The Detroit DT12 automated manual transmission, used in model years 2024 to 2025, is engineered for optimal fuel efficiency, smooth shifting, and intelligent driver assistance. Paired with Detroit’s latest engines, the DT12 is built to handle heavy loads while reducing driver fatigue and improving vehicle performance. With advanced electronic controls, this transmission system provides fault codes that help technicians quickly diagnose transmission-related issues, ensuring minimal downtime and more efficient repairs.
Whether you’re a fleet manager, diesel technician, or maintenance supervisor, having access to fault codes, wiring diagrams, and repair procedures is critical to keeping vehicles on the road and avoiding costly transmission failures.
DT12 Transmission Overview
- Type: Automated Manual Transmission (AMT)
- Speeds: 12 forward, 2 reverse
- Torque Capacity: Up to 2,050 lb-ft
- Integrated Features: Intelligent Powertrain Management (IPM), Hill Start Aid, Creep Mode
- Applications: Freightliner Cascadia, Western Star 57X, and other Detroit-powered Class 8 trucks
🔗 Get FREE Fault Code Information for all makes and models on Diesel Repair → Diesel Repair
Detroit DT12 (2024–2025) Fault Codes
Below is a comprehensive list of fault codes for the Detroit DT12 transmission, covering model years 2024 and 2025. For full diagnostics — including troubleshooting guides, wiring diagrams, repair procedures, and labor time estimates — visit Diesel Repair, the industry-leading platform for diesel drivetrain diagnostics.
| Fault | PID | SPN | FMI | SID | Title |
| SPN 520451 FMI 11 | 520451 | 11 | TCM Internal Error | ||
| SPN 520451 FMI 18 | 520451 | 18 | TCM Internal Error | ||
| SPN 520451 FMI 3 | 520451 | 3 | TCM Internal Voltage Too High | ||
| SPN 520451 FMI 4 | 520451 | 4 | TCM Internal Voltage Too Low | ||
| SPN 520486 FMI 13 | 520486 | 13 | Tilt Sensor – Not Learned | ||
| SPN 520486 FMI 14 | 520486 | 14 | Tilt Sensor – Special Instruction | ||
| SPN 520490 FMI 12 | 520490 | 12 | TCM Internal Failure | ||
| SPN 520491 FMI 12 | 520491 | 12 | TCM Internal Failure | ||
| SPN 520492 FMI 12 | 520492 | 12 | TCM Power Down Interrupted (EEPROM – Data Not Saved) | ||
| SPN 520713 FMI 5 | 520713 | 5 | TCM Battery Supply Voltage Open Circuit | ||
| SPN 520714 FMI 5 | 520714 | 5 | TCM Battery Supply Voltage Open Circuit | ||
| SPN 520715 FMI 5 | 520715 | 5 | Battery Supply Voltage Open Circuit | ||
| SPN 520716 FMI 5 | 520716 | 5 | TCM Battery Supply Voltage Open Circuit | ||
| SPN 520717 FMI 3 | 520717 | 3 | TCM Battery Supply Voltage High | ||
| SPN 520717 FMI 4 | 520717 | 4 | TCM Battery Supply Voltage Low | ||
| SPN 520718 FMI 3 | 520718 | 3 | TCM Ignition Supply Voltage High | ||
| SPN 520718 FMI 4 | 520718 | 4 | TCM Ignition Supply Voltage Low | ||
| SPN 520960 FMI 7 | 520960 | 7 | Unable to Shift Split Group into Retracted Position | ||
| SPN 520962 FMI 7 | 520962 | 7 | Clutch Apply – Air Pressure Inconsistent | ||
| SPN 520964 FMI 13 | 520964 | 13 | Gearbox Not Learned | ||
