SPN 3364: DEF Quality and Communication Faults

What SPN 3364 identifies

SPN 3364 concerns DEF quality. The FMI determines whether the report concerns concentration or another failure mode. FC 3868 is 3364/FMI 9 in the cited guide: missing or irregular quality updates do not establish that the fluid is contaminated. Blue Bird SU2103 / Shaw 0000297252, revision B (2021)

Documented SPN/FMI examples

Scroll horizontally to see the application and source.

Examples only; a dash means no separate FC is supplied here. *See source applicability below; a model name alone does not establish calibration coverage.

Separate fluid quality from signal problems

1. Identify the header generation, part number and applicable engine fault procedure.
2. For FMI 9, use the communication branch: check the required supply, harness and sensor messages before making a fluid-quality judgment.
3. For a concentration complaint, obtain a representative tank sample and follow the OEM-approved fluid test. Compare the sample result with the reported reading.
4. If contamination or a component defect is established, follow the applicable cleaning or repair process and verify the result. A sensor replacement cannot establish that the remaining fluid is suitable.

The 31–34% refractometer band in the cited Detroit GHG14/GHG17 procedure applies to that service check. It is not a universal acceptance range for all DEF specifications. Detroit 01 13-16 (January 2016)

Frequently Asked Questions