SCR Conversion Efficiency Below Threshold
The DD-4364-17 (Detroit Diesel DD Series) diesel fault code means: SCR Conversion Efficiency Below Threshold. This is a serious severity code.
- Keep driving?
- No -- stop driving
- DIY difficulty
- advanced
- Estimated cost
- $1,200-$3,800
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Common Symptoms
- Check Engine Light / Amber Warning Lamp illuminated
- DEF warning lamp with countdown
- Engine derate (reduced torque / 5 mph limp)
- Aftertreatment warning
Probable Causes (Ranked by Likelihood)
- DEF dosing problem (clogged doser) Very Likely
- Low-quality or contaminated DEF Likely
- Failed SCR catalyst Possible
- NOx sensor mismatch Possible
- Exhaust leak between DPF and SCR Possible
Step-by-Step Diagnostic Procedure
Test DEF with a refractometer — must read 32.5%.
Perform SCR efficiency test through DDDL.
Remove and inspect DEF doser injector for spray pattern.
Smoke-test aftertreatment for leaks.
If catalyst is aged, replace SCR; thermal cleaning rarely restores it.
Frequently Asked Questions
What is Detroit Diesel fault code DD-4364-17?
Detroit Diesel fault DD-4364-17 (SPN 4364 FMI 17) indicates: SCR Conversion Efficiency Below Threshold. It is a serious-severity fault and is commonly seen on DD13/DD15/DD16 engines in Freightliner and Western Star chassis.
Can I drive my Freightliner or Western Star with fault DD-4364-17?
It depends on severity. Critical and serious faults trigger derate or engine shutdown — do not continue driving. Moderate faults usually allow continued operation short-term but schedule repair to prevent cascading aftertreatment damage.
How much does it cost to fix Detroit Diesel fault DD-4364-17?
Typical repair cost is $1,200-$3,800. Sensor/harness fixes fall at the low end; turbo actuator, injector, aftertreatment component, or head gasket repairs fall at the high end. Detroit DDDL software and sometimes factory parameter reset are required for proper reset.
Sources
This page is built from documented references. Verify against your own service info before repair work.