EJCarter

Just FYI if there is interest... CCM sells just the diff drop spacers too. They will fit 2011-present 2500/3500 trucks. Works with all brands of leveling or lift kits. It comes with (4) spacers, (4) longer bolts, and washers. $45.00. There are quite a few good reviews where adding these spacers eliminated the vibration. www.ccmoffroad.com

You might try contacting Phil Gamboa...www.harnessdr.com...he is the guru for GM electrical / mods.

Did the Cognito kit come with diff drop spacers? If not, I would add these. It will lower the diff a little which will decrease your CV angle... Pic is one of my rear spacers...

I had the same P21DD code come up about three months ago. My dealer ran the check and the DEF heater / pump assembly would need to be replaced...but it was on a nationwide back order. They cleared the code and let me know they would call when the part came in (they had 10 on order as a couple other trucks had the same code and needed the same part, plus they wanted some in stock). Approx a month later, they received a few heater / pump assemblies and replaced mine. During that month wait, my check engine light did come back on a few times. I asked the dealer about the truck going into limp mode. They said there is a chance, but it should be a rare occasion from this issue. I wasn't too confident in their answer. They also stated, like Hillwood stated above, it will come up on the DIC and give you a number of miles before going limp...I think they said like a 50 mile "warning." The dealer also knows I have a CTS2 monitor that will run and clear codes. They said to clear it if it returns. This will keep from driving it too long with an active code (CEL), thus reducing the chance of it going into limp mode. I never had any limp issues, limp warnings, etc...and my CEL was off when I took it in for replacement. Since it's been replaced, no further CELs have come up... I would confirm your closest dealer has the part in stock. If so, see if they can put one aside for you so you don't waste a trip. If they don't have any in stock, see if they can order some now... It should only take about an hour or two to replace if they have a good diesel mechanic. I wouldn't worry too much about the limp mode. It sounds like you were able to read your code ? If that's the only code you are seeing, I'd clear it. If it comes up again, confirm it's the same P21DD and clear it again... And yes, this part is covered under warranty. GM is having so many problems with our DEF / emission system, they extended the warranty on it. I believe I heard it was 10 years /125K miles...but double check that...

Yes, mine is a '16...same as yours, so you will have no issues...

Yes, but I can only confirm Diode #2 is for the "LED lights in the mirror to come on in reverse", as I have done this mod to my truck. It has worked with no issues for the last couple years. You may just want to confirm if the pin numbers (diode locations) are the same for your 2019. I wouldn't think it would change from 2016, but you never know??? I personally can't confirm Diode #1 "fogs with parking lamps" as I have not done this mod to my truck. I was only assuming it was based on a previous post within this thread...

Diodes to use are Radio Shack (part number 1N4004)...when I picked up mine, they had a 2-Pack for about $2.00. For the LED lights in the mirrors to come on when in reverse, jump from the top upper brown BCM pin to the top second from left pin of the "pink" BCM. The gray stripe on the diode must be on the "pink" side (when I say top, I am referring to the pics above as I can't recall pin numbers). I have done this and mine matches the pics... The "fogs with parking lamps" jumper must be within the brown BCM. From the pic above, the diode appears to be placed within this BCM only. I'm not familiar with this as I don't have this set up...

Have you tried to re-sync (reset) them? ...like if one is manually pushed in and now they are out of sync. Don't know if this will help with your problem, but it's always worth a try before replacing a motor... The reset process seemed relatively...but I can't remember if I saw it on this forum or the Duramax Forum? Or, possibly it's in the owners manual?

MiamiSilverado...here's another idea. Purchase that bumper with the parking sensors and remove them...fill the holes with small round flush mount LED lights with a switch in the cab... Add your fogs you purchased and now you have even more light on the front end...

Rigid Insight Back Up Light Kit 20641 If you Google this, multiple vendors sell these for about $125.00. I purchased mine through AutoAnything.com...the were 25% off at the time...

No, it does not was out the camera...the lights are actually angled down slightly as the back of the plastic step angles down a little. I don't know if this aids in not washing out the camera.

I recently installed these Rigid Back Up Lights in the bumper step. Very clean look. Light output is awesome from these very small lights. The install was fairly easy. I made a template using the light itself and taped it to the plastic to locate my holes for drilling. You need to position the light a little more on the outboard side of the step or the back of the light housing and / or wire will contact the truck body. Probably the hardest part was installing the top nut on the backside. After numerous tries, I was able to get it started holding it from the top with a long set of angled pliers placed through the opening between the bumper and body. Positive wires are connected to each factory backup light via a T-Tap, wrapped in electrical tape and the wire is protected in split loom. For the ground wire, I crimped on a ring and attached it to the bumper. There is a small screw conveniently located on each bottom corner. I am very satisfied with these lights. You barely notice they are in there...

Never had a leak...and I use the rear-tilt feature whenever it's not raining or too cold. Truck is parked outside daily and we definitely have had an increase of rain this past winter in California.