PACCAR MX-11 SPN 3246 FMI 0 — DPF Outlet Temperature Very High

Code Details

Plain-English Meaning

The PACCAR MX-11 aftertreatment system uses a temperature sensor at the DPF outlet to monitor exhaust gas temperature exiting the diesel particulate filter. During normal active regeneration events, the DPF outlet temperature rises as soot is oxidized inside the filter and then returns to the normal exhaust temperature range once the regen cycle completes. When SPN 3246 FMI 0 is set, the DPF outlet sensor is reporting a temperature above the critical high limit — a level indicating an uncontrolled thermal condition inside the DPF rather than a normal peak regen temperature. On the MX-11, this fault most commonly results from the hydrocarbon dosing injector (HC doser) not seating properly when commanded off, delivering raw diesel fuel into the exhaust system after the regen cycle should have ended. Fuel injector internal leakage and very high soot loads are additional contributing factors. The ACM responds to this fault by inhibiting active regeneration and may apply a derate to reduce exhaust heat generation.

SPN 3246 is Aftertreatment 1 Diesel Particulate Filter Outlet Gas Temperature; FMI 0 indicates valid sensor data above the highest severity threshold. On the PACCAR MX-11, the aftertreatment control module uses multiple temperature measurement points across the aftertreatment assembly to manage regen cycles and protect components from thermal damage. PACCAR ESA provides live data views of all aftertreatment temperature sensors and captures freeze-frame parameter data at the moment of fault detection, which allows a technician to reconstruct the thermal conditions at fault set. The ESA HC doser actuation test confirms whether the injector opens and closes correctly on command. Comparing DPF inlet versus DPF outlet temperature readings from the freeze-frame data helps determine whether the over-temperature condition originated within the DPF itself (suggesting uncontrolled HC oxidation inside the filter) or was driven by an upstream temperature source entering the DPF at an already-elevated level.

Common Symptoms

• Aftertreatment warning or stop engine lamp on the instrument panel
• Engine power derate imposed by the ACM
• Active regeneration halted or prevented
• Exhaust odor suggesting unburned or partially burned fuel
• Multiple aftertreatment DTCs present alongside SPN 3246 FMI 0 in ESA

Possible Causes

Possible causes may include the items below. The list is not a parts diagnosis.

• HC dosing injector not seating or closing when commanded off, delivering unmetered fuel to the exhaust
• Fuel injector internal leak on one or more cylinders contributing fuel to the exhaust stream
• High DPF soot load causing an extended regen with elevated thermal output
• DPF outlet temperature sensor failed or drifted out of calibration toward a high reading
• Excessive oil consumption contributing hydrocarbon loading in the exhaust and DPF

First Checks

• Connect PACCAR ESA and read the freeze-frame snapshot for SPN 3246 FMI 0 to determine the outlet temperature peak and the state of other aftertreatment parameters at fault set
• View live aftertreatment temperature data to compare the DPF outlet reading against DOC inlet, DPF inlet, and SCR inlet sensor values under steady-state no-regen conditions
• Perform the ESA HC doser actuation test to verify the hydrocarbon dosing injector opens and closes on command and does not continue to deliver fuel when commanded off
• Use ESA cylinder balance data to check for any cylinder showing abnormally high fuel contribution that may indicate internal injector leakage into the exhaust
• Physically inspect the DPF outlet area for thermal discoloration or damage signs — substrate damage from a previous thermal event may explain recurring high outlet temperatures even after other repairs

Can I Keep Driving?

A significant derate is likely when SPN 3246 FMI 0 is active. Do not attempt a forced parked regen while this fault is present. Identify and correct the source of excess hydrocarbon input into the aftertreatment system before resuming regen activity.

Related Lookup Pages

• FMI 0 explanation
• Aftertreatment fault codes
• Search this code