Cummins fault code 5938
DPF 1 Conditions Not Met for Active Regeneration: special instructions
What it means
Cummins' description: Diesel Particulate Filter 1 Conditions Not Met for Active Regeneration – Condition Exists.
SPN 3750 is Diesel Particulate Filter 1 Conditions Not Met for Active Regeneration. FMI 14 means the fault requires specific troubleshooting steps from Cummins service information.
The DPF traps soot from the exhaust and burns it off during regeneration. Pressure and temperature sensors before and after the filter tell the ECM how loaded the filter is and whether regeneration is working.
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 DPF lamp comes on solid and the truck drives normally. Running it at highway speed for 20-30 minutes, or doing a parked regen if your truck supports it, clears it.
Schedule a repair
The DPF lamp is flashing or the code keeps coming back after regens. Plan service soon. The filter is loading faster than it can clean itself and something upstream may be wrong.
Stop and get help
Stop lamp on, power derated, or a strong exhaust smell or smoke. Don't keep driving. A plugged DPF can overheat, crack, and take the turbo or engine with it.
Common causes
The sensor reading itself is out of range or the condition is real, so look at the system:
- Too much idling or short trips, so the DPF never gets hot enough to regenerate
- Regeneration interrupted or inhibited (inhibit switch on, key-off mid regen)
- Upstream problem making excess soot: leaking injector, EGR or boost fault
- DPF full of ash and due for cleaning or replacement
- Face-plugged or cracked DOC/DPF
What you can check before calling
- Check the dash for a regen or DPF lamp and whether a regen is being requested
- Make sure the regen inhibit switch isn't turned on
- Look at the sensor hoses and wiring on top of the DPF for melted or loose lines
- Note how much the truck idles versus runs at highway speed
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: DPF regeneration explained: passive, active and forced.
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
Related DPF codes
- 6265 SPN 3936 FMI 7
DPF System: not responding / out of adjustment - 6551 SPN 3610 FMI 3
DPF Outlet Pressure Sensor Circuit: circuit voltage high / shorted high - 6552 SPN 3610 FMI 4
DPF Outlet Pressure Sensor Circuit: circuit voltage low / shorted low - 6553 SPN 3610 FMI 2
DPF Outlet Pressure: erratic or intermittent signal - 6568 SPN 3695 FMI 2
Regeneration Inhibit Switch: erratic or intermittent signal - 6596 SPN 3713 FMI 31
DPF Active Regeneration Inhibited Due to System Timeout: condition exists
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 5938 mean?
Cummins fault code 5938 is J1939 SPN 3750 FMI 14: Diesel Particulate Filter 1 Conditions Not Met for Active Regeneration – Condition Exists. In plain terms: dpf 1 conditions not met for active regeneration: special instructions.
Can I keep driving with Cummins code 5938?
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 5938?
SPN 3750 identifies the part or system (Diesel Particulate Filter 1 Conditions Not Met for Active Regeneration). FMI 14 describes the type of failure: special instructions.
What usually causes Cummins code 5938?
The most common causes are: too much idling or short trips, so the DPF never gets hot enough to regenerate; regeneration interrupted or inhibited (inhibit switch on, key-off mid regen); upstream problem making excess soot: leaking injector, EGR or boost fault.
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.