The Detroit DT12 automated manual transmission has been a key component in many Freightliner and Western Star trucks, providing efficiency and reliability. Like any system, it generates fault codes to help diagnose and resolve potential issues.
DT12 Overview
- Transmission Type: Automated Manual Transmission (AMT)
- Gear Speeds: 12 forward speeds, 2 reverse speeds
- Torque Capacity: Up to 2,050 lb-ft
- Integrated Features: Intelligent Powertrain Management (IPM), eCoast, and Skip Shift
- Applications: Freightliner Cascadia, Western Star 5700XE, and select vocational trucks
Fault Codes for Detroit DT12 (2013-2020)
Below is a comprehensive list of fault codes you may encounter on a Detroit DT12 transmission, which covers model years 2013-2020. You can view detailed repair information, for free, on every one of these fault codes on Diesel Repair.
Diesel Repair also includes other essential information such as fault code-to-part number cross-references, wiring diagrams, labor time guides, and step-by-step replacement instructions—everything you need to properly troubleshoot your Detroit DT12 transmission.
Detroit DT12 (2013-2020) Fault Codes
For additional technical support, troubleshooting guides, and repair information, visit Diesel Repair. Keeping your DT12 transmission in peak condition ensures optimal performance and longevity.
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| Fault | SPN | FMI | 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 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 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 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 521484 FMI 2 | 521484 | 2 | Rail Shaft Position Sensor Data Erratic |
| SPN 521484 FMI 5 | 521484 | 5 | Rail Shaft 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 5 | 521488 | 5 | Split Shaft Position Sensor Open Circuit |
| SPN 521490 FMI 4 | 521490 | 4 | Output Shaft Speed Sensor Circuit Failed Low |
| 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 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 5 | 521752 | 5 | Rail Solenoid Out – Low Priority Circuit Failed High |
| SPN 524286 FMI 1 | 524286 | 1 | Automatic Gear Selection – Automatic Mode Not Available |
| SPN 524286 FMI 4 | 524286 | 4 | Automatic Gear Selection: Gear Shift Not Plausible |