P0420 - Researched to death - Chevy and GMC Duramax Diesel Forum
11-16 LML Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission, Etc.

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post #1 of 30 (permalink) Old 04-14-2019, 07:59 AM Thread Starter
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P0420 - Researched to death **Solved**

Earlier this year, 20 miles before I clicked off 120k on my truck I popped a code for the DEF heater. Dealer replaced, all was good, until last week. I drive sparingly, usually to visit family or to and from the airport. On the way back from one of those trips, I popped a code P0420 for Catalyst efficiency. I reset it, came back 40mi later. After adding a bunch of the datapoints to my HP Tuners VCM scanner I noticed my DEF Tank said I was at 100% full, which was impossible because I hadn't filled it since they did the tank heater..... I always keep a couple boxes in the garage just in case so I added 2.5 gallons to the system.... still 100% and you could hear it hitting the empty tank.
I took the my laptop with and scanned again for a road test. Once it started and got under way you could see the hydrocarbon injector duty cycle 50%, while the DEF injector cycled FAST 0-15% but shows failures for pressure tests. EGT's test and show normal temps, NOX 1 and 2 only go high when I get on it hard, but I have to keep clearing the codes for the P0420 in order for the system to go into regen. Started at 48g of soot and after about 20min it was able to get it down to around 20 while driving up and down the highway by my house but reading I should probably be burning it off a little faster than that. Which leads me to believe that the DEF injector is not functioning correctly? Dealer is going to look at the level sensor tomorrow morning since that is directly related, but wondering if I clogged the DEF injector running the system dry? Could the DOC, or other exhaust parts be damaged because of DEF not being used? Sensors I can live with and replace, but if I have to go out and get a DOC or DPF and spend 2k+....... I might as well trade this thing in. I'd delete, but I live in Texas and just last month I had to convince the inspection place that the cat that was on my TA was actually enough for the car per EPA standards. Pretty sure a visual inspection of my truck deleted will go over just as bad. Plus, even deleting it all costs over 2k so bent over both ways.

Last edited by StealthGrayDMAX; 05-24-2019 at 01:26 PM.
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post #2 of 30 (permalink) Old 04-14-2019, 08:15 AM
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Not that it helps with your problem, but Tx doesn't require fart sniffer testing for State inspections on Diesel.

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post #3 of 30 (permalink) Old 04-14-2019, 08:40 AM Thread Starter
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forgot about that. Updated. 2013 Sierra LML, completely stock. I live in the Austin area as well. I know they don't sniff, but after the fight I had to have with the inspection place for my Trans Am on longtube headers after their visual inspection... not sure I want the drama.


Last year I was in and out of there, this year they were under my car with mirrors, even gave me grief on my tires trying to say they were almost bald yet they are new tires and well within spec from the manufacturer and DOT regulations. He said they were cracking down on them, so everyone that was outside of stock was getting the full rundown. They were actually lecturing a guy with a deleted F250 when I was leaving. I'd find a more friendly shop to get it done at, but something worries me that they'll all be like this after a while.

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post #4 of 30 (permalink) Old 04-14-2019, 08:57 AM
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I'd keep the DOC and the muffler, if you altered the exhaust. DOC sweetens the smell, muff....well, I like quietness running 75-80 for hours on end....not that I'm advocating a delete.

Several years ago, the normal shop I had been swingin' by for years, were all backed up. So, I went across the street to an exclusive Inspect only shop.
Not knowing the personnel, when the guy came out to go test the brakes, I kind of jokingly said, "careful, that throttle's a bit touchy!"

Didn't like the look I got. After the stop check, he pulls into the bay for the rest of the inspect. Last thing he did was to walk down the pass side with a large Border Patrol style mirror on a stick, viewing the underside from end to end.

I asked, "what are ya lookin' for?" (exhaust is original)
Lying prick said he was checking the exhaust mounts for wear....
You can't see the rubbers' conditions with a mirror on the bottom side.
I haven't been back....hate being lied to.

On the other end of the scale, the place I happened upon out on the road, back a few months ago for an inspect.....saw it was a Diesel and never even touched the truck on their way to the PC.

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post #5 of 30 (permalink) Old 04-14-2019, 09:01 AM
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Man to be honest some of these trucks are just headaches with emissions. Once they start acting up it seems all the other parts follow suit. Try a different dealer, or a performance shop. Some are better than others with troubleshooting emission issues. I know you said you didn't want to delete but I'd find a new shop and talk to the owner. Basic delete could be done with a 60 dollar delete pipe and 6 to 800 for tuning. Even cheaper if you have access to a v2. The egr and all that can stay intact. Ran mine like that for thousands of miles with no issue. Good luck hope you get it worked out.

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post #6 of 30 (permalink) Old 04-14-2019, 09:24 AM Thread Starter
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Thanks guys. I LOVE this truck, just not the emissions systems or laws to keep it there on top of the fact that they make the replacement parts for it so damn expensive so you literally have no choice to either pay it, delete it, or sell it. If I did delete it would still have the cat, a muffler and EGR. I hate smelling like the car I just drove, which is why my TA is tuned as it is and still runs a cat.

I think I have it narrowed down to that DEF injector. Found a post here saying you can add 5V and check the spray pattern and clean it. I'll wait for the dealer to look at the tank level sensor before I pull it out for testing, but if it is clogged thankfully I can get it at Rock Auto for under $150. I just don't want to be chasing 800 bucks in sensors, injectors and parts just to find out it was the DOC and I could have just deleted. Guy in my neighborhood has a deleted F250, need to find out where he gets it inspected because it sounds like a jet airplane so it definitely doesn't pass the "sounds stock" test lol.

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post #7 of 30 (permalink) Old 04-15-2019, 08:47 AM Thread Starter
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Truck is at the dealer now. FINGERS CROSSED. Explained the situation to the service rep and once I mentioned the cat, he asked if I had P0420 as the code. Said it would be a few hours so they can drop the DEF tank and check the level sensor.

Looking at the datalogs last night and this morning, I noticed a couple things.

1 - Catalyst temp B1S2 shows 1832 even cold... no matter what. EGR 1,2,3,4 all read fine.
2 - DEF Injector has failed tests for all pressure related functions
3 - NOX sensors seem to be reading proper levels
4 - DEF Injector inhibit shows REGEN ACTIVE as the reason, but regen shows INACTIVE. I can see the HC1 dutycycle going up to 50% and the DEF injector pulses 1-30% (assuming by design) as I drive.
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post #8 of 30 (permalink) Old 04-15-2019, 08:50 AM Thread Starter
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Just as a what if, I also have their appraiser looking over the truck to have another option just in case it is a massive fix I don't want to deal with. I'm mechanically inclined, but this is my first diesel and this emissions system seems like a can of worms. Insult to injury, just got my TX registration renewal letter so I have until June to fix this.

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post #9 of 30 (permalink) Old 04-15-2019, 09:39 AM
 
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If you just have to pass a visual inspection then do the delete and hollow out your factory dpf. Tuning will eliminate the sensor issues and the need for def altogether. If you hollow your dpf yourself, the only cost would be for tuning. You could get an optimized stock ppei tune for $750

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post #10 of 30 (permalink) Old 04-15-2019, 11:02 AM Thread Starter
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Well they just called......

9th injector is bad
Cat needs to be replaced
DEF Module failed? (I can't even find this part anywhere)

Said they are waiting for GM to call back to see if the DEF tank is covered (at 122k but they did the heater assembly at 119, and it hasn't worked right since). I'm not convinced the cat needs the be replaced if the injector failed, maybe it isn't getting hot enough without the extra fuel? Sure as heck not paying 2k for a damn catalyst.

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