| SPN 520966 FMI 1 | 520966 | 1 | Transmission Oil Pressure Too Low | ||
| SPN 520970 FMI 7 | 520970 | 7 | Clutch – Unable to Open Fully | ||
| SPN 520971 FMI 7 | 520971 | 7 | Clutch Actual Position Unknown | ||
| SPN 520976 FMI 14 | 520976 | 14 | TCM Software – Not Compatible with Vehicle | ||
| SPN 520977 FMI 14 | 520977 | 14 | Shift Position Error – Learn Procedure | ||
| SPN 520978 FMI 14 | 520978 | 14 | TCM Learn – Actuator Distance Error | ||
| SPN 520979 FMI 14 | 520979 | 14 | TCM Learn – Clutch Error | ||
| SPN 520980 FMI 14 | 520980 | 14 | TCM Learn – Shift Actuator Learn Error | ||
| SPN 520981 FMI 7 | 520981 | 7 | AMT Clutch Control – Air Supply Pressure Error | ||
| SPN 520982 FMI 0 | 520982 | Clutch Learn – Minimum Distance Error | |||
| SPN 520982 FMI 1 | 520982 | 1 | Clutch Learn – Maximum Distance Error | ||
| SPN 520982 FMI 13 | 520982 | 13 | Clutch Learn – Out of Range | ||
| SPN 520982 FMI 2 | 520982 | 2 | Clutch Learn – Data Invalid | ||
| SPN 520984 FMI 14 | 520984 | 14 | TCM EEPROM Checksum Error | ||
| SPN 520985 FMI 0 | 520985 | AMT Clutch Close Fast Solenoid – On Time Upper Limit Reached | |||
| SPN 520986 FMI 0 | 520986 | AMT Clutch Close Slow Solenoid – On Time Upper Limit Reached | |||
| SPN 520987 FMI 0 | 520987 | AMT Clutch Open Fast Solenoid – On Time Upper Limit Reached | |||
| SPN 520988 FMI 0 | 520988 | AMT Clutch Open Fast Solenoid – On Time Upper Limit Reached | |||
| SPN 520994 FMI 14 | 520994 | 14 | Transmission for Setting the Correct Model Type when Reprogramming | ||
| SPN 520995 FMI 14 | 520995 | 14 | TCM Transmission Type Error | ||
| SPN 520996 FMI 14 | 520996 | 14 | Output Shaft Tone Wheel – Tooth Count Not Valid | ||
| SPN 520997 FMI 14 | 520997 | 14 | Transmission Type Software Error | ||
| SPN 520998 FMI 15 | 520998 | 15 | TCM Detected Clutch Kiss Point is Out of Calibration Limit | ||
| SPN 520999 FMI 7 | 520999 | 7 | AMT Clutch Control – Mechanical Error | ||
| SPN 521001 FMI 0 | 521001 | Clutch – Zero Point Too High | |||
| SPN 521001 FMI 1 | 521001 | 1 | Clutch – Zero Point Too Low | ||
| SPN 521002 FMI 7 | 521002 | 7 | AMT Clutch Control – Actuator Supply Pressure Error | ||
| SPN 521003 FMI 7 | 521003 | 7 | AMT Clutch Control – Actuator Release Pressure Error | ||
| SPN 521005 FMI 14 | 521005 | 14 | Output Shaft Speed – Not Plausible | ||
| SPN 521006 FMI 14 | 521006 | 14 | Countershaft Speed – Not Plausible | ||
| SPN 521007 FMI 14 | 521007 | 14 | Main Shaft Speed – Not Plausible | ||
| SPN 521030 FMI 14 | 521030 | 14 | TCM Incorrect Parameter Set | ||
| SPN 521031 FMI 14 | 521031 | 14 | TCM Incorrect Parameter Set for Current Software Version | ||
| SPN 521032 FMI 15 | 521032 | 15 | AMT Clutch Close Fast Solenoid – On Time Lower Limit Reached | ||
| SPN 521033 FMI 15 | 521033 | 15 | AMT Clutch Close Slow Solenoid – On Time Lower Limit Reached | ||
| SPN 521034 FMI 15 | 521034 | 15 | AMT Clutch Open Fast Solenoid – On Time Lower Limit Reached | ||
| SPN 521035 FMI 15 | 521035 | 15 | AMT Clutch Open Slow Solenoid – On Time Lower Limit Reached | ||
