5 Detroit DT12 diagnostic codes on file. Each shows the symptom for free — unlock the full diagnosis, repair steps, and field insights with a free account.
| Code | System | Symptom | Fix |
|---|---|---|---|
| SPN 520970 FMI 07 | Clutch / AMT | Transmission Won't Go into Gear / Air Hiss | Unlock |
| SPN 521002 FMI 07 | Pneumatics / Clutch | Clutch Grabs Suddenly / Rolling Jerk | Unlock |
| SPN 521476 FMI 03 | Speed Sensing | Erratic Shifting / Skipping Gears | Unlock |
| SPN 521481 FMI 04 | Thermal / Sensor | Fan Roars Continuously / Trans Alert | Unlock |
| SPN 521487 FMI 05 | Actuation / Splitter | Stuck in Low Range / Max Speed 45 km/h | Unlock |
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