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Discussion Starter · #1 ·
My 2020 has had "service 4WD" on the DIC multiple times. I took the truck to the dealer and they said they checked the levels in the front and rear diffs and they were fine. Truck still puts up "service 4WD". In the most recent DIC's the truck is in 2WD with the 2WD in orange on the dash, the first time the truck was in auto with auto in orange. This got me think this "service 4WD" is looking at both diffs. I finally put the truck up on my lift and checked the front and rear diffs. Both are about 3/8 below the fill plug hole. The owners manual from front and rear diff fluid type says see dealer. My 2013 LML took a 75w-90 synthetic with limited slip additive. How full should the Diffs be? I filled the 2013 to the bottom of the fill plug and never had an issue. What type and weight oil should be used in the front and rear diffs? Both look and feel the same clear synthetic oil. Thanks for the info.
 

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The service 4wd light has nothing to do with fluid level. It has an intermittent electrical issue that they didn't find.
My '17 had this, it turned out to be a harness that wasn't completely locked together and then caused the intermittent light. (took several visits to find)

As for the diff lube, your owners manual will list the recommended oil type and viscosity.
Slightly below fill plug is fine.
Personally mine will be changed to Amsoil 90-110 once broken in
 
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Discussion Starter · #3 ·
Thank you for the info on the light, the 2020 owners manual says contact dealer for viscosity and oil type
 

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My 2020 has had "service 4WD" on the DIC multiple times. I took the truck to the dealer and they said they checked the levels in the front and rear diffs and they were fine. Truck still puts up "service 4WD". In the most recent DIC's the truck is in 2WD with the 2WD in orange on the dash, the first time the truck was in auto with auto in orange. This got me think this "service 4WD" is looking at both diffs. I finally put the truck up on my lift and checked the front and rear diffs. Both are about 3/8 below the fill plug hole. The owners manual from front and rear diff fluid type says see dealer. My 2013 LML took a 75w-90 synthetic with limited slip additive. How full should the Diffs be? I filled the 2013 to the bottom of the fill plug and never had an issue. What type and weight oil should be used in the front and rear diffs? Both look and feel the same clear synthetic oil. Thanks for the info.
Previous gen had level specs that were below the hole.
For the rear diff used with previous gen 2500 with duramax and 3500's with either engine, the correct level was between 0.6" and 0.8" below the hole.

2020's have new diffs and axle assemblies.
May or may not have the same recommended level....

Overfill results in foaming....probably worse than a little under. Don't overfill.

Takes quite awhile for diff fluid to run back down off gearing assembly and housing.
The check should be after a long sit, not immediately after parking the vehicle.


Anyone that has service specs for the 2020 diffs, please post!

Transfer case uses DEXRON-VI Automatic Transmission Fluid.
10 speed Transmissions call for DEXRON ULV Automatic Transmission Fluid

(8-Speed Transmission DEXRON-HP Automatic Transmission Fluid)
(6-Speed Transmission DEXRON-VI Automatic Transmission Fluid)
 

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Possibly off-topic but on my recent gas truck I traded in (2012 6.0 Silverado) , I had a couple messages appear like service traction control system , service trailer brake system , might of even had the same alert you have . Anyways , I just kept driving and it would shut off on its own usually by the next day . Just my two cents

I also have friends with Silverado’s and same thing happened to them


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