International A26 SPN 3364 FMI 1 �?DEF Quality Below Threshold

Code Details

Plain-English Meaning

The International A26 is International's proprietary 12.4L engine used in LT and RH Series trucks. Like other modern heavy-duty diesel engines, it requires DEF with approximately 32.5% urea concentration for its SCR system to reduce NOx. When the quality sensor detects a lower concentration, the engine ECM logs this code and begins the inducement countdown. On International LT Series and RH Series trucks with the A26, the DEF quality sensor is integrated into the DEF tank module alongside the level sensor and supply pump. ServiceMaxx displays all DEF module parameters together. On the A26, the DEF supply pump is inside the DEF tank module, and a supply pump failure can produce a DEF quality fault because the dosing injector is not receiving adequate flow. ServiceMaxx can run a DEF supply pump commanded flow test to confirm whether the pump is the fault source or whether the quality sensor itself is the issue.

SPN 3364 is Aftertreatment 1 DEF Concentration in J1939. FMI 1 indicates a valid reading below the normal range. The International A26 uses Navistar's engine management system and is serviced using International's Diamond Logic diagnostic software or JPRO. When DEF quality falls below the calibrated minimum, the ECM activates the SCR inducement logic with the same progressive sequence used by other Class 8 platforms.

Common Symptoms

• Amber check engine or DEF warning lamp on the International instrument cluster
• DEF quality warning message on the International display
• Inducement distance counter in International service tools or telematics
• No immediate power loss at initial fault set

Possible Causes

Possible causes may include the items below. The list is not a parts diagnosis.

• DEF tank filled with water or wrong fluid
• DEF diluted by water ingestion through a leaking cap or tank
• DEF aged or heat-degraded below minimum concentration
• DEF quality sensor fault

First Checks

• Sample DEF from the tank and inspect for cloudiness or discoloration
• Connect International Diamond Logic or equivalent diagnostic tool and check active codes, DEF quality sensor live data, and inducement counter
• Inspect DEF filler cap and tank for damage or contamination
• Check sensor wiring if DEF quality is good but sensor still reads low
• Use ServiceMaxx to run the DEF supply pump commanded flow test
• Check for companion DEF level codes that may indicate a DEF module sensor group failure

Can I Keep Driving?

The A26 can continue operating in the initial warning stage, but the inducement timer is running. Resolve the DEF quality issue and reset the counter via International diagnostic tools before any extended runs.

Related Lookup Pages

• SPN 3364 topic page
• FMI 1 explanation
• Aftertreatment fault codes
• Search this code