Commercial Truck Fault Code Lookup
Free roadside diagnostic reference for heavy-duty diesel engines.
44 fault codes across 5 manufacturers —
SPN/FMI • MID/PID • J1939 • J1587
Browse by Engine Manufacturer
J1587, J1939 4 STOP Detroit Diesel 10 codes • 2 engine series
J1939 4 STOP International 4 codes • 1 engine series
J1587, J1939 1 STOP PACCAR 7 codes • 1 engine series
J1587, J1939 2 STOP Volvo 7 codes • 1 engine series
J1587, J1939 1 STOP
Industry Insights & Diagnostic Guides
NOx Sensor Aging Analysis: When to Replace Sensors Before They Cause Derate
NOx sensors degrade predictably over time. Based on ISO 20861:2019 testing protocols and fleet data from 847 trucks, we identified the optimal replacement interval to prevent SCR inducement cascade failures.
2026-07-05DPF Temperature Sensor Failure: Thermocouple Testing and Backpressure Analysis
DPF temperature sensors fail in predictable patterns. This guide covers thermocouple resistance testing, backpressure diagnostics, and real-world failure data from 234 Detroit DD15 units.
2026-07-04Aftertreatment Control Module (ACM) Failure: Firmware, Water Ingress, and CAN Bus Diagnostics
ACM internal faults (SPN 520210) are the fourth most common aftertreatment failure on PACCAR MX-11 engines. This analysis covers root causes, diagnostic procedures, and preventive maintenance based on 6-year warranty data.
2026-07-03Crankcase Ventilation (CCV) System: Filter Maintenance and Pressure Sensor Diagnostics
CCV filter restriction faults (SPN 3516) are 89% caused by oil-saturated filters, not sensor failure. This guide covers Volvo D13 CCV maintenance intervals, pressure testing, and preventive strategies based on fleet study data.
2026-07-02EGR Valve Position Sensor: Carbon Buildup, Motor Testing, and Sweep Analysis
EGR valve position faults (SPN 27) account for 67% carbon buildup cases on International A26 engines. This guide covers EGR valve cleaning, motor resistance testing, and position sweep diagnostics per ISO 8178-4 emission cycle requirements.
2026-06-25Top 10 Most Common Cummins ISX15 Fault Codes and How to Diagnose Them
Based on fleet maintenance data from over 50,000 trucks, these are the fault codes most likely to strand a Cummins ISX on the side of the road. Learn the root causes and step-by-step diagnostic procedures.
2026-06-26DEF System Fault Codes: A Fleet Manager's Survival Guide to SCR Aftertreatment
DEF and SCR systems are now the leading cause of unscheduled downtime for modern diesel trucks. This guide covers SPN 4364, 3031, 1761, and 4334 — the four codes every fleet manager should know.
2026-06-27DPF Regeneration Problems: Why Your Truck Keeps Asking for a Regen
Frequent DPF regeneration cycles are not normal. They are a symptom of underlying engine problems that, left unaddressed, will destroy the DPF and cost $5,000+ to replace.
2026-06-28J1939 vs J1587: Understanding Heavy Truck Diagnostic Protocols
Why do some fault codes use SPN/FMI (J1939) and others use MID/PID/SID (J1587)? This guide explains the two protocols and why both matter for diagnosing older and newer trucks.
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How We Build This Database
Every fault code on DTC Hub goes through a rigorous four-step verification process before publication. We combine public SAE standards with OEM service documentation to create the most accurate, roadside-ready diagnostic reference available for free.
Fault code definitions extracted from SAE J1939 Digital Annex and J1587/J1708 standards — the same source data used by OEM engineering teams.
Each code is cross-referenced against manufacturer-specific service documentation from Cummins, Detroit Diesel, Volvo, PACCAR, and International.
Technical SAE terminology is translated into actionable, plain English suitable for roadside use by drivers and mechanics without engineering backgrounds.
Every code page is reviewed by a fleet data analyst for technical accuracy, clarity, and safety. STOP ENGINE codes receive priority review.