International SPN 4358 FMI 14: SCR Catalyst Exhaust Differential Pressure Special Instructions
SPN 4358 FMI 14 (FMI 14) — Aftertreatment 1 SCR Catalyst Exhaust Gas Differential Pressure - Special Instructions
Quick Answer
SPN 4358 FMI 14 on International requires special instruction diagnosis for SCR differential pressure — inspect sense lines and manometer-test before replacing the catalyst.
Overview: International SPN 4358 FMI 14
SCR differential pressure tells the International ECM whether exhaust flow through the catalyst is normal. FMI 14 means the diagnosis is not complete until you follow the OEM procedure for line inspection, sensor cross-check, and restriction verification. ProfessionalDieselRepair.com treats plugged sense tubes as the default cause until manometer data proves otherwise.
Repair Snapshot
Time
1.5 - 5 Hours
Difficulty
Advanced
Parts Cost
$60 - $3,200
Dealer Labor
$850+
Tools Required
- ServiceMaxx
- Noregon JPRO
- Exhaust Manometer
- Jaltest
What SPN 4358 FMI 14 Means
SPN 4358 FMI 14 on International LT/RH series with N13/N9 engines requires OEM special instructions for SCR catalyst differential pressure diagnosis. The fault covers sensor validation, sense line inspection, and catalyst restriction testing before SCR replacement.
Symptoms Drivers Notice
- Aftertreatment warning lamp with SPN 4358 FMI 14
- SCR differential pressure reading stuck or implausible on ServiceMaxx
- Gradual power loss if restriction is genuine
- Possible companion DPF or DOC pressure codes
- Inducement countdown on some calibrations if unresolved
Most Likely Root Causes
Plugged SCR differential pressure sense lines
CommonSoot and condensation block narrow sample tubes, producing false high differential pressure readings.
Failed SCR differential pressure sensor
OccasionalSensor drift or internal diaphragm damage reports incorrect pressure after sense lines test clean.
Ash or soot loading restricting SCR substrate
OccasionalGenuine catalyst restriction raises differential pressure under load when sense lines are clear.
Damaged catalyst from prior thermal event
RareMelted or collapsed substrate creates permanent high backpressure confirmed by direct measurement.
Common Misdiagnoses (Don't Waste Parts)
Ordering SCR catalyst before sense line inspection
Why it happens: High differential pressure sounds like a restricted brick.
Do this instead: Follow FMI 14 special instructions — clear tubes and manometer-test first; a parts-cannon catalyst on a plugged hose is an expensive misdiagnosis.
Replacing sensor without confirming actual exhaust delta-P
Why it happens: Sensor is named in SPN 4358.
Do this instead: Tee a manometer into sense ports — if mechanical reading is normal, fix wiring or ECM; if high, investigate restriction.
Ignoring companion DPF codes
Why it happens: SCR and DPF faults are treated as separate systems.
Do this instead: Upstream DPF restriction can elevate SCR differential pressure — diagnose exhaust path holistically.
Master Tech Commentary
Mechanic's Notes
ProfessionalDieselRepair.com clears SCR sense tubes before any catalyst quote on International SPN 4358 FMI 14. FMI 14 includes manometer cross-check steps — a plugged sample line and a melted brick look identical on the dash, and only one of them needs a five-figure aftertreatment module. Skipping the procedure is parts-cannon at fleet scale.
Step-by-Step Diagnostic Procedure
- Step 1: Connect ServiceMaxx or Noregon JPRO and open SPN 4358 special instruction workflow for International aftertreatment.
- Step 2: Inspect SCR differential pressure sense lines at both catalyst ports for soot, kinks, or moisture plugs.
- Step 3: Compare scan tool differential pressure to a manual manometer tee'd into sense ports.
- Step 4: Run idle and loaded pressure profiles — flat high reading with clear lines suggests sensor fault; rising pressure with load suggests restriction.
- Step 5: Clear sense lines or replace sensor per special instructions before authorizing SCR catalyst replacement.
Professional service / OEM-level scan tools are recommended before clearing this fault for good.
Live Data & Freeze-Frame Tips
In ServiceMaxx, log SCR differential pressure at idle, 1200 RPM, and under load. A plugged sense line often shows a fixed high value regardless of RPM; genuine restriction climbs proportionally with exhaust flow.
Safety Warnings
- Allow SCR housing to cool before disconnecting pressure sense fittings.
- Wear heat-resistant gloves when working under the aftertreatment module.
- Relieve residual pressure in sense lines slowly when disconnecting.
When to Limp In vs Tow
Tow if inducement derate is active or if backpressure-related power loss makes highway operation unsafe.
Prevention Tips for Fleets & Owner-Operators
- Blow out SCR sense lines during scheduled aftertreatment PM.
- Use approved DEF to limit ash accumulation in the catalyst.
- Address DPF restriction before SCR pressure climbs.
- Keep manometer test ports capped and free of debris after service.
Related Fault Codes
SPN 3251 FMI 14
DPF differential pressure special instructions upstream of SCR.
SPN 4360 FMI 14
SCR intake temperature special instructions on the same aftertreatment module.
SPN 5246 FMI 7
SCR inducement severity when efficiency faults follow unresolved pressure issues.
Frequently Asked Questions
What does International SPN 4358 FMI 14 mean?
SCR catalyst differential pressure fault requiring OEM special instruction diagnosis beyond generic FMI definitions.
Can plugged sense lines cause this code?
Yes — blocked sample tubes are the most common root cause on International aftertreatment.
Which tools diagnose SPN 4358 FMI 14?
ServiceMaxx, Noregon JPRO, and Jaltest all read SCR differential pressure and special instruction text.
Does this code trigger derate immediately?
Depends on calibration — some versions start inducement countdown while others warn first.
How much does SCR replacement cost if restriction is real?
SCR catalyst or one-box replacement is among the highest aftertreatment repairs — often several thousand dollars.
Can I clear SPN 4358 without fixing the cause?
The fault returns on the next drive cycle if sense lines, sensor, or restriction remain unresolved.
More International codes on this system
- International SPN 3364 FMI 9 — DEF Quality Sensor
- International SPN 4094 FMI 16 — DPF Soot Load
- International SPN 4363 FMI 3 — Aftertreatment #1 SCR Catalyst Outlet Gas Temperature Sensor
- International SPN 4364 FMI 15 — SCR NOx Conversion Efficiency Monitor
- International SPN 4094 FMI 3 — DPF Soot Load Percent Sensor
- International SPN 3719 FMI 16 — DPF Ash Load
- International SPN 4364 FMI 18 — SCR NOx Efficiency
- International SPN 3216 FMI 0 — SCR Intake NOx Sensor
Guides that go deeper
- Detroit DDDL Basics: Finding the Root Code Behind a Derate
Use Detroit DDDL the right way: separate root SPN/FMI faults from inducement result codes, read derate stage data, and stop replacing parts on guesses.
- SPN 4364 SCR Efficiency Low: Fix Order That Saves Money
A money-saving fix order for SPN 4364 SCR efficiency low—DEF quality, dosing, NOx sensor trust, then catalyst—so you stop buying the brick first.
- DEF in the Diesel Tank (or Diesel in the DEF Tank): Damage Control Steps
Do not start the engine. DEF is 32.5% urea in water and corrodes fuel system metals; diesel destroys SCR catalyst coating and doser seals. Cranking converts a drain-and-flush job into a fuel system or aftertreatment replacement.