Code Details
| Display code | SPN 1761 FMI 1 |
|---|---|
| SPN | 1761 |
| FMI | 1 |
| OEM code | None listed |
| Manufacturer | Cummins |
| System | Aftertreatment — DEF supply |
| Component | DEF tank level sensor / DEF supply module |
| Source address | Unknown or not applicable |
| Severity | medium |
| Review status | source backed |
| Source confidence | medium |
| Last reviewed | 2026-06-12 |
Plain-English Meaning
The Cummins ISB 6.7 is a widely used medium-duty engine found in delivery trucks, school buses, and vocational equipment. Like larger Cummins engines, it uses a DEF system to meet emissions requirements. When the DEF level drops below the calibrated minimum, the ECM begins an inducement sequence with progressive power restrictions. A refill and an INSITE reset resolve most low-level conditions, though a faulty level sensor can produce the same symptom on a full tank.
SPN 1761 is Aftertreatment 1 DEF Tank Level in J1939. FMI 1 indicates a below-normal reading from the level sensor. On Cummins CM2350 ISB 6.7 engines, the DEF tank module includes the level sensor, quality sensor, and heater in an integrated assembly. The ACM monitors the level signal and initiates the inducement sequence when it falls below the calibrated threshold. The inducement uses distance-based stages identical in structure to larger Cummins engines such as the ISX15. INSITE provides DEF level data, the inducement stage, and the reset function.
Common Symptoms
- Amber DEF warning lamp on the instrument panel
- DEF level alert or SCR system message on the dash display
- Possible reduced power under load if the inducement has advanced past the initial stage
- Inducement stage visible in Cummins INSITE or connected telematics
- Speed or torque restriction in advanced inducement stages
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- DEF tank depleted below the calibrated low-level threshold
- DEF level sensor failed or stuck at a low reading
- Wiring or connector fault in the DEF level sensor circuit
- DEF consumed faster than expected due to a dosing system fault
- DEF tank drained during service without being refilled
First Checks
- Confirm the actual DEF level using the instrument cluster or by physically checking the tank before pursuing electrical diagnosis
- Add fresh DEF if the level is low and observe whether the warning clears after driving
- Connect Cummins INSITE and read the DEF level sensor output to compare against the physical level
- Review for companion codes such as SPN 3364 (DEF quality) or SPN 3480 (dosing injector) that might indicate additional aftertreatment problems
- Inspect the DEF tank module connector and wiring if the tank is confirmed full but the fault remains active
- Perform the inducement reset in INSITE after confirming the DEF level is adequate and the root cause is resolved
Can I Keep Driving?
The ISB 6.7 can operate initially with SPN 1761 FMI 1 active, but the inducement will escalate with accumulated mileage. Torque derates and potential speed restrictions follow. Prompt DEF refill and an INSITE reset prevent any power limitation from affecting the vehicle.
Related Codes
Related Lookup Pages
Sources
- Cummins INSITE Service Tool — Public Reference Documentation Cummins Inc. · oem · accessed 2026-06-11 · confidence medium
Source: Cummins Inc., Cummins INSITE Service Tool — Public Reference Documentation. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - QuickServe Online Cummins Inc. · oem · accessed 2026-05-05 · confidence medium
Source: Cummins Inc., QuickServe Online. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - SAE J1939 Standards Collection SAE International · official · accessed 2026-05-05 · confidence medium
Source: SAE International, SAE J1939 Standards Collection. This page paraphrases factual fields only and is not a substitute for the original document.
Open source
FAQ
Is the DEF inducement sequence on the ISB 6.7 the same as on the ISX15?
The ISB 6.7 uses the same Cummins CM2350 ECM family and the same aftertreatment inducement framework as the ISX15 and X15. The structure of the inducement sequence — initial warning, torque derate, speed restriction — is the same across these Cummins engine families. The specific distance thresholds may differ by calibration, but the diagnostic and reset procedures using INSITE are the same.
Do school buses and medium-duty trucks with the ISB 6.7 have the same DEF system as on-highway trucks?
The ISB 6.7 uses the same Cummins aftertreatment architecture in all applications, but DEF tank size and module placement can differ based on the vehicle chassis. School bus and vocational applications may have smaller DEF tanks, which can lead to more frequent low-level conditions on vehicles that do not follow the same fueling intervals as long-haul trucks. Regular DEF checks at each fueling stop are recommended for these applications.
Can the Cummins ISB 6.7 inducement be bypassed in an emergency situation?
The inducement system is part of the emissions compliance framework and cannot be legitimately disabled. Attempting to modify or bypass inducement logic violates federal emissions regulations and can result in fines and compliance issues for fleet operators. The appropriate response to an inducement condition is to refill the DEF tank, correct any underlying system faults, and perform the reset using INSITE.