SPN 4364 FMI 18: SCR Efficiency Diagnosis

What SPN 4364 identifies

SPN 4364 concerns SCR conversion efficiency. It describes monitored system performance. It does not identify a replacement part. The documented example below is Detroit DD GHG14/GHG17 FMI 18; use the engine's current procedure for the actual calibration. Detroit 01 13-16 (January 2016)

Documented SPN/FMI example

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.

Check the inputs before condemning the catalyst

1. Record all faults and inspect the source procedure's prerequisite checks. Address related sensor faults before drawing conclusions from conversion data.
2. Evaluate DEF condition, dosing and NOx readings with the OEM service routine. Test conditions and pass/fail limits belong to that routine.
3. Evaluate exhaust condition and the remaining system components using the procedure's decision points. The conversion fault alone is insufficient evidence for replacing the SCR assembly.
4. Verify the repair under the required conditions and record whether derate or inducement faults remain.

The cited Detroit bulletin uses a 31–34% refractometer band and a 108–132 mL dosing test. Those values describe that procedure; they are not presented here as universal DEF product or flow specifications. Detroit 01 13-16 (January 2016)

Frequently Asked Questions