| SPN 521041 FMI 14 | 521041 | 14 | Clutch Type – Parameter Invalid | ||
| SPN 521042 FMI 14 | 521042 | 14 | Clutch Actuator Type – Parameter Invalid | ||
| SPN 521043 FMI 14 | 521043 | 14 | TCM – PCM Error | ||
| SPN 521045 FMI 14 | 521045 | 14 | Main Shaft – Incorrect Rotation Direction | ||
| SPN 521049 FMI 7 | 521049 | 7 | Split Pin Sticking in the Retracted Position | ||
| SPN 521050 FMI 1 | 521050 | 1 | Transmission Oil Pressure Too Low | ||
| SPN 521221 FMI 19 | 521221 | 19 | No CAN Communication | ||
| SPN 521222 FMI 19 | 521222 | 19 | TCM – No CAN Data Received from CPC | ||
| SPN 521224 FMI 19 | 521224 | 19 | No CAN Data Received from MCM | ||
| SPN 521473 FMI 3 | 521473 | 3 | Gear Rail Split Position Sensors Supply Voltage Open or High | ||
| SPN 521473 FMI 4 | 521473 | 4 | Gear Rail Split Position Sensors Supply Voltage Low | ||
| SPN 521474 FMI 3 | 521474 | 3 | Clutch Position Sensor Supply Voltage Open or High | ||
| SPN 521474 FMI 4 | 521474 | 4 | Clutch Position Sensor Supply Voltage Low | ||
| SPN 521476 FMI 2 | 521476 | 2 | Main Shaft Speed – Data Erratic TCM Over Temperature | ||
| SPN 521476 FMI 3 | 521476 | 3 | Main Shaft Speed Sensor Circuit Failed High | ||
| SPN 521476 FMI 4 | 521476 | 4 | Main Shaft Speed Sensor Circuit Failed Low | ||
| SPN 521476 FMI 5 | 521476 | 5 | Main Shaft Speed Sensor Open Circuit | ||
| SPN 521477 FMI 2 | 521477 | 2 | Countershaft Speed – Data Erratic TCM Over Temperature | ||
| SPN 521477 FMI 3 | 521477 | 3 | Countershaft Speed Sensor Circuit Failed High | ||
| SPN 521477 FMI 4 | 521477 | 4 | Countershaft Speed Sensor Circuit Failed Low | ||
| SPN 521477 FMI 5 | 521477 | 5 | Countershaft Speed Sensor Open Circuit | ||
| SPN 521478 FMI 9 | 521478 | 9 | Gear Oil Pressure Sensor Without Function | ||
| SPN 521481 FMI 11 | 521481 | 11 | Transmission Oil Temperature Out-of-Operating Range | ||
| SPN 521481 FMI 18 | 521481 | 18 | Transmission Oil Temperature – Drifted Low | ||
| SPN 521481 FMI 3 | 521481 | 3 | Transmission Oil Temperature Sensor Circuit Failed Open or High | ||
| SPN 521481 FMI 4 | 521481 | 4 | Transmission Oil Temperature Sensor Circuit Failed Low | ||
| SPN 521483 FMI 16 | 521483 | 16 | AMT – Over Temperature | ||
| SPN 521484 FMI 2 | 521484 | 2 | Rail Shaft Position Sensor Data Erratic | ||
| SPN 521484 FMI 5 | 521484 | 5 | Rail Shaft Position Sensor Open Circuit | ||
| SPN 521485 FMI 12 | 521485 | 12 | Gear Rail Split Sensor – Defective Component | ||
| SPN 521485 FMI 2 | 521485 | 2 | Gear Rail Split Sensor – Gear Position Erratic | ||
| SPN 521485 FMI 3 | 521485 | 3 | Gear Rail Split Sensor – Shorted High | ||
| SPN 521486 FMI 2 | 521486 | 2 | Clutch Position Sensor – Data Erratic | ||
| SPN 521486 FMI 5 | 521486 | 5 | Clutch Position Sensor – Open Circuit | ||
| SPN 521487 FMI 3 | 521487 | 3 | Range Position Sensor Circuit Failed High | ||
| SPN 521487 FMI 4 | 521487 | 4 | Range Position Sensor Circuit Failed Low | ||
| SPN 521487 FMI 5 | 521487 | 5 | Range Position Sensor Open Circuit | ||
| SPN 521488 FMI 2 | 521488 | 2 | Split Position Sensor – Data Erratic | ||
