goes back in for that code.
 

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Well after many months, the P026D is back. I wonder if the 18-NA-361 (Fuel Filter/system flush) was the trick. I say that because my filter is now down to 60% life remaining.

But, on the other hand, I found this new bulletin related to that code (20-NA-197) that says the fuel pressure sensor wiring connector gets corroded and needs to be cleaned/replaced. This makes sense to me. My truck always estimates the wrong MPG on the DIC. For example, DIC always says 17.2 mpg, but direct measurement is 14.5-16.5 depending on the number of regens between fillups. 1 regen = 16.5 mpg, 2 regens = 15.5 mpg, 3 regens = 14.5 mpg. Checking the status of the connector is something I could do but I cannot find it. I found a connector on the drivers side at the top back of the engine that looks like it goes to the fuel rail, but it only has two wires, not 4 like the one pictured in the bulletin. I tried to find it in an online in a parts diagram, but have not figured it out yet.

Can anyone help me locate the fuel pressure sensor wire connector on a 2017 L5P?

Thanks-
 

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Fuel pressure sensor is above the spare tire on the passenger side. I have had to replace mine.
 

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Manifold inlet temp sensor and the scanner says its permanent.
'Permanent' in this case means that the truck will clear the codes when it is satisfied that the problem is resolved. It may take 50 restarts (some number or other condition) and the ECM will clear the code.

Also see P026D accidental discovery
 

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At the risk of beating a dead horse-
I've found that the P026D can relate to one of many potential problem causes. I've seen numerous posts regarding a filthy MAP sensor, where an outright replacement did nothing to eliminate this error. MAF sensor was also mentioned in several places and I even replaced mine- no permanent change. Another referenced an air intake problem where the airflow to the intake manifold was low (suggesting a loose connection somewhere between the air cleaner box and the intake or, a clogged filter). I've had both NOx sensors replaced (expensive "fix", w/o any problem resolution).

I noted that one day while refilling my DEF, I had slipped and somehow managed to make contact with the harness connector at the MAF sensor. I thought i saw a piece fall off, but couldn't confirm; however, from that point, I noted that the connector shell (harness side) was sitting at roughly a 30 deg angle to the sensor- not "in line" with it. The wiring harness was "tight" IMO. I removed the harness mounting tabs (at the air cleaner box) and pulled up on the harness, relieving the strain at the connector, then ty-wrapped it into place at other points. After clearing the codes, I had in excess of 260 "warm-ups w/o an emissions malfunction" (WwoEM is what I think shows on my Edge CTS monitor). A good jarring from a pothole will rattle the harness enough to create a momentary break in the MAF sensor's connection and the code returns. I'll clear the code and we continue on.

Bottom line is that my problems may still be hidden and given the complexity of these emissions systems, it may never fully be resolved. If there was a "hard failure" of a sensor, I'd expect this DTC to consistently repeat itself. But it doesn't. To eliminate one variable, I'm considering taking the truck to the dealer and having them replace the connector shell at the MAF sensor as it still appears "very loose". As an aside, just remember that when you clear the error codes you also reset all of your emissions ready flags- which can take several hundred miles to reset on their own. This will be important if you are up against an emissions check as required by your state's DOT.
 

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Having a scope (oscilloscope) is almost a necessity these days. Without a scope, it is extremely difficult to tell if your GMLAN is correctly functioning, and if it is NOT functioning correctly, your truck is going to have problems, often times very erratically. And if you can confirm with your scope that the GMLAN IS functioning correctly all the time, you can begin to focus on other symptoms and the problem you actually need to solve. A scope, hand in hand with a wiring diagram, can lead you either to the solution or rule out false/impossible leads.
 

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At the risk of beating a dead horse-
I've found that the P026D can relate to one of many potential problem causes. I've seen numerous posts regarding a filthy MAP sensor, where an outright replacement did nothing to eliminate this error. MAF sensor was also mentioned in several places and I even replaced mine- no permanent change. Another referenced an air intake problem where the airflow to the intake manifold was low (suggesting a loose connection somewhere between the air cleaner box and the intake or, a clogged filter). I've had both NOx sensors replaced (expensive "fix", w/o any problem resolution).

I noted that one day while refilling my DEF, I had slipped and somehow managed to make contact with the harness connector at the MAF sensor. I thought i saw a piece fall off, but couldn't confirm; however, from that point, I noted that the connector shell (harness side) was sitting at roughly a 30 deg angle to the sensor- not "in line" with it. The wiring harness was "tight" IMO. I removed the harness mounting tabs (at the air cleaner box) and pulled up on the harness, relieving the strain at the connector, then ty-wrapped it into place at other points. After clearing the codes, I had in excess of 260 "warm-ups w/o an emissions malfunction" (WwoEM is what I think shows on my Edge CTS monitor). A good jarring from a pothole will rattle the harness enough to create a momentary break in the MAF sensor's connection and the code returns. I'll clear the code and we continue on.

