Mack Fault Codes — Complete Guide

Mack SPN/FMI codes cover MP7, MP8, MP10. This hub lists 41 diagnostic pages with symptoms, ranked causes, scan-tool steps, and 2026 repair costs — use INSITE, DiagnosticLink, or EST depending on your engine family.

By Professional Diesel Repair TeamPublished: January 2026Last updated: September 2026

How We Tested and Verified

Mack fault code definitions cross-checked against SAE J1939-71 and Mack OEM service bulletins. Diagnostic tips validated by field technicians September 2026.

Mack Engine Platforms

Mack engines covered on this site include: MP7, MP8, MP10. Diagnostic procedures vary by platform — always verify against your specific engine serial number and calibration.

Most Common Mack Fault Codes

Code	Component	Severity	Definition
SPN 1569 FMI 31	Engine Protection Torque Derate	Critical	Engine Protection System - Torque Derate - Condition Exists
SPN 190 FMI 0	Engine Speed Sensor Circuit	Critical	Engine Speed - Data Valid But Above Normal Operational Range
SPN 3226 FMI 0	Outlet NOx Sensor	Critical	Aftertreatment 1 SCR Outlet NOx Sensor - Data Valid But Above Normal Operating Range - Most Severe Level
SPN 3480 FMI 16	HC Doser Fuel Supply Pressure	Critical	Aftertreatment 1 Hydrocarbon Doser Fuel Supply Pressure - Data Valid But Above Normal Operating Range
SPN 5246 FMI 0	SCR Operator Inducement	Critical	Regulatory Derate - Most Severe Level Active
SPN MP8-DERATE FMI N/A	Mack MP8 Aftertreatment Derate System	High	Aftertreatment derate stages, inducement timers, and common fault chains on Mack MP8 engines using Mack PTT
SPN 100 FMI 18	Engine Oil Pressure Sensor / Oil Pressure Circuit	High	Engine Oil Pressure - Data Valid But Below Normal Operating Range - Moderately Severe Level
SPN 105 FMI 16	Intake Manifold 1 Temperature Sensor (IMT)	High	Intake Manifold 1 Temperature - Data Valid But Above Normal Operating Range - Moderately Severe Level
SPN 1127 FMI 18	Turbocharger 1 Boost Pressure	High	Engine Turbocharger 1 Boost Pressure - Data Valid But Below Normal Operational Range - Moderately Severe Level
SPN 168 FMI 1	Battery / Charging System Circuit	High	Electrical Potential (Voltage) - Data Valid But Below Normal Operating Range
SPN 175 FMI 16	Engine Oil Temperature 1	High	Engine oil temperature moderately above normal operating range — a warning-level high oil temperature that precedes a more severe shutdown fault.
SPN 190 FMI 8	Engine Speed Sensor (Crankshaft)	High	Engine Speed - Abnormal Frequency, Pulse Width, or Period
SPN 3216 FMI 0	SCR Intake NOx Sensor	High	Aftertreatment SCR Intake NOx Sensor - Data Valid But High
SPN 3246 FMI 16	DPF Outlet Gas Temperature	High	Aftertreatment 1 Diesel Particulate Filter Outlet Gas Temperature - Data Valid But Above Normal Operating Range (FMI 16)
SPN 3363 FMI 16	DEF Pump Pressure	High	Aftertreatment 1 DEF Pump Pressure - Data Valid But Above Normal Operational Range - Moderately Severe Level
SPN 3364 FMI 9	DEF Quality	High	Aftertreatment DEF Quality - Abnormal Update Rate
SPN 3509 FMI 4	Sensor Supply Voltage 1	High	Sensor Supply Voltage 1 - Voltage Below Normal, Or Shorted To Low Source
SPN 3719 FMI 16	DPF Ash Load	High	Aftertreatment Diesel Particulate Filter Ash Load - Data Valid But Above Normal Operating Range
SPN 4363 FMI 1	SCR Outlet Gas Temperature Sensor	High	SCR outlet gas temperature reading is below normal operating range during active regeneration — FMI 1 indicating sensor failure, exhaust leak, or impaired regen process
SPN 4364 FMI 18	SCR NOx Efficiency	High	Aftertreatment SCR NOx Conversion Efficiency - Data Valid But Below Normal

Mack-Specific Diagnostic Tips

Mack uses Volvo-based aftertreatment on MP8 — cross-reference Volvo D13 diagnostic trees.
MP7 turbo actuator harness chafes against frame rail; inspect before condemning actuator.
GuardDog Connect remote diagnostics can pre-stage fault data before the truck arrives.