Code Details
| Display code | SPN 3031 FMI 1 |
|---|---|
| SPN | 3031 |
| FMI | 1 |
| OEM code | None listed |
| Manufacturer | International |
| System | Aftertreatment — SCR |
| Component | DEF tank / DEF tank temperature sensor / DEF tank heater |
| Source address | Unknown or not applicable |
| Severity | medium |
| Review status | source backed |
| Source confidence | medium |
| Last reviewed | 2026-06-12 |
Plain-English Meaning
The International A26 aftertreatment system includes a DEF tank heater to prevent the DEF from freezing in cold weather conditions. DEF that falls below its freezing point cannot be pumped to the dosing injector, interrupting SCR function. When the DEF tank temperature sensor reads below the normal operational range, the ECM sets SPN 3031 FMI 1 and alerts the operator. On A26-equipped LT Series trucks operating in cold northern climates, overnight DEF freezing during winter months is a common cause of this fault. The tank heater system is designed to thaw the DEF after a cold start during the engine warmup period. If the heater has failed, the DEF temperature will not rise during warmup, and SCR efficiency faults will develop as DEF dosing continues to be unavailable.
SPN 3031 is Aftertreatment 1 DEF Tank Temperature; FMI 1 indicates valid data below the normal operational range. On the A26, the DEF tank heater uses engine coolant to warm the DEF. International Servicemaxx provides live DEF tank temperature data and related DEF system information. Monitoring the temperature trend during warmup is the key diagnostic indicator of heater function. A temperature that rises progressively toward normal during warmup confirms the heater is functioning. A static temperature tracking ambient after extended engine operation indicates a heater coolant supply fault.
Common Symptoms
- DEF temperature warning lamp on the instrument cluster in cold weather
- SCR efficiency or DEF dosing faults developing alongside SPN 3031 FMI 1
- Engine derate if DEF dosing is not restored and the inducement sequence advances
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- DEF frozen from cold overnight ambient temperatures below -11 degrees C
- DEF tank heater coolant supply failure or disconnection
- DEF tank heater element failure
- DEF tank temperature sensor failure producing a false below-normal reading
First Checks
- Assess overnight parking temperature and determine if freezing conditions occurred
- Allow extended warmup and monitor DEF tank temperature in Servicemaxx
- If temperature does not rise, inspect the coolant supply to the DEF tank heater for blockage or disconnection
- Confirm the coolant lines at the DEF tank heater are warm during engine operation
- Test the sensor plausibility against ambient temperature conditions
Can I Keep Driving?
The A26 is driveable with SPN 3031 FMI 1 active. DEF dosing will resume after the DEF thaws. A malfunctioning heater should be repaired to prevent recurring DEF system disruption in cold weather operations.
Related Codes
Related Lookup Pages
Sources
- International Trucks Service Support Public Resources International Trucks / Navistar International · oem · accessed 2026-06-11 · confidence medium
Source: International Trucks / Navistar International, International Trucks Service Support Public Resources. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - Navistar Engine Diagnostic Trouble Code Body Builder References Navistar / International Truck Body Builder · oem · accessed 2026-05-05 · confidence medium
Source: Navistar / International Truck Body Builder, Navistar Engine Diagnostic Trouble Code Body Builder References. This page paraphrases factual fields only and is not a substitute for the original document.
Open source
FAQ
What is the DEF freezing point and does it change with different DEF brands on the A26?
ISO 22241-compliant DEF has a standard composition of 32.5% urea and 67.5% deionized water, which gives it a consistent freezing point of approximately -11 degrees Celsius (12 degrees Fahrenheit) regardless of the brand. All compliant DEF from different manufacturers should freeze at the same temperature because the composition is standardized. DEF that has been diluted with additional water will have a lower urea concentration and a slightly higher freezing point, closer to the freezing point of water, which means it can freeze at somewhat warmer temperatures than specification DEF.
Will the International A26 enter an idle shutdown with SPN 3031 FMI 1 active?
SPN 3031 FMI 1 itself does not trigger an idle shutdown. The idle shutdown on the A26 is controlled by idle shutdown timer settings in the ECM, which are set by the fleet or customer configuration. The SCR inducement derate from a prolonged SCR efficiency fault (which develops if DEF dosing remains unavailable) can limit speed and power but does not typically cause an idle shutdown. The vehicle can be operated to a service location while monitoring the instrument cluster for any additional fault escalation.
Can I prevent SPN 3031 FMI 1 on the International A26 in cold climate fleets?
Proactive measures to reduce SPN 3031 FMI 1 frequency in cold climate fleets include ensuring the DEF tank heater system is inspected at every major service interval, parking the vehicle in a heated facility when possible during extreme cold, and verifying the DEF tank level is kept adequately full so the heater has sufficient contact with the DEF to warm it effectively. A very low DEF level means the heater has less DEF mass to warm and the DEF at the pickup may freeze faster. Maintaining the DEF level above the halfway mark in cold weather reduces the risk of the pickup-level DEF freezing before the heater can act.