Bottom line is that my problems may still be hidden and given the complexity of these emissions systems, it may never fully be resolved. If there was a "hard failure" of a sensor, I'd expect this DTC to consistently repeat itself. But it doesn't. To eliminate one variable, I'm considering taking the truck to the dealer and having them replace the connector shell at the MAF sensor as it still appears "very loose". As an aside, just remember that when you clear the error codes you also reset all of your emissions ready flags- which can take several hundred miles to reset on their own. This will be important if you are up against an emissions check as required by your state's DOT.
A reset is not a biggie in my world. Truck won't regen with CEL on and my scanner can force a regen if needed.
I'm personally tired of fighting city hall myself. This past weekend I went chasing after the fuel rail pressure sensor connector ( TSB for P026D ) which requires removal of the cold CAC line and I found oil in the CAC. The cold boot was wet with oil and the temp sensor had oil on it. This is not a good thing especially at 80k.

Im in touch with the dealer and if he thumbs down the oil in the CAC this pig will get a full coat of lipstick and we will see her later.

JMO
 

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My truck will regen with a CEL on (P249D). But I don't know about the P026D.
 

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A reset is not a biggie in my world. Truck won't regen with CEL on and my scanner can force a regen if needed.
I'm personally tired of fighting city hall myself. This past weekend I went chasing after the fuel rail pressure sensor connector ( TSB for P026D ) which requires removal of the cold CAC line and I found oil in the CAC. The cold boot was wet with oil and the temp sensor had oil on it. This is not a good thing especially at 80k.

Im in touch with the dealer and if he thumbs down the oil in the CAC this pig will get a full coat of lipstick and we will see her later.

JMO
We're you able to get the CAC off to get to the sensor and inspect it?
 

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Yes and no. When I pulled CAC cool side I found oil so I stopped there. This meant there was oil all through the cooler and at the time i did not know this was normal. I wanted to preserve the evidence for a dealer examination.

Right now I'm in the que for a dealer appointment. Later research tells me this is normal however and likely the dealer will say same and boot me out under the 5/100 drivetrain warranty.
 

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I've got the same bane of a code on my 2018 GMC L5P with it starting this spring at around 60K miles. The dealership flashed the computer, loaded a new program and sent me on my unhappy way. It returned within a week so I brought it back in and they replaced the MAF sensor. That lasted about 3 weeks.....I had the code deleted this week and are waiting it to return now, especially after reading your posts.
My question at this point is it worth hanging onto to this truck and what harm will be done running with that code?

I bought an extended warranty with it and there doesn't seem to be a real clear answer as to a fix. The dealership seems to be clueless and because I've changed my fuel filters in the past (earlier than regularly scheduled) they've hinted that warranty will not be covered.
I'm disgusted and at a loss as to what to do now.
 

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I've got the same bane of a code on my 2018 GMC L5P with it starting this spring at around 60K miles. The dealership flashed the computer, loaded a new program and sent me on my unhappy way. It returned within a week so I brought it back in and they replaced the MAF sensor. That lasted about 3 weeks.....I had the code deleted this week and are waiting it to return now, especially after reading your posts.
My question at this point is it worth hanging onto to this truck and what harm will be done running with that code?

I bought an extended warranty with it and there doesn't seem to be a real clear answer as to a fix. The dealership seems to be clueless and because I've changed my fuel filters in the past (earlier than regularly scheduled) they've hinted that warranty will not be covered.
I'm disgusted and at a loss as to what to do now.
Im with ya bud, 18 GMC with constant CEL and now the dreaded P289 code which is DEF quality, or a NOX sensor or some other unknown. Ive read where dealers throw a NOX sensor at it and nah, thats not it so...they don't know. I threw in 5 gals of Blue Def thinking maybe it would help out. Had an issue like this at 10k miles. I left the truck at the airport and it was 70 degrees, I came back to 43 and rain. 10 miles from the airport the dash lit up like a Christmas tree and DIC went into bitch mode. I stopped and threw in 2.5 gals of DEF and DIC shut up but still had a CEL. Cleared that and rest of the trip was good.

I'm at 80k with no warranty other than 5/100 and a CAC with oil in it plus the CEL. In the South there is a two week back log for a GM diesel tech AND CHEVROLET CANT WORK ON MY GMC UNDER WARRANTY. Thank you GM. All being said I think its time for her to go. Prices are outrageous and I'm still under 100k. Carvana offered 45k and I think I can get 50 odd on the street.

I share your disappointment.....
 
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