SCR Conversion Efficiency Low (J1939)
The VOLVO-MACK-SPN4364-FMI18 (Volvo/Mack D/MP Series) diesel fault code means: SCR Conversion Efficiency Low (J1939). This is a serious severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- intermediate
- Estimated cost
- $400-$2,500
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Common Symptoms
- Check Engine Light illuminated
- Possible engine derate
- Warning message on driver display
- System-specific warning lamp (DPF/DEF/coolant/etc.)
Probable Causes (Ranked by Likelihood)
- DEF quality poor (contaminated, diluted, or old DEF) Very Likely
- DEF doser clogged with urea crystallization Likely
- SCR catalyst aged or thermally damaged Likely
- NOx sensor drift skewing efficiency calculation Possible
- Exhaust leak between DPF and SCR Possible
Step-by-Step Diagnostic Procedure
Connect Volvo PTT or Mack Guided Diagnostics and read inlet/outlet NOx and DEF dosing data.
Test DEF quality with a refractometer (must be exactly 32.5% urea).
Inspect DEF doser nozzle for urea crystallization; clean with distilled water.
Inspect exhaust between DPF and SCR for leaks or cracked pipes.
If DEF quality, doser, and exhaust are good, SCR catalyst replacement may be required.
After any replacement, run SCR self-test via Volvo PTT or Mack Guided Diagnostics.
Frequently Asked Questions
What does Volvo/Mack code SPN4364-FMI18 mean?
Volvo/Mack code SPN4364-FMI18 (SCR Conversion Efficiency Low (J1939)) is a serious-severity diagnostic trouble code set on D11/MP7, D13/MP8, and D16/MP10 diesel engines in Volvo VNL/VNR and Mack Anthem/Pinnacle/Granite/Titan trucks. It indicates a fault in the SCR / DEF system system and should be read with Volvo Premium Tech Tool (PTT) or Mack Guided Diagnostics.
Can I drive a Volvo or Mack truck with code SPN4364-FMI18?
Short distances may be acceptable to reach a repair facility, but the fault will escalate to derate (typically 55 mph then 5 mph on aftertreatment faults). Do not defer diagnosis beyond a shift.
How much does it cost to fix Volvo/Mack code SPN4364-FMI18?
Typical repair falls in the range $400-$2,500. Sensor/wiring repairs are at the low end; EGR cooler, NOx sensor set, DEF pump, injector, or head work runs at the high end. Volvo PTT or Mack Guided Diagnostics is normally required for calibration and parameter programming.
Sources
This page is built from documented references. Verify against your own service info before repair work.