2020 LM2 leaking Oil (158,000mi)

[SC4R3C120W]

Trying to get thoughts on where the leak is originating from, maybe rear seal? Seems to be coming from a weird cap behind the engine / bottom of transmission AND potentially higher above the last O2 sensor on the exhaust, below the DPF / turbo area. Truck is a 2020 with 158,000 miles on it. It was in the dealer at 103,000 for new transmission and oil pump belt (did belt early since trans was off and saved some money on labor). Oil consumption has been very minimal. I change myself every 5,000miles since I commute so much and I've never been low enough to add oil. 

Edited October 21, 2025 by SC4R3C120W

[SC4R3C120W]

some more pics near the exhaust side.

[SC4R3C120W]

[SC4R3C120W]

I also have a catch can that's been on since 103,000 and it collects maybe an ounce or two every 2-5k miles I drain it (if I use a water bottle it barely fills up the bottom round part). 

[BIGDOGx]

Looks like your oil cooler lines are leaking to me.

[redwngr]

https://gm-techlink.com/?p=14641 

 

 

Diesel Engine Rear Main Oil Seal

April 13, 2021

Some 2020-2021 Silverado, Sierra; 2021 Tahoe, Suburban, Yukon and Escalade models equipped with the 3.0L diesel engine (RPO LM2) may have an oil leak concern and DTC P06DD (Engine Oil Pressure Control Valve Performance) may be set. These conditions may occur if the rear main oil seal has moved or is severely shifted out of position in the timing chain lower cover.

If these conditions are found, replace the timing chain lower cover, which comes with a seal already installed. (Fig. 9)

 

Fig. 9

 

If the seal is tilted out of position, use a caliper and record the depth where the seal is pushed in prior to removing the rear cover. Also place an indexing mark on the seal and cover, which will be helpful to the Warranty Parts Center in case the seal falls out or moves during shipping. (Fig. 10)

 

Fig. 10

 

Record the Part Unique Number (PUN) found on the white label attached to the back of the cover.

The timing chain lower cover comes with a two-piece protector/installer. The inner piece becomes the installation tool. (Fig 11, A) The outer piece simply holds them together for shipment. Remove and discard the outer piece. (Fig. 11, B)

 

Fig. 11

 

The inner piece acts as an installation tool substitute for the EN-52466-2 seal protector and fits over the bevel on the end of the crankshaft. Be sure that the inner lip of the seal slides over the rear of the crankshaft without rolling during installation or a repeat oil leak may occur. The protector/installer (Fig. 12, shown without cover) will have a snug fit to the pilot of the crankshaft.

 

Fig. 12

 

 

 

[SC4R3C120W]

Ended up with a check engine light as well, so took to dealer. Dealer found upper rear cover seal was leaking and turbo ended up being bad. Leak was more than likely caused when they changed oil pump belt / transmission 50k miles ago, but dealer blamed it on life of truck.

 

Between needing new tires soon, new battery, and repair costs being more than value of truck, I traded it in for a 26 RST 3.0 LZ0. Wanted like for like with newer engine, they had one on lot, and I ended up with many upgrades from the last truck