Cummins fault code 5278
DEF Dosing System Frozen: condition exists
What it means
Cummins' description: Aftertreatment 1 Diesel Exhaust Fluid Dosing System Frozen - Condition Exists.
SPN 6802 is DEF Dosing System Frozen. FMI 31 means the ECM has confirmed the condition described in the code is happening.
DEF is sprayed into the exhaust ahead of the SCR catalyst to break down NOx. The system includes the tank, level and temperature sensors, a quality sensor, heaters for cold weather, a pump or dosing unit, lines and the doser.
What the lamp means
An amber (yellow) warning lamp means the engine can usually keep running, but the fault should be repaired soon, ideally the same day.
Green, yellow, red: three ways this can look
The same code can be a quick fix or a reason to shut down. Match your situation to the closest example.
Keep an eye on it
The DEF level warning is on and the truck runs normally. Topping off with fresh DEF clears it.
Schedule a repair
Amber lamp or a DEF quality or dosing code that comes back after filling. Get it checked soon. If left alone, the system will start counting down toward a derate.
Stop and get help
Blinking lamp with a derate countdown, or the truck is already limited to low speed. That's an EPA inducement. It won't fix itself and it can leave a truck stuck at 5 mph.
Common causes
The sensor reading itself is out of range or the condition is real, so look at the system:
- DEF tank low or empty
- Contaminated, diluted or old DEF (water, coolant, diesel, or DEF older than about a year)
- Crystallized DEF clogging the doser, lines or filter
- Weak pump or blocked DEF filter
- Frozen DEF with a heater not working
What you can check before calling
- Check the DEF level and top off with fresh, sealed DEF
- Look for white crystal buildup around the doser, lines and tank
- If DEF was recently added, think about whether it could have been mixed with water or something else
- Note whether the code shows up only in cold weather
Clearing the code without fixing the cause usually brings it right back, and on emissions systems it can restart derate timers. For the bigger picture, read our guide: DEF warning lights and derate: what diesel drivers need to know.
Engines and sources
Listed by Cummins for: QSB 6.7, QSL 9, QSX 15, QSB 4.5, QSF 3.8 (With SCR), QSG 12. Cummins uses the same fault code numbers across its electronic engines, including on-highway models like the ISB/B6.7, ISL/L9 and ISX/X15, though not every code applies to every engine or software level. Source: Cummins Tier 4 Fault Codes. Always confirm with Cummins service information (QuickServe) for your engine serial number.
Related DEF codes
- 4842 SPN 3364 FMI 15
DEF Quality: reading above normal (least severe) - 4769 SPN 1761 FMI 10
DEF Tank Level Sensor: abnormal rate of change - 4768 SPN 3521 FMI 11
DEF Property: root cause not known - 4753 SPN 520716 FMI 4
DEF Dosing Valve 1 Heater: circuit voltage low / shorted low - 4752 SPN 520716 FMI 3
DEF Dosing Valve 1 Heater: circuit voltage high / shorted high - 4745 SPN 3515 FMI 11
DEF Temperature 2: root cause not known
Look up another code
Cummins fault code (like 1922), J1939 SPN and FMI (like SPN 3251 FMI 0), or an OBD-II code (like P0420).
Questions
What does Cummins fault code 5278 mean?
Cummins fault code 5278 is J1939 SPN 6802 FMI 31: Aftertreatment 1 Diesel Exhaust Fluid Dosing System Frozen - Condition Exists. In plain terms: def dosing system frozen: condition exists.
Can I keep driving with Cummins code 5278?
Usually for a short time, if the engine runs normally and no other warnings are on. Get it diagnosed soon, because many amber codes lead to a derate if ignored. Look at the green, yellow and red examples on this page to judge your situation.
What is the SPN and FMI for Cummins code 5278?
SPN 6802 identifies the part or system (DEF Dosing System Frozen). FMI 31 describes the type of failure: condition exists.
What usually causes Cummins code 5278?
The most common causes are: dEF tank low or empty; contaminated, diluted or old DEF (water, coolant, diesel, or DEF older than about a year); crystallized DEF clogging the doser, lines or filter.
Diesel down in the Midlands?
We work on Cummins-powered pickups, vans and medium-duty trucks across Lexington, Columbia and the Midlands, on site at your yard or roadside.