6.6L Duramax L5P Maintenance Schedule (Service Intervals)
| Description | Service Interval(s) | Notes/Remarks |
| Replace engine oil & oil filter | 10,000 miles or when "change engine oil" message is displayed by the oil life monitoring system | [1] |
| Replace fuel filter, drain water separator | 22,500 miles/2 years or when "change fuel filter" message is displayed | --- |
| Replace engine air filter | 45,000 miles/4 years or when "replace engine air filter" message is displayed | [2] |
| Perform engine cooling system service | 150,000 miles/5 years | [3] |
| Replace automatic transmission fluid & filters | 45,000 miles (Allison 6 speed and GM-Allison 10 speed transmissions) | [4] |
| Replace transfer case fluid | 50,000 miles | [5] |
| Replace front differential fluid | 50,000 miles | [5], [6] |
| Replace rear differential fluid | ||
| Perform multi-point inspection | At oil change intervals | [7] |
[1] Do not exceed 10,000 miles between oil changes. More frequent oil changes may be advisable if towing frequently, hauling payloads near GVWR, or idling for extended periods of time. Recommend changing engine oil every 12 months if mileage does not meet service criteria.
[2] Check air filter condition at oil change intervals and replace as necessary. Driving in dusty conditions will require more frequent air filter replacements.
[3] At minimal, drain coolant from engine cooling system and replace thermostats, upper radiator hose, lower radiator hose, and replenish with new coolant/distilled water solution. Inspect remaining hoses and overflow tank, replace as necessary. Recommend that subsequent cooling system services are performed at 50,000 mile intervals after the initial 150,000 mile service.
[4]Allison 6 speed transmission features internal and external (auxiliary) filters. GM-Allison 10 speed transmission has single external filter only.
[5] Replace transfer case and differential fluid immediately anytime these components are submerged in water; water infiltration is highly likely.
[6] No service interval provided by GM; recommend replacing front and rear differential gear oil at 50,000 mile intervals to prolong life.
[7] Multi-point inspection should include examination of ball joints, universal joints, CV joints, air filter, fuel system (leak detection), exhaust system, and vehicle brake condition. Grease applicable Zerk fittings as required.
6.6L Duramax L5P Service Parts List
| Part Description | Part Number | |
| Engine air filter | 2017 - 2019 models | ACDelco A3231C |
| 2020 - 2021 models | ACDelco A3248C | |
| Engine oil filter | 2017 - 2019 models | ACDelco PF2232 |
| 2020 - 2021 models | ACDelco PF26 | |
| Oil pan drain plug | 2017 models | GM 11569943(integrated gasket) |
| 2018 - 2021 models | GM 55577568 (gasket sold separately) | |
| Oil pan drain plug gasket | 2018 - 2021 models | GM 12616850 |
| Oil fill cap | ACDelco FC261 | |
| Fuel filter | ACDelco TP1015 | |
| Serpentine belt, single alternator | 2017 - 2019 models | ACDelco 12656797 |
| 2020 - 2021 models | ACDelco 12675892 | |
| Serpentine belt, dual alternator | 2017 - 2019 models | ACDelco 6K1395A |
| 2020 - 2021 models | ACDelco 12675893 | |
| Water pump drive belt | 2020 - 2021 models | ACDelco 12675896 |
| Thermostat, front | 2017 - 2019 models | ACDelco 12T99D |
| 2020 - 2021 models | ACDelco 131-197 | |
| Thermostat, rear | 2017 - 2019 models | ACDelco 121-131 |
| 2020 - 2021 models | ACDelco 131-197 | |
| Thermostat seal | GM 98280281 | |
| Thermostat housing gasket | GM 12643149 | |
| Coolant reservoir cap | 2017 - 2018 models | ACDelco RC120 or ACDelco 12R05 |
| 2019 - 2021 models | GM 13502353 | |
| Upper radiator hose | 2017 - 2019 models | ACDelco 84094878 |
| 2020 - 2021 models | GM 84813629 | |
| Lower radiator hose | 2017 - 2019 models | ACDelco 84401398 & ACDelco 84376513 |
| 2020 - 2021 models | ACDelco 84645096 | |
| Glow plug | ACDelco 68G | |
| Automatic transmission filter, external | Allison 6 speed | ACDelco TF950, Allison 29539579 |
| GM-Allison 10 speed | ACDelco TF928 | |
| Automatic transmission filter, internal | Allison 6 speed | GM 29542833 |
| Transmission pan gasket | Allison 6 speed | GM 29549684 |
| GM-Allison 10 speed | GM 24297922 | |
| Front differential gasket | 2020 - 2021 models | GM 84756927 or GM 20768579 |
| Rear differential gasket | 2017 - 2019 models | GM 23445892 |
| 2020 - 2021 models | GM 84757352 | |
6.6L Duramax L5P Oil & Fluid Specs, Capacities
| Item | Oil/Fluid Specification | Capacity [1] | |
| Engine oil [2] | Ambient temp > 0° F | SAE 15W-40 API CJ-4 or CK-4 Recommend Amsoil Max Duty 15W-40 synthetic diesel oil |
10 quarts w/ filter change |
| Ambient temp < 0° F (acceptable in all temps) |
SAE 5W-40 API CJ-4 or CK-4 Recommend Amsoil Max Duty 5W-40 synthetic diesel oil |
||
| Engine coolant | 50/50 solution DEX-COOL engine coolant concentrate and distilled water (GM DEX-COOL 12346290) |
7.525 - 7.85 gallons | |
| Automatic transmission fluid | Allison 6 speed | GM DEXRON VI automatic transmission fluid (ACDelco 10-9243) |
7.4 quarts service refill 12.7 quarts total capacity |
| GM-Allison 10 speed | GM DEXRON ULV automatic transmission fluid (ACDelco 10-4107) |
20.6 - 22.1 quarts total capacity | |
| Transfer case fluid | 2017 - 2019 models | GM DEXRON VI automatic transmission fluid (ACDelco 10-9243) Recommend Amsoil Signature Series FE synthetic ATF |
1.6 quarts |
| 2020+ models | 2.4 quarts | ||
| Front differential fluid | SAE 75W-90 synthetic gear oil Recommend Amsoil Severe Gear 75W-90 synthetic gear oil |
1.8 quarts | |
| Rear differential fluid | SAE 75W-90 synthetic gear oil Recommend Amsoil Severe Gear 75W-90 synthetic gear oil |
4.4 - 5.0 quarts | |
| Diesel exhaust fluid | DEF meeting ISO 22241-1 specifications or equivalent, GM 19286291/ACDelco 10-4022 | 7.0 gallons | |
[1] Oil and fluid capacities are nominal; always fill to proper fluid indicator level (i.e. dipstick), fill plug height, or applicable level identifier. Vehicle should be parked on a level surface when checking or adjusting fluid level.
[2] 15W-40 engine oil preferred in ambient temperatures above 0° F. 5W-40 is acceptable in all ambient temperatures, but only preferred (and required) when ambient temperatures are below 0° F.