2020 l5p duramax knock at idle cold, worse hot

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
21,065
4,735
113
Phoenix Az
The only stuff im finding is from the early trucks before all the ECM updates that helped fixed that for the injector and timing knock. They've gone through quite a few revisions since 17 from what i found.

as for tsb's, i honestly dont see any for a 2020 for "thumping". the only ones i found similar are the ones in the purple that i clicked on. they just state about misfire codes and how to diag or the other is about the DEF tick i already stated and possibly the decel rattle but the decel rattle will only occur once during a key cycle (if you even hear it) per the fuction GM has programmed into the ecm so the injector timing for each individual injector is set. if the rattle continues after one cycle and no key cycles between, its not the active decel injector timing. as ive said, ive never heard it till the DPF died and the others ive driven or rode in have not done it. are there some out there that make noise? most likely. do they have the most up to date ecm software? how many miles are on them now? are they running any kind of tuning? how healthy is the fuel system? are there any other systems that are not happy attributing to the tick or rattle being heard? all variables but im not saying it cant happen. at the end of the day, these are still miles quieter than a LBZ. the fact the dpf made the injectors so sensitive on my truck shows how everything needs to play nice. you cant run these trucks into the ground, goes for all ford, dodge, and others.

2020 tsb's.png2020 tsb's 2.png2020 tsb's 3.png2020 tsb's 4.png2020 tsb's 5.png
 

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
21,065
4,735
113
Phoenix Az
Ah found it, its PIP5711. its a prelim info, not a TSB.

whole list of those but thats no different for any other year dmax.
 
Last edited:

Tonyg

New member
Apr 3, 2020
1
0
1
Banks Power has no knowledge of the "thumping knock" sound on the 2020 L5P Duramax. It sounds like a bad crankshaft main bearing.
 

Hoser

Active member
Jun 19, 2016
226
28
28
Farmington, MN
Not sure how I missed all these Posts.

The document that 2004LB7 posted is what I’m talking about. It’s well known, I’ve read about the issue in many threads just doing a google search. Even guys that I know with a 2020 are saying they hate the thumping at idle.

Tonyg - how do you know that Banks has no knowledge of the thump? Regardless of whether they know about it or not, it’s a real issue. I’ve got videos of all sorts of irritating noises that aren’t on any TSB list.

Oh, and my decal rattle/knock happens all the time, and it’s loud.

I‘m glad yours is quiet, but mine is not. All in all, this 2020 is the most disappointing and problematic truck I’ve bought.
 

Mike L.

Got Sheep?
Staff member
Vendor/Sponsor
Aug 12, 2006
15,686
232
63
Fullerton CA
LML's had the same complaints years ago including mine. Noise went away on just about all of them.
 

NC-smokinlmm

<<<Future tuna killer
May 29, 2011
5,013
223
63
At Da Beach
The lml is the most refined Duramax to date. You went from the last gen 6.6 to the new design, like the lb7 it s going to take time to refine it. That is why I held onto my 16 LML and will untill 2022 when the new updates for engine/power train and interior are implemented. I hate your dissatisfied but it's a new power plant and it will take time to hone it in so to speak...
 

Hoser

Active member
Jun 19, 2016
226
28
28
Farmington, MN
The lml is the most refined Duramax to date. You went from the last gen 6.6 to the new design, like the lb7 it s going to take time to refine it. That is why I held onto my 16 LML and will untill 2022 when the new updates for engine/power train and interior are implemented. I hate your dissatisfied but it's a new power plant and it will take time to hone it in so to speak...
I would’ve loved to keep my LML, but unfortunately, living in the rust belt makes that difficult. My frame was crazy rusted, rockers were starting to go, and rust was starting to bubble up over the fenders. It is funny that you mention that though, because the L5P has been out for four model years, and now with the “updated” L5P in the ’20 is when these issues start to surface.
 

NC-smokinlmm

<<<Future tuna killer
May 29, 2011
5,013
223
63
At Da Beach
When they change engine codes its considered in update, GM probally had to repackage it for new engine compartment. No major changes yet.
 

Hoser

Active member
Jun 19, 2016
226
28
28
Farmington, MN
When they change engine codes its considered in update, GM probally had to repackage it for new engine compartment. No major changes yet.

Yes, but there were several changes to the 2020 L5P, a big one is the whole new front cover and drive system for the fan, I would consider that an ”update”, along with the new oil cooler and coolant changes. Some suspect the noise is coming from the new front cover/belt drive.
 

Hoser

Active member
Jun 19, 2016
226
28
28
Farmington, MN
Yes, it is a diesel. But it has a loud thumping noise that never goes away and drives me nuts.

I’ve had several new Duramax trucks, I have them around regularly, I work on them, and have many friends with them, this does not sound normal. The only other Duramax trucks that I know of personally that sound like this are 2020 Duramax’s.