| SPN 521488 FMI 5 | 521488 | 5 | Split Shaft Position Sensor Open Circuit | ||
| SPN 521490 FMI 4 | 521490 | 4 | Output Shaft Speed Sensor Circuit Failed Low | ||
| SPN 521491 FMI 2 | 521491 | 2 | Clutch Position Sensor – Signal Invalid | ||
| SPN 521491 FMI 5 | 521491 | 5 | Clutch Position Sensor Signal – Open | ||
| SPN 521497 FMI 13 | 521497 | 13 | Clutch Position – Signal 1 and 2 Mismatch | ||
| SPN 521498 FMI 13 | 521498 | 13 | Clutch Position – Signal 2 and 1 Mismatch | ||
| SPN 521516 FMI 11 | 521516 | 11 | Transmission Air Pressure – Out of Operating Range | ||
| SPN 521518 FMI 9 | 521518 | 9 | Transmission Oil Pressure Sensor Circuit Not Responding | ||
| SPN 521729 FMI 3 | 521729 | 3 | TCM Driver GrS_G2 – Failed High | ||
| SPN 521729 FMI 4 | 521729 | 4 | TCM Driver GrS_G2 – Failed Low | ||
| SPN 521729 FMI 5 | 521729 | 5 | TCM Driver GrS_G2 – Failed Open | ||
| SPN 521730 FMI 3 | 521730 | 3 | TCM Driver GrS_G2 – Failed High | ||
| SPN 521730 FMI 4 | 521730 | 4 | TCM Driver GrS_G2 – Failed Low | ||
| SPN 521730 FMI 5 | 521730 | 5 | TCM Driver GrS_G2 – Failed Open | ||
| SPN 521731 FMI 3 | 521731 | 3 | TCM Driver GrS_G3 – Failed High | ||
| SPN 521731 FMI 4 | 521731 | 4 | TCM Driver GrS_G3 – Failed Low | ||
| SPN 521731 FMI 5 | 521731 | 5 | TCM Driver GrS_G3 – Failed Open | ||
| SPN 521732 FMI 3 | 521732 | 3 | TCM Driver GrS_K1 – Failed High | ||
| SPN 521732 FMI 4 | 521732 | 4 | TCM Driver GrS_K1 – Failed Low | ||
| SPN 521732 FMI 5 | 521732 | 5 | TCM Driver GrS_K1 – Failed Open | ||
| SPN 521733 FMI 3 | 521733 | 3 | TCM Driver GrS_K2 – Failed High | ||
| SPN 521733 FMI 4 | 521733 | 4 | TCM Driver GrS_K2 – Failed Low | ||
| SPN 521733 FMI 5 | 521733 | 5 | TCM Driver GrS_K2 – Failed Open | ||
| SPN 521736 FMI 3 | 521736 | 3 | AMT Clutch Open Slow Solenoid – Circuit Failed High | ||
| SPN 521736 FMI 4 | 521736 | 4 | AMT Clutch Open Slow Solenoid – Circuit Failed Low | ||
| SPN 521736 FMI 5 | 521736 | 5 | AMT Clutch Open Slow Solenoid – Open Circuit | ||
| SPN 521737 FMI 3 | 521737 | 3 | AMT Clutch Open Fast Solenoid – Circuit Failed High | ||
| SPN 521737 FMI 4 | 521737 | 4 | AMT Clutch Open Fast Solenoid – Circuit Failed Low | ||
| SPN 521737 FMI 5 | 521737 | 5 | AMT Clutch Open Fast Solenoid – Open Circuit | ||
| SPN 521738 FMI 3 | 521738 | 3 | AMT Clutch Close Slow Solenoid – Circuit Failed High | ||
| SPN 521738 FMI 4 | 521738 | 4 | AMT Clutch Close Slow Solenoid – Circuit Failed Low | ||
| SPN 521738 FMI 5 | 521738 | 5 | AMT Clutch Close Slow Solenoid – Open Circuit | ||
| SPN 521739 FMI 3 | 521739 | 3 | AMT Clutch Close Fast Solenoid – Circuit Failed High | ||
| SPN 521739 FMI 4 | 521739 | 4 | AMT Clutch Close Fast Solenoid – Circuit Failed Low | ||
| SPN 521739 FMI 5 | 521739 | 5 | AMT Clutch Close Fast Solenoid – Open Circuit | ||
| SPN 521740 FMI 3 | 521740 | 3 | Range High Position Solenoid – Circuit Failed High | ||
| SPN 521740 FMI 4 | 521740 | 4 | Range High Position Solenoid – Circuit Failed Low | ||
| SPN 521740 FMI 5 | 521740 | 5 | Range High Position Solenoid – Open Circuit | ||
