Detroit DT12 Transmission
Specs, gear ratios, oil change interval and warranty
Detroit (Daimler Truck)
The Detroit DT12 is a 12-speed automated manual transmission. Detroit lists it for the Freightliner Cascadia, M2 112 Plus and 114SD Plus. Its on-highway page shows three torque ratings: 2,250, 2,050 and 1,650 lb-ft. Detroit's fluid guide sets oil drain intervals from 180,000 miles for severe duty to 400,000 miles for light line-haul. Trucks with Detroit's Maintenance System can run up to 600,000 miles.
Detroit (Daimler Truck) published the Detroit DT12 figures in its own documents. Last reviewed November 3, 2026.
What are the Detroit DT12 specs?
| Type | Automated manual (AMT) |
|---|---|
| Speeds | 12 forward, 4 reverse |
| Models on Detroit's on-highway page | DT12-HE (highest efficiency), a middle rating, and DT12-HL (lightweight) |
| Maximum input torque | 2,250 lb-ft (HE), 2,050 lb-ft (middle), 1,650 lb-ft (HL) |
| Gross combination weight limit | 160,000 lb (HE), 140,000 lb (middle), 80,000 lb (HL) |
| Weight | Detroit gives no weight in pounds. It says the DT12-HL is up to 125 lb lighter than the other models. |
Compare the Detroit DT12 with the others in the transmission specs reference, and see which truck it sits in on the truck model specs.
What should you check before you spec or buy a truck with the Detroit DT12?
- Match the rating to your weight. Detroit lists gross combination weight limits of 160,000 lb for the DT12-HE, 140,000 lb for the middle rating and 80,000 lb for the DT12-HL. The rating on the truck sets what it is built to pull.
- Check the model year before you buy oil. For 2017 and newer, Detroit lists MB 235.16 or MB 235.11 as service fill. For 2016 and older, MB 235.11 only, and MB 235.16 is not approved.
- Ask for the service record and compare it with Detroit's drain interval for the truck's duty, from 180,000 to 400,000 miles. Get the transmission warranty in writing, because the Detroit pages we read do not state one.
Which DT12 ratings does Detroit list?
Detroit's on-highway page lists three DT12 ratings. It names the HE and the HL. It does not name the middle one. Detroit's fluid guide says H means highway, HL means highway lightweight and HE means highway efficiency.
| Rating | Max input torque | GCW limit | Gear ratio range | Engines | Trucks |
|---|---|---|---|---|---|
| DT12-HE | 2,250 lb-ft | 160,000 lb | 14.56–0.78 overdrive; 18.80–1.00 direct drive | DD13, DD15, DD16 | Cascadia, M2 112 Plus |
| Middle rating | 2,050 lb-ft | 140,000 lb | 11.64–0.78 overdrive; 14.93–1.00 direct drive | DD13, DD15 | Cascadia |
| DT12-HL | 1,650 lb-ft | 80,000 lb | 11.67–0.78 overdrive; 14.93–1.00 direct drive | DD13 | Cascadia, M2 112 Plus, 114SD Plus |
What fluid does the Detroit DT12 use, and how often do you change it?
Detroit's fluid guide approves two transmission fluids for the DT12. They are Mercedes-Benz specs: MB 235.16 (75W-85) and MB 235.11 (75W-90). Detroit says to use only approved fluids, in the right viscosity for the truck's model year.
| Factory fill, 2017 and newer | MB 235.16 (75W-85) |
|---|---|
| Factory fill, 2016 and older | MB 235.11 (75W-90) |
| Service fill, 2017 and newer | Either MB 235.16 (75W-85) or MB 235.11 (75W-90) |
| Service fill, 2016 and older | MB 235.11 (75W-90) only. MB 235.16 is not approved. |
| Refill, 2020 and newer C-box | 8.9 qt (8.4 L) |
| Refill, 2017 B-box and A-box | 8.5 qt (8.0 L) and 12.7 qt (12.0 L) |
| Refill, 2016 and older B-box and A-box | 11.6 qt (11.0 L) and 15.9 qt (15.0 L) |
| Add if the cooler and lines are drained | 1.0–1.1 qt |
| Add for a PTO | 0.5–0.6 qt rear PTO; 1.7 qt small side PTO; 3.7 qt large side PTO |
These are Detroit's drain intervals for the DT12 in the US and Canada, model year 2017 and newer. Use the shorter of the miles or the years.
| Duty cycle | Interval |
|---|---|
| Line haul up to 80,000 lb | 400,000 miles or 5 years |
| Short haul: line haul 80,000–140,000 lb, pickup and delivery, or transfer refuse up to 140,000 lb | 300,000 miles or 5 years |
| Severe: line haul over 140,000 lb, heavy haul and other severe work | 180,000 miles or 3 years |
| With Detroit's Maintenance System: efficient long haul (C-box) | Up to 600,000 miles |
| With Detroit's Maintenance System: long haul and short haul | Up to 400,000 miles |
| With Detroit's Maintenance System: severe | Up to 180,000 miles |
- Detroit's Maintenance System started on new truck orders placed on or after January 21, 2020. It sets the interval from how the truck is used. Older orders do not have it.
- Detroit defines long haul as more than 60,000 miles a year with little stop-and-go. Short haul is 30,000 to 60,000 miles a year. Severe is up to 30,000 miles a year or hard conditions such as construction, farm, logging, mining or refuse.
