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Thread: 2017 L5P with P20EE code

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  1. #1
    Join Date
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    Default 2017 L5P with P20EE code

    2017 Silverado, L5P w/81K miles. Starting to get code P20EE which suggests a "low catalyst efficiency". I can clear the code with my Edge and drive for a certain number of miles without the code reappearing- but, it eventually returns. I've seen some owners claim the #2 NOx sensor or the DEF injector may be the culprit.

    Question: is there a problem driving this thing in the near term without major problems? I can force a "mobile regen" via my Edge, so I believe my DPF is being serviced. Maybe a flakey NOx sensor? A carboned/dirty DEF injector nozzle?

    Where on the exhaust stream are these injectors and sensors physically mounted (any pics/diagrams) available? Any thoughts or suggestions?
    Thanks!
    "Chessy56"
    So. Milwaukee, WI
    '01 2500HD, LB7, ~440K miles
    "Stock" engine. Dual fuel filtration system with Kennedy lift pump, BF Goodrich Commercial T/A Traction tires (sold to a dude from Texas- it's living a warmer life just fine down there now!).

    '17 2500HD, L5P (Happy Birthday/Merry Christmas to me!!!) Currently bone stock, 120K miles.

    "Socialism is a philosophy of failure, the creed of ignorance and
    the gospel of envy. Its inherent virtue is the equal sharing of misery."
    Winston Churchill

  2. #2
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    Arrow

    The NOx sensor and DEF are not related to the "catalyst" monitoring. They deal with NOx alone. An O2 or temp sensor, or failed Cat is more likely. The sensors can read erroneously before they actually fail enough to cause complaints. Start by removing your electronic power mods (completely, not just disabled). Diagnostics with it/them in place will have you (and the PCM) chasing wild geese.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  3. #3
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    Default

    For what it's worth, the P20EE code is no longer appearing and the check engine indicator has reset itself. I'm currently not reading any DTC codes. I recall having this failure long before I reached the first 30K miles. I had the dealer's tech look into this and there were no active codes for him to work from at that time either.

    A temp or O2 sensor was mentioned- I've forced 2 "mobile regens" now (with my Edge) and the exhaust temps came up to what I've seen before. Problem appears to be hidden again, unless the sensors are indeed flaky.

    Thanks Maverick!
    Last edited by chessy56; 03-10-2019 at 14:56. Reason: typo correction
    "Chessy56"
    So. Milwaukee, WI
    '01 2500HD, LB7, ~440K miles
    "Stock" engine. Dual fuel filtration system with Kennedy lift pump, BF Goodrich Commercial T/A Traction tires (sold to a dude from Texas- it's living a warmer life just fine down there now!).

    '17 2500HD, L5P (Happy Birthday/Merry Christmas to me!!!) Currently bone stock, 120K miles.

    "Socialism is a philosophy of failure, the creed of ignorance and
    the gospel of envy. Its inherent virtue is the equal sharing of misery."
    Winston Churchill

  4. #4
    Join Date
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    Arrow

    An off-the-cuff thought is an O2 sensor. Not necessarily failed or failing, but possibly being plugged. This has been an issue, often intermittent, since they showed up on vehicles. There's usually an underlying cause, such as a "rich" condition (as it applies to gassers), or overfueling (as it applies to Diesels with a failed charge-air system, or power mods). A completed regen may explain the disappearance, with the soot cooked out of the sensor. A sensor that's out of range, but not enough for the system to see it as a failed sensor, often causes the PCM to assume an erroneous condition. It doesn't mean that something is actually broken, only that the PCM isn't getting the data it expects. That's my best guess.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  5. #5
    Join Date
    Mar 2000
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    Default

    Quote Originally Posted by chessy56 View Post
    For what it's worth, the P20EE code is no longer appearing and the check engine indicator has reset itself. I'm currently not reading any DTC codes. I recall having this failure long before I reached the first 30K miles. I had the dealer's tech look into this and there were no active codes for him to work from at that time either.

    A temp or O2 sensor was mentioned- I've forced 2 "mobile regens" now (with my Edge) and the exhaust temps came up to what I've seen before. Problem appears to be hidden again, unless the sensors are indeed flaky.

    Thanks Maverick!
    Are you monitoring soot levels?

    Are you monitoring miles since last regen?
    Kennedy Diesel-owner
    More than just a salesman-I use and test the products that I sell on a daily basis!
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  6. #6
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    Bar Nunn, WY
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    Default

    There is a recall associated with P20EE on the 17 & early 18 L5P trucks. Have you had the recall (ECM/TCM programing) done? That code is related to an NOx issue. The programing also addressed some odd 2nd to 1st shifting issues. Also soot levels are in percentage, not grams of soot as was used on previous models.
    FYI there are no oxygen sensors on the L5P diesel.

    Jay
    2023 Tahoe 3.0l diesel
    2013 Harley Switchback
    2021 Ram 2500 6.7l (sold)
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    2021 Silverado 3.0l LM2 (sold)
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  7. #7
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    Jan 2006
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    South Milwaukee, WI
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    Default

    I am not monitoring soot levels. I'd have to check my edge, but I don't recall seeing a PID for that (is that a monitored variable that is available on a Tech II or EFI Live?). And while I do see the mobile regen occurring on occasion, I have not been paying attention to the miles in between. Probably a good idea to be doing so.

    As to the recall on the P20EE, I wasn't aware of any and logging into the MyChevy site, there's nothing listed for recalls on my '17 Silverado. However, I had been dogging the dealership on a P140B code. I was getting that code when driving in heavy rain or if my induction system ingested a bunch of snow. GM finally resolved that problem and the most recent flash supposedly covered several updates. The P20EE may have been one of the issues addressed.

    I got the P20EE a couple of times when my truck was still under warranty, but the problem was always cleared by the time my dealer tech looked at it. Until recently, I hadn't had this code in nearly 60K miles.
    Thanks guys!
    Gary
    "Chessy56"
    So. Milwaukee, WI
    '01 2500HD, LB7, ~440K miles
    "Stock" engine. Dual fuel filtration system with Kennedy lift pump, BF Goodrich Commercial T/A Traction tires (sold to a dude from Texas- it's living a warmer life just fine down there now!).

    '17 2500HD, L5P (Happy Birthday/Merry Christmas to me!!!) Currently bone stock, 120K miles.

    "Socialism is a philosophy of failure, the creed of ignorance and
    the gospel of envy. Its inherent virtue is the equal sharing of misery."
    Winston Churchill

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