Code Details
| Display code | SPN 3246 FMI 0 |
|---|---|
| SPN | 3246 |
| FMI | 0 |
| OEM code | None listed |
| Manufacturer | Mack |
| System | Aftertreatment �?DPF |
| Component | DPF outlet temperature sensor / regen system / dosing injector |
| Source address | Unknown or not applicable |
| Severity | medium |
| Review status | source backed |
| Source confidence | medium |
| Last reviewed | 2026-06-12 |
Plain-English Meaning
During a DPF regeneration event, the dosing injector adds fuel to raise exhaust temperature and burn accumulated soot. The DPF outlet temperature sensor confirms that heat is reaching and exiting the filter. When SPN 3246 FMI 0 sets on the Mack MP8, the outlet temperature exceeded the expected maximum, which can indicate an overfueling dosing injector, a regen that will not terminate, or a stuck active regen condition.
SPN 3246 FMI 0 is Aftertreatment 1 Outlet Gas Temperature above normal range. VCADS Pro (PTT) logs regen events and temperature profiles for the MP8 aftertreatment. The regen history is the key diagnostic tool for evaluating whether SPN 3246 FMI 0 appeared during a normal regen that ran to the correct endpoint, or during a regen that could not terminate due to a stuck dosing injector or control fault.
Common Symptoms
- DPF temperature fault code logged during or after regeneration
- May accompany dosing injector-related fault codes
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Active regen with higher than normal soot load requiring extended burn time
- Dosing injector stuck open or overfueling
- Regen not terminating at the normal endpoint
- DPF outlet temperature sensor fault
First Checks
- Connect VCADS Pro (PTT) and review the regen history including temperature profiles
- Check for companion SPN 3249 (inlet temp) codes and compare inlet-to-outlet differential
- Inspect the dosing injector for carbon deposits or stuck-open condition
- Review the fault event snapshot for vehicle speed and conditions at the time of fault
Can I Keep Driving?
Driveable in most cases. Address if recurrent or if dosing injector faults accompany the code.
Related Codes
Related Lookup Pages
Sources
- Mack Trucks Service Support Public Resources Mack Trucks Inc. · oem · accessed 2026-06-11 · confidence medium
Source: Mack Trucks Inc., Mack Trucks Service Support Public Resources. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - Volvo Trucks / Mack Trucks Technical Support Volvo Trucks North America / Mack Trucks Inc. · oem · accessed 2026-06-10 · confidence medium
Source: Volvo Trucks North America / Mack Trucks Inc., Volvo Trucks / Mack Trucks Technical Support. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - SAE J1939 Standards Collection SAE International · official · accessed 2026-05-05 · confidence medium
Source: SAE International, SAE J1939 Standards Collection. This page paraphrases factual fields only and is not a substitute for the original document.
Open source
FAQ
Is SPN 3246 FMI 0 on the Mack MP8 a sign of a damaged DPF?
Not automatically. SPN 3246 FMI 0 can occur during a normal high-load regen on an otherwise healthy DPF. However, a recurrent pattern of high outlet temperatures combined with poor regen efficiency (soot load not dropping after a regen) may indicate that the DPF substrate has been damaged and is not filtering properly. VCADS Pro regen history and DPF differential pressure data help confirm this.
How does the Mack MP8 dosing injector get stuck open?
The dosing injector introduces diesel fuel into the exhaust stream. Carbon deposits from fuel combustion can accumulate on the injector tip over time, preventing it from closing fully. This allows fuel to continue entering the exhaust even when the ECM has not commanded a regen, causing sustained high exhaust temperature. Periodic inspection or replacement of the dosing injector per Mack maintenance guidelines helps prevent this.
Can VCADS Pro force a Mack MP8 parked regen to clear high soot load that contributes to high outlet temperature?
Yes. VCADS Pro (PTT) can initiate a forced stationary regen on the Mack MP8, which allows the aftertreatment system to burn accumulated soot in a controlled manner. If soot load is the primary cause of the high regen temperature, a successful forced regen should resolve the root condition. If outlet temperature remains abnormally high after a successful regen, investigate the dosing injector and sensor circuit.