Code Details
| Display code | SPN 1761 FMI 1 |
|---|---|
| SPN | 1761 |
| FMI | 1 |
| OEM code | None listed |
| Manufacturer | PACCAR |
| 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 PACCAR MX-13 uses a DEF system to reduce nitrogen oxides through selective catalytic reduction. When the DEF tank level drops below the minimum acceptable threshold, the engine management system begins the operator inducement sequence. A warning lamp appears on the dash first; if the tank is not refilled within the programmed distance, the ECM applies a torque restriction and eventually a road speed cap. Topping off the DEF tank and resetting the fault with PACCAR ESA resolves the condition.
SPN 1761 is Aftertreatment 1 DEF Tank Level in the J1939 standard. FMI 1 indicates the sensor value is below the normal operating range. On PACCAR MX-13 engines, the DEF module integrates the level sensor, heating element, and pump into a single unit mounted in or on the DEF tank. The EMS (Engine Management System) monitors the DEF level signal and triggers the inducement sequence when the level falls below the calibrated threshold. PACCAR ESA (Electronic Service Analyst) provides live DEF level readings, inducement stage data, and the ability to reset the inducement counter after the fault is corrected.
Common Symptoms
- Amber DEF or aftertreatment warning lamp on the Kenworth or Peterbilt instrument cluster
- DEF level low message on the in-cab display or telematics unit
- Progressive torque reduction if the low-level condition persists
- Inducement status readable in PACCAR ESA or connected telematics
- Speed restriction in the final inducement stage until DEF is restored and the fault is cleared
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- DEF tank level below the programmed low-level threshold
- DEF level sensor or float assembly failed, reporting incorrect low reading
- Wiring or connector fault in the DEF level sensor circuit
- DEF tank venting issue causing incorrect pressure-based level reading
- Tank drained by a technician without being refilled before the truck was returned to service
First Checks
- Confirm the actual DEF level using the instrument cluster DEF gauge or by inspecting the tank directly
- Add fresh, quality DEF if the level is confirmed low and check whether the fault clears after a short drive
- Connect PACCAR ESA and navigate to the aftertreatment section to compare the DEF level sensor output to the known physical level
- Check for related codes such as SPN 3361 (supply pressure) or SPN 1761 FMI 18 (level sensor range) that could indicate a sensor failure versus a genuine low-level condition
- Inspect the DEF module wiring harness and connector for corrosion, chafing, or loose terminals if the fault persists with a full tank
- Perform the inducement reset in PACCAR ESA after the DEF level is verified and the root cause is addressed
Can I Keep Driving?
The MX-13 will initially continue operating with SPN 1761 FMI 1 active, but the inducement escalates over accumulated mileage, adding torque and speed restrictions. Restoring the DEF level promptly and resetting the inducement in PACCAR ESA prevents any power limitation.
Related Codes
Related Lookup Pages
Sources
- PACCAR / Kenworth / Peterbilt Service Support — MX Engine Resources PACCAR Inc. · oem · accessed 2026-06-11 · confidence medium
Source: PACCAR Inc., PACCAR / Kenworth / Peterbilt Service Support — MX Engine Resources. 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
Does SPN 1761 FMI 1 on the PACCAR MX-13 indicate the DEF tank is completely empty?
Not necessarily. FMI 1 means the level reading is below the normal operating range, which typically corresponds to the low-level warning threshold rather than a completely empty tank. The exact threshold varies by calibration. Topping off the tank to at least one-quarter full is a practical first step to resolve the fault before connecting PACCAR ESA for further diagnosis.
How do I reset the inducement on the PACCAR MX-13 after adding DEF?
Adding DEF alone may allow the fault to self-clear after a drive cycle if the sensor confirms the level is now above the threshold. If the inducement counter has advanced to a higher stage, the counter may require a manual reset using PACCAR ESA. Connect ESA, navigate to the aftertreatment or inducement reset function, confirm the DEF level is adequate, and execute the reset procedure.
Can I use a generic OBD-II scanner to reset SPN 1761 FMI 1 on the MX-13?
Generic OBD-II scanners typically lack access to the PACCAR-specific aftertreatment data parameters and inducement reset functions. While a generic J1939 reader may display the fault code, the inducement reset on PACCAR MX-13 engines requires PACCAR ESA or a compatible heavy-duty diagnostic tool with PACCAR-specific software to complete the reset procedure properly.