SPN/FMI Hub
Read SPN/FMI codes, distinguish DEF level from NOx, and choose documented examples by engine. Bilingual guides with OEM scope and sources.
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Diesel Diagnostic
Knowledge Base
Expert guides, fault code references, and troubleshooting resources built by real technicians for independent shops and fleets.
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Technical articles. Common causes. Expert advice.
DPF pressure: guides by engine
Guides with codes, documented applications and information to prepare for diagnosis. Choose your engine brand.
CUMMINS
Cummins ISX15/X15: DPF pressure and fault codes 1921/1922
What FC 1921, 1922 and SPN 3251 indicate on Cummins engines. Distinguish DPF pressure, electrical faults and the manufacturer-documented X15 case.
DETROIT
Detroit DD13/DD15/DD16: SPN 3251 and DPF pressure
Detroit SPN 3251 FMI 0, 16, 2 and 20: EPA10, GHG14 and GHG17 differences, DOC/DPF pressure and information to save before diagnosis.
PACCAR
PACCAR MX-13: DPF pressure, P3762, P3770 and P3794
P3762, P3770 and P3794 on the PACCAR MX-13 EPA2013: electrical signals, outlet pressure and DPF differential pressure. What to check before applying them to an MX-11.
Fault Code Library
Technician guides for the SPNs shops actually see. Call (800) 697-7626 for a remote session.
SPN 3226
Outlet NOx SPN 3226: documented Cummins fault-code mappings, Detroit EPA10/GHG14 drift diagnosis, and Navistar water-intrusion applicability.
Open →SPN 1761
DEF level SPN 1761: sourced FC 1673, 3497, 4677 and 4769 examples. Distinguish low fluid from communication or sensor faults.
Open →SPN 3216
SPN 3216 identifies inlet NOx. Sourced 2013 Cummins code examples and a diagnostic approach that separates signal faults from SCR efficiency.
Open →SPN 4364
Detroit GHG14/GHG17 SPN 4364 FMI 18: documented scope, DEF and NOx checks, and why the code does not identify a failed catalyst by itself.
Open →SPN 1569
SPN 1569 FMI 31 and Cummins FC 3714: a documented torque-derate indication. Find the associated faults and verify the underlying repair.
Open →SPN 5246
SPN 5246 reports SCR inducement severity. Documented Navistar FMI 15, 16 and 0 examples, with engine scope and calibration limits.
Open →SPN 3364
SPN 3364 and Cummins FC 3868: distinguish concentration faults from FMI 9 communication faults using documented Shaw/Cummins examples.
Open →SPN 3251
SPN 3251 pressure codes: documented Cummins differential-pressure examples and Detroit outlet-pressure diagnostics, with scope and sources.
Open →SPN 4374
Detroit GHG14 SPN 4374: sourced FMI 0, 3 and 4 examples. Understand pump speed versus delivered pressure before replacing the pump.
Open →SPN 641
SPN 641: sourced Cummins VGT fault codes and Navistar A26 examples. Detroit turbo hardware and wastegate diagnostics require separate applicability checks.
Open →FMI 0–31
Common FMI meanings, OEM examples and SAE revision limits. Values 22–30 require the applicable standards edition.
Open →Diagnostics & Fault Codes
Complete Guide to Diesel Fault Codes: SPN/FMI Explained
Read SPN/FMI codes, distinguish DEF level from NOx, and choose documented examples by engine. Bilingual guides with OEM scope and sources.
Read ArticleHow to Read Truck Fault Codes with NEXIQ USB-Link 3
Connect the correct NEXIQ model and vehicle cable, select a supported diagnostic application, and save complete controller-specific fault information.
Read ArticleTruck ECM, ACM, CPC and TCM: Controller Roles
A heavy-duty truck uses communicating controllers. The engine ECM is not a universal master that directly controls every electronic module.
Read ArticleTruck Derate After Repair: Verification Before Reset
A cleared code is not proof of a repaired truck. Confirm the original fault, completed repair and OEM-required verification before a derate reset.
Read ArticleAftertreatment Derate and Inducement: OEM-Specific Stages
Torque reduction and speed restriction vary by engine and calibration; there is no single 55/35/5-mph ladder for every truck.
Read ArticleEngine diagnostic guides
Cummins Aftertreatment Troubleshooting by Engine
Use the engine serial number, complete fault list and documented tests to investigate Cummins DEF, NOx, DPF and SCR problems.
Read ArticleDetroit DD13 and DD15 Diagnostics: Identify the Generation
Match Detroit turbo, module and aftertreatment diagnosis to the engine generation rather than applying one DD-platform procedure to every truck.
Read ArticlePACCAR MX-13 Diagnostics: Software, Faults and Evidence
Identify the engine and controller before choosing PACCAR software or applying an aftertreatment troubleshooting procedure.
Read ArticleFinding Truck Sensors and Modules by Exact Application
Find ECMs, NOx sensors and aftertreatment components using the vehicle and engine configuration, not a universal model-name location chart.
Read ArticleTools & Equipment
Diesel Diagnostic Tools: A Practical Starting Checklist
Build a heavy-duty diagnostic setup around supported tasks, verified software access and a compatible vehicle interface.
Read ArticleChoosing a Diesel Diagnostic Laptop and NEXIQ Package
Choose a diagnostic laptop by its actual configuration, software requirements, interface and support terms—not the model name alone.
Read ArticleHeavy-Duty Diagnostic Adapters: Compare by Task
Evaluate an adapter by vehicle network, software support, cables, programming requirements and lifecycle rather than blanket brand claims.
Read ArticleNEXIQ vs Noregon: Compare Model, Coverage and Support
Compare specific adapter models and software requirements; a brand-level ranking cannot establish compatibility for your truck or programming job.
Read ArticleMaintenance & Compliance
DPF Regeneration: Types, Preconditions and Diagnosis
Understand passive, active and parked DPF regeneration, and why soot readings and test conditions must be interpreted for the actual engine.
Read ArticleFleet Diagnostic Maintenance: A Record-Based Checklist
Use vehicle-specific schedules and a consistent diagnostic record to plan heavy-duty fleet maintenance and investigate repeated faults.
Read ArticleClean Truck Check: Requirements and CARB References
Check vehicle eligibility, registration and CTC-VIS deadlines against current CARB guidance before scheduling heavy-duty emissions testing.
Read ArticleGetting Started
Remote Diesel Diagnostics: Equipment and Session Process
Remote truck diagnostics requires a compatible interface and laptop at the vehicle, appropriate software access and someone available for physical checks.
Read ArticleDiesel ECM Programming, Calibration and Reflashing
Understand the difference between a software update, parameter change and replacement-module setup before requesting truck ECM programming.
Read ArticleOBD-II and Heavy-Duty Truck Diagnostics: Coverage Limits
An OBD-II connector does not establish full vehicle coverage. Match the protocol, controller, software and intended task before selecting equipment.
Read ArticleReady to Level Up?
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