Cummins fault code 3868
DEF Quality: abnormal update rate
What it means
Cummins' description: Aftertreatment Diesel Exhaust Fluid Quality - Abnormal update rate.
SPN 3364 is Aftertreatment 1 Diesel Exhaust Fluid Tank 1 Quality. FMI 9 means data the ECM expects to receive over the network stopped arriving or arrived too slowly. Usually a communication, power, or module problem.
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
- 1685 SPN 3364 FMI 4
DEF Quality Sensor Circuit: circuit voltage low / shorted low - 1686 SPN 3364 FMI 3
DEF Quality Sensor Circuit: circuit voltage high / shorted high - 1714 SPN 3364 FMI 13
DEF Quality: out of calibration - 1715 SPN 3364 FMI 11
DEF Quality: root cause not known - 3866 SPN 3364 FMI 1
DEF Quality: reading below normal (most severe) - 3867 SPN 3364 FMI 18
DEF Quality: reading below normal (moderately severe) - 3876 SPN 3364 FMI 7
DEF Quality Sensor: not responding / out of adjustment - 3877 SPN 3364 FMI 12
DEF Quality Sensor: bad device or component
Related DEF codes
- 3755 SPN 5394 FMI 2
DEF Dosing Valve: erratic or intermittent signal - 3713 SPN 5491 FMI 7
DEF Line Heater Relay: not responding / out of adjustment - 3596 SPN 4334 FMI 2
DEF Pressure Sensor: erratic or intermittent signal - 4155 SPN 5746 FMI 3
DEF Dosing Unit Heater Relay: circuit voltage high / shorted high - 4156 SPN 5746 FMI 4
DEF Dosing Unit Heater Relay: circuit voltage low / shorted low - 4157 SPN 4376 FMI 7
DEF Return Valve: not responding / out of adjustment
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 3868 mean?
Cummins fault code 3868 is J1939 SPN 3364 FMI 9: Aftertreatment Diesel Exhaust Fluid Quality - Abnormal update rate. In plain terms: def quality: abnormal update rate.
Can I keep driving with Cummins code 3868?
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 3868?
SPN 3364 identifies the part or system (Aftertreatment 1 Diesel Exhaust Fluid Tank 1 Quality). FMI 9 describes the type of failure: abnormal update rate.
What usually causes Cummins code 3868?
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.