Code Details
| Display code | SPN 4364 FMI 18 |
|---|---|
| SPN | 4364 |
| FMI | 18 |
| OEM code | None listed |
| Manufacturer | International |
| System | Aftertreatment — SCR |
| Component | SCR catalyst / DEF dosing system / NOx sensors / DEF quality |
| 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 uses a selective catalytic reduction system that injects diesel exhaust fluid into the exhaust upstream of the SCR catalyst to convert NOx into nitrogen and water. The ECM monitors the SCR conversion efficiency by comparing upstream and downstream NOx sensor readings and sets SPN 4364 FMI 18 when the efficiency falls below the moderately severe threshold. On the A26 — used in International LT and RH Series trucks for linehaul applications — DEF quality issues, dosing injector faults, and SCR catalyst degradation from oil contamination are the most commonly seen causes. The ECM inducement sequence for this fault escalates from warning to derate if the efficiency deficit is not corrected within the specified time period.
SPN 4364 is Aftertreatment 1 SCR Conversion Efficiency; FMI 18 indicates valid data below the moderately severe low threshold. On the A26 (GHG17 platform), the ECM calculates SCR efficiency from upstream and downstream NOx sensor data. International Servicemaxx provides live data for both NOx sensor positions, the DEF dosing system, SCR temperature readings, and the inducement timer status. The Servicemaxx DEF dosing injector test confirms injector function. Refractometer testing provides a direct DEF quality verification independent of the on-board sensor. Inducement timer data in Servicemaxx shows the current derate stage and time remaining before the next escalation.
Common Symptoms
- Check engine and aftertreatment lamps on
- SCR efficiency or DEF system warning on the driver display
- Engine derate if the inducement sequence has advanced
- DEF consumption change relative to expected rate
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- DEF quality below specification
- DEF dosing injector clogged or failing
- SCR catalyst degraded from oil contamination or high mileage
- NOx sensor failure or inaccuracy
- DEF pump or supply circuit fault
First Checks
- Test DEF with a refractometer — confirm 32.5% +/- 1.5% urea
- Connect Servicemaxx — view live upstream and downstream NOx sensor data
- Run the Servicemaxx DEF dosing injector actuation test
- Inspect DEF supply lines and filter for crystallization or restriction
- Check inducement timer status in Servicemaxx
Can I Keep Driving?
The A26 inducement timer may be progressing toward a performance derate. Address DEF and dosing system faults 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
FAQ
What happens if I ignore SPN 4364 FMI 18 on the International A26?
Ignoring SPN 4364 FMI 18 allows the inducement timer to continue running. Under GHG17 regulations, the inducement sequence advances to progressively more severe derates — typically limiting vehicle speed and then further reducing power — until the fault is corrected. At the most severe inducement levels, the vehicle may be limited to speeds that make linehaul operation impractical. The inducement timer cannot be reset without correcting the root cause and performing the appropriate Servicemaxx reset procedure.
Is the A26 SCR system compatible with all commercially available DEF?
The A26 SCR system is designed for ISO 22241-compliant DEF with a 32.5% urea concentration. All ISO 22241-compliant DEF products meeting the purity and concentration specification should be compatible. The concern arises when non-compliant DEF is used, or when contamination from an incorrect fluid (such as water, fuel, or a cleaning agent) enters the DEF tank. The on-board DEF quality sensor can detect some contaminants, and a refractometer test confirms urea concentration independently.
Can SPN 4364 FMI 18 on the A26 set from short-trip operation where the SCR catalyst does not reach operating temperature?
Yes. The SCR catalyst on the A26 requires a minimum operating temperature to effectively convert NOx using the ammonia derived from DEF. In applications with very short trip cycles where the aftertreatment system does not reach full operating temperature before the engine is shut down, the ECM may detect low efficiency during the warmup phase that accumulates over many short cycles. Servicemaxx SCR temperature data can confirm whether the catalyst temperature is reaching the operating range during representative driving cycles.