Cummins fault code 4739
DEF Tank Level Sensor: root cause not known
What it means
Cummins' description: Aftertreatment 1 Diesel Exhaust Fluid Tank Level Sensor - Root Cause Not Known.
SPN 1761 is Aftertreatment 1 Diesel Exhaust Fluid Tank Level. FMI 11 means the ECM detected a fault in this system but can't pin down the exact type. Further testing is needed.
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.
Same SPN, other failure types
- 1668 SPN 1761 FMI 4
DEF Tank Level Sensor Circuit: circuit voltage low / shorted low - 1669 SPN 1761 FMI 3
DEF Tank Level Sensor Circuit: circuit voltage high / shorted high - 1673 SPN 1761 FMI 1
DEF Tank Level: reading below normal (most severe) - 1699 SPN 1761 FMI 2
DEF Tank Level Sensor: erratic or intermittent signal - 3497 SPN 1761 FMI 17
DEF Tank Level: reading below normal (least severe) - 3498 SPN 1761 FMI 18
DEF Tank Level: reading below normal (moderately severe) - 4677 SPN 1761 FMI 9
SAE J1939 Multiplexing PGN Timeout Error: abnormal update rate - 4679 SPN 1761 FMI 5
DEF Tank Level Sensor Circuit: circuit open / current low
Related DEF codes
- 4737 SPN 3031 FMI 11
DEF Tank Temperature: root cause not known - 4736 SPN 3031 FMI 6
DEF Tank Temperature Sensor Circuit: circuit grounded / current high - 4743 SPN 3515 FMI 5
DEF Temperature 2 Sensor Circuit: circuit open / current low - 4744 SPN 3515 FMI 6
DEF Temperature 2 Sensor Circuit: circuit grounded / current high - 4745 SPN 3515 FMI 11
DEF Temperature 2: root cause not known - 4731 SPN 3031 FMI 13
DEF Tank Temperature Sensor: out of calibration
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 4739 mean?
Cummins fault code 4739 is J1939 SPN 1761 FMI 11: Aftertreatment 1 Diesel Exhaust Fluid Tank Level Sensor - Root Cause Not Known. In plain terms: def tank level sensor: root cause not known.
Can I keep driving with Cummins code 4739?
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 4739?
SPN 1761 identifies the part or system (Aftertreatment 1 Diesel Exhaust Fluid Tank Level). FMI 11 describes the type of failure: root cause not known.
What usually causes Cummins code 4739?
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.