- DT12 Classic, model year 2016 and older: Detroit lists 400,000 miles or 3 years with an air-to-oil cooler for trucks under 80,000 lb, and 300,000 miles or 3 years with other coolers. Over 80,000 lb it lists 300,000 miles or 2 years with an air-to-oil cooler, and 200,000 miles or 2 years with other coolers.
- Detroit says it has no transmission fluid sample kits.
- Detroit says it is not responsible for repairs caused by skipped maintenance or fluids that do not meet its specs.
Put your Detroit DT12 service on a schedule with the maintenance scheduler. If a warning light comes on, decode it with the fault code lookup.
What warranty does the Detroit DT12 have?
Warranty, as the maker lists it
- The Detroit pages we read do not state a transmission warranty term. Check the written warranty that came with the truck.
Which engines and trucks go with the Detroit DT12?
Detroit pairs the DT12-HE with the DD13, DD15 and DD16, the middle rating with the DD13 and DD15, and the DT12-HL with the DD13. It lists the Freightliner Cascadia for all three ratings, the M2 112 Plus for the HE and HL, and the 114SD Plus for the HL.
Fitted in the Freightliner Cascadia, Freightliner M2 112 Plus and Freightliner 114SD Plus.
What Detroit (Daimler Truck) claims
- Detroit says the DT12-HE is built for maximum efficiency and further downspeeding, and that the DT12-HL is built to save weight. It gives no mpg or percent figures for either.
What is not published about the Detroit DT12?
- The DT12's weight in pounds
- A transmission warranty term on the pages we read
- Any fuel savings in mpg or percent
- A price. Detroit sells it as part of the truck's spec.
There is no public, independent failure-rate data for any heavy-duty transmission, including the Detroit DT12. This page does not rank reliability. It lists what the maker publishes: ratings, ratios, fluid, service intervals and warranty. For a used truck, ask for the service records and check the oil and clutch history.
How does the Detroit DT12 compare with other transmissions?
Each transmission guide on this site follows the same format and the same sourcing rule, so you can read the Detroit DT12 next to the others. We do not name a winner.
- PACCAR TX-12Automated manual, 12-speed
- Volvo I-ShiftAutomated manual, 12-, 13- or 14-speed
- Eaton Cummins EndurantAutomated manual, 11-, 12- or 18-speed
Side-by-side comparisons with the Detroit DT12
Detroit DT12 frequently asked questions
What oil does a Detroit DT12 transmission use?+
Detroit approves two fluids for the DT12: MB 235.16 (75W-85) and MB 235.11 (75W-90). Trucks from model year 2017 on ship with MB 235.16 and may be serviced with either. Trucks from 2016 and older use MB 235.11 only. Detroit says to use only approved fluids in the Detroit DT12.
How much fluid does a DT12 transmission hold?+
Detroit lists about 8.9 qt (8.4 L) for a 2020 C-box DT12, and 8.5 qt (8.0 L) or 12.7 qt (12.0 L) for 2017 B-box and A-box units. Older DT12s hold 11.6 qt or 15.9 qt. Add 1.0 to 1.1 qt if you drain the cooler and lines, and extra for a PTO. Fill until the oil is level with the bottom of the fill hole.
How often should you change the oil in a DT12?+
For 2017 and newer trucks in the US and Canada, Detroit lists 400,000 miles or 5 years for line haul up to 80,000 lb, 300,000 miles or 5 years for short haul, and 180,000 miles or 3 years for severe duty. Trucks with the Maintenance System can go up to 600,000 miles. Use whichever limit comes first.
What are the DT12 gear ratios?+
Detroit's page gives ranges, not a gear-by-gear table. The DT12-HE runs 14.56 to 0.78 in overdrive and 18.80 to 1.00 in direct drive. The middle rating and the DT12-HL run 11.64 or 11.67 to 0.78 in overdrive and 14.93 to 1.00 in direct drive.
How long does a DT12 transmission last?+
Detroit does not publish a life figure for the DT12, and the pages we read give no transmission warranty term. What Detroit does publish is its drain interval, up to 600,000 miles with the Maintenance System. Oil changes on time are the one part you control. Treat any life claim you see elsewhere as an opinion.
Is the DT12 any good?+
That depends on the truck and its service history, and no independent failure study exists for the Detroit DT12. What can be checked is the rating: the HE handles 2,250 lb-ft and 160,000 lb combined weight, and the HL is the lightest at 1,650 lb-ft and 80,000 lb. On a used truck, ask for the oil change records and the model year, because older units use a different fluid.
Sources for the Detroit DT12
Run a Detroit DT12 truck? Let a dispatcher handle the rest.
Grow Trucking finds loads, negotiates rates and does the paperwork for owner-operators and small fleets. Tell us about your Detroit DT12 truck and we will show you how we can help.
Also: About Grow Trucking · Refer a carrier · Trucking blog
Ratings, intervals and warranty terms for the Detroit DT12 change by model year and configuration. Confirm the exact figures for a specific truck against Detroit (Daimler Truck)'s current documents and your written warranty before you make a purchase or maintenance decision.
Free tools for a Detroit DT12 truck
Keep the Detroit DT12 serviced on time, decode its fault codes and check a truck before you buy.
- Preventive Maintenance SchedulerTrack Detroit DT12 oil changes by odometer for your duty cycle.
- Diesel Fault Code Lookup (SPN/FMI)Decode the SPN/FMI fault codes the Detroit DT12 reports.
- Breakdown Cost EstimatorEstimate what a Detroit DT12 breakdown costs in repairs and lost revenue.
- Used Truck Inspection ChecklistCheck the Detroit DT12 and clutch before you buy a used truck.