| SPN 521741 FMI 3 | 521741 | 3 | Range Low Position Solenoid – Circuit Failed High | ||
| SPN 521741 FMI 4 | 521741 | 4 | Range Low Position Solenoid – Circuit Failed Low | ||
| SPN 521741 FMI 5 | 521741 | 5 | Range Low Position Solenoid – Open Circuit | ||
| SPN 521742 FMI 3 | 521742 | 3 | Split Low Position Solenoid – Circuit Failed High | ||
| SPN 521742 FMI 4 | 521742 | 4 | Split Low Position Solenoid – Circuit Failed Low | ||
| SPN 521742 FMI 5 | 521742 | 5 | Split Low Position Solenoid – Open Circuit | ||
| SPN 521743 FMI 3 | 521743 | 3 | Split High Position Solenoid – Circuit Failed High | ||
| SPN 521743 FMI 4 | 521743 | 4 | Split High Position Solenoid – Circuit Failed Low | ||
| SPN 521743 FMI 5 | 521743 | 5 | Split High Position Solenoid – Open Circuit | ||
| SPN 521744 FMI 3 | 521744 | 3 | Countershaft Solenoid – Circuit Failed High | ||
| SPN 521744 FMI 4 | 521744 | 4 | Countershaft Solenoid – Circuit Failed Low | ||
| SPN 521744 FMI 5 | 521744 | 5 | Countershaft Solenoid – Open Circuit | ||
| SPN 521745 FMI 3 | 521745 | 3 | Gear Solenoid Out- Circuit Failed High | ||
| SPN 521745 FMI 4 | 521745 | 4 | Gear Solenoid Out – Circuit Failed Low | ||
| SPN 521745 FMI 5 | 521745 | 5 | Gear Solenoid Out – Open Circuit | ||
| SPN 521746 FMI 3 | 521746 | 3 | Gear Solenoid In – Circuit Failed High | ||
| SPN 521746 FMI 4 | 521746 | 4 | Gear Solenoid In – Circuit Failed Low | ||
| SPN 521746 FMI 5 | 521746 | 5 | Gear Solenoid In – Open Circuit | ||
| SPN 521747 FMI 3 | 521747 | 3 | Rail Solenoid Out – Circuit Failed High | ||
| SPN 521747 FMI 4 | 521747 | 4 | Rail Solenoid Out – Circuit Failed Low | ||
| SPN 521747 FMI 5 | 521747 | 5 | Rail Solenoid Out – Open Circuit | ||
| SPN 521748 FMI 3 | 521748 | 3 | Rail Solenoid In – Circuit Failed High | ||
| SPN 521748 FMI 4 | 521748 | 4 | Rail Solenoid In – Circuit Failed Low | ||
| SPN 521748 FMI 5 | 521748 | 5 | Rail Solenoid In – Open Circuit | ||
| SPN 521751 FMI 3 | 521751 | 3 | Rail Solenoid In – Low Priority Circuit Failed High | ||
| SPN 521751 FMI 5 | 521751 | 5 | Rail Solenoid In – Low Priority Open Circuit | ||
| SPN 521752 FMI 3 | 521752 | 3 | Rail Solenoid Out – Low Priority Circuit Failed High | ||
| SPN 521752 FMI 5 | 521752 | 5 | Rail Solenoid Out – Low Priority Circuit Failed High | ||
| SPN 521762 FMI 7 | 521762 | 7 | No Clutch Values Available | ||
| SPN 524286 FMI 1 – GHG14 | 524286 | 1 | Automatic Gear Selection – Automatic Mode Not Available | ||
| SPN 524286 FMI 4 – GHG14 | 524286 | 4 | Automatic Gear Selection: Gear Shift Not Plausible | ||
| SPN 524286 FMI 6 – GHG14 | 524286 | 6 | CPC is incorrectly parameterized | ||
| SPN 524286 FMI 7 | 524286 | 7 | Common Powertrain Controller (CPC) has detected inconsistent driveline speed | ||
| SPN 524295 FMI 1 – GHG14 | 524295 | 1 | This diagnostic is a test. |
To stay ahead of downtime and get your trucks back on the road faster, explore Diesel Repair for expert troubleshooting, technical documents, and everything you need to service your DT12 transmission.