Detailed guide for SPN 4364 FMI 18
Back to top ↑SCR efficiency faults trigger the countdown because emissions control is not meeting targets.\n\nRule out DEF quality, dosing, leaks, and sensor accuracy first.
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Share ↓SPN 4364 FMI 18Severity: CriticalPACCAR • PACCAR MX-13
SPN 4364 FMI 18: SCR conversion efficiency below normal (inducement risk)
Quick Answer
When SPN 4364 FMI 18 sets, the ECM is reporting an aftertreatment or emissions-system fault associated with the component named in this code.
SCR, NOx, temperature, pressure, catalyst, heater, wiring, and DEF-delivery faults use different diagnostic strategies, so diagnose the specific component rather than assuming a dosing problem.
Code
SPN 4364 FMI 18
Severity
Critical
Applies to
PACCAR • PACCAR MX-13
Can I drive?
Avoid unnecessary driving until SPN 4364 FMI 18 is diagnosed. A critical fault can affect engine protection, emissions operation, or drivability depending on the OEM calibration and companion codes. Confirm whether the fault is ACTIVE and check for stop-engine, derate, or inducement warnings.
Common Symptoms
- Aftertreatment warning
- Inducement/derate risk
- Poor NOx conversion
Likely Causes
- DEF dosing issue
- NOx sensor drift/fault
- Exhaust leak or SCR catalyst aging
Quick Diagnostic Checks
Check first- 1Scan for companion codes and record freeze-frame data (if available).
- 2Inspect connectors, harness rub points, and pins for corrosion.
- 3Check for other active faults that may be upstream causes (communications, sensors, air/fuel issues).
- 4After repair, clear codes and confirm the fault stays inactive after a drive cycle.
Common Fixes
- Verify DEF quality and dosing operation
- Check NOx sensor plausibility
- Inspect exhaust joints for leaks before blaming catalyst
Full technical sections↓
What does SPN 4364 FMI 18 mean?
Back to top ↑When SPN 4364 FMI 18 sets, the ECM is reporting an aftertreatment or emissions-system fault associated with the component named in this code.
SCR, NOx, temperature, pressure, catalyst, heater, wiring, and DEF-delivery faults use different diagnostic strategies, so diagnose the specific component rather than assuming a dosing problem.
This page includes information for PACCAR / PACCAR MX-13 when available.
Confirm whether the fault is ACTIVE and review companion codes and live data before replacing parts.
How this system works (why SPN 4364 FMI 18 happens)
Back to top ↑Modern aftertreatment systems use temperature sensors, NOx sensors, pressure sensors, heaters, catalysts, DEF equipment, and model-based ECM checks together.
The ECM compares sensor signals and expected system behavior. A fault can therefore be electrical, sensor-related, catalyst-related, mechanical, or caused by another upstream condition.
The diagnostic path should follow the component named by the code instead of assuming every SCR or NOx fault is a DEF dosing problem.
Location hint for SPN 4364 FMI 18
Back to top ↑Component location varies by OEM and chassis. Use your engine’s service manual to confirm the sensor/valve location before replacing parts.
Tip: Inspect connectors and harness routing before replacing parts.
Scan tool checks for SPN 4364 FMI 18
Back to top ↑- Confirm whether SPN 4364 FMI 18 is ACTIVE and review freeze-frame data when available.
- Record companion aftertreatment, NOx, temperature, pressure, heater, DEF, or inducement faults.
- Use PACCAR DAVIE4 to review live data for the specific component named by this fault.
- Check signal plausibility, wiring, connector condition, and related sensor values before replacing parts.
If your tool can’t run actuator tests, you can still diagnose a lot with careful inspection + repeatability testing.
Step-by-step diagnostic for SPN 4364 FMI 18
Back to top ↑- Visual inspection (fast wins). Harness routing, connector pins, hoses/lines (if applicable), and obvious damage.
- Check fluid sanity. Not applicable unless your fault is fluid-related. Focus on inspections + repeatability.
- Confirm the fault is ACTIVE. Stored-only faults can be old events.
- Review component live data. Use PACCAR DAVIE4 or a capable heavy-duty scan tool to review the sensor or component data named by the fault and compare it with related aftertreatment readings.
- Verify after repair. Clear codes, road test, confirm it stays inactive.
Decision guide (fast path) for SPN 4364 FMI 18
Back to top ↑- If the fault is STORED only → inspect the named component and wiring, clear it, and monitor for recurrence.
- If ACTIVE → compare the relevant sensor or component live data with companion readings and operating conditions.
- If the signal is implausible → inspect wiring, connector pins, supply/ground, and the component itself.
- If multiple aftertreatment codes are active → diagnose the earliest or most upstream fault first.
Common misdiagnosis mistakes for SPN 4364 FMI 18
Back to top ↑- Treating every SCR, NOx, or aftertreatment fault as a DEF dosing problem.
- Replacing a sensor without checking its wiring, connector, supply voltage, and companion faults first.
- Ignoring other active emissions faults that may explain why this code set.
Will SPN 4364 FMI 18 cause derate or inducement?
Back to top ↑Critical aftertreatment faults can trigger rapid derate or inducement depending on OEM calibration and companion faults.
Exact behavior depends on ECM calibration and which companion faults are active.
“Do this first” checklist for SPN 4364 FMI 18
Back to top ↑- Scan for companion codes and record freeze-frame data (if available).
- Inspect connectors, harness rub points, and pins for corrosion.
- Check for other active faults that may be upstream causes (communications, sensors, air/fuel issues).
- After repair, clear codes and confirm the fault stays inactive after a drive cycle.
Tools needed to diagnose SPN 4364 FMI 18
Back to top ↑- Basic hand tools + good lighting for inspection
- Multimeter for connector/power/ground checks (if wiring suspected)
- PACCAR DAVIE4 (or equivalent scan tool) for live data and supported diagnostic tests
Prevention tips to avoid repeat SPN 4364 FMI 18
Back to top ↑- Fix small wiring/connector issues early before they become repeat faults.
- During service, inspect harness routing and clamp points near heat/vibration.
- Don’t ignore intermittent faults. “Erratic” usually gets worse.
What to check first for SPN 4364 FMI 18
- Inspect connectors and harness near the affected component for corrosion, rubbing, or loose pins.
- Check for upstream causes (communications, sensors, air/fuel issues).
- Check for other active faults that may be upstream causes (communications, sensors, air/fuel issues).
If the fault repeats after clearing, diagnose it as ACTIVE and review companion codes and live data before replacing parts.
Video walkthrough for SPN 4364 FMI 18
The videos below are embedded using YouTube’s official player. We do not host or claim ownership of this content. Use it as a visual reference and always confirm with diagnostics for your exact truck configuration.
SPN 4364 FMI 18, Def doser valve, failed regen
Channel: muhas1234 • View in BigRigFaults Media • YouTube source
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Ask the Community →Related fault codes for PACCAR PACCAR MX-13
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