Code Details
| Display code | SPN 3364 FMI 1 |
|---|---|
| SPN | 3364 |
| FMI | 1 |
| OEM code | None listed |
| Manufacturer | International, Navistar |
| System | Aftertreatment �?DEF quality |
| Component | DEF quality sensor / DEF tank / DEF fluid |
| Source address | Unknown or not applicable |
| Severity | high |
| Review status | source backed |
| Source confidence | medium |
| Last reviewed | 2026-06-12 |
Plain-English Meaning
The International A26 SCR aftertreatment system monitors DEF quality to ensure proper NOx reduction. DEF that is too dilute, contaminated, or degraded cannot reduce NOx to the required level, causing emissions non-compliance. SPN 3364 FMI 1 means the quality sensor detected below-specification fluid. This triggers an inducement sequence that will reduce engine power if the quality issue is not corrected. The fault is common in International LT, HV, and HX series trucks with the A26.
SPN 3364 FMI 1 is DEF Quality below normal range. On International A26 with ACM2.1 aftertreatment control, the DEF quality sensor uses ultrasonic measurement. Diamond Logic Builder (DLB) and International Servicemaxx both display the DEF quality sensor reading and can confirm sensor function. FMI 1 indicates a valid below-normal reading from a functioning sensor.
Common Symptoms
- DEF quality warning on the International instrument cluster
- SCR efficiency fault may follow if poor DEF continues to be dosed
- Inducement escalation with distance-based power reduction if not corrected
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- DEF diluted with water during the fill process
- DEF degraded from excessive heat storage or extended shelf time
- Water contamination from a failed DEF tank filler cap seal
- Incorrect fluid filled in the DEF tank
- DEF quality sensor fault
First Checks
- Test DEF sample with a refractometer �?should read 31.8�?3.2% urea concentration
- If out of specification, drain the DEF tank completely and refill with fresh ISO 22241 DEF
- Connect Diamond Logic Builder or Servicemaxx and confirm the DEF quality sensor reading changes after a fresh refill
- Clear the fault code and allow a drive cycle to confirm the new DEF quality is within specification
- Inspect the DEF filler cap and neck for contamination sources
Can I Keep Driving?
Continued operation with poor DEF will trigger inducement. Drain and refill promptly.
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 - 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 the International A26 use the same DEF system as the MaxxForce 13?
The International A26 uses a newer generation ACM2.1 aftertreatment architecture, different from the MaxxForce 13 generation system. The A26 aftertreatment system is more closely aligned with current EPA compliance requirements. The DEF quality sensor technology and diagnostic approach are similar to current industry standards, but A26-specific service procedures apply.
Can Diamond Logic Builder distinguish between a bad DEF quality sensor and actually poor DEF quality?
Yes. Diamond Logic Builder displays the DEF quality sensor reading as a live value. If the reading shows low quality and a refractometer test confirms the DEF is out of specification, the DEF is the problem. If the refractometer test confirms the DEF is within specification but the sensor continues to read low, the quality sensor is the fault. DLB can also run sensor diagnostics to check the sensor circuit.
What DEF brand is safe to use in an International A26 truck?
Any DEF meeting the ISO 22241 standard is suitable for the International A26. API-certified DEF products sold at truck stops in North America under brand names including BlueDEF, Def-X, and fleet-branded products all meet ISO 22241 if certified. The key requirement is the ISO 22241 specification �?not a specific brand.