PACCAR Fault Codes — Complete Guide

PACCAR SPN/FMI codes cover MX-11, MX-13, PX-7 and 1 more platforms. This hub lists 40 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

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

PACCAR Engine Platforms

PACCAR engines covered on this site include: MX-11, MX-13, PX-7, PX-9. Diagnostic procedures vary by platform — always verify against your specific engine serial number and calibration.

Most Common PACCAR Fault Codes

Code	Component	Severity	Definition
SPN 100 FMI 1	Engine Oil Pressure Sensor	Critical	Engine Oil Pressure - Data Valid But Below Normal Operating Range - Most Severe Level
SPN 111 FMI 1	Engine Coolant Level Sensor	Critical	Engine Coolant Level - Data Valid But Below Normal Operating Range - Most Severe Level
SPN 157 FMI 1	Fuel Rail Pressure Sensor	Critical	Engine Injector Metering Rail 1 Pressure - Data Valid But Below Normal Operational Range - Most Severe Level
SPN 190 FMI 0	Engine Speed Sensor Circuit	Critical	Engine Speed - Data Valid But Above Normal Operational Range
SPN 5246 FMI 16	SCR System	Critical	SCR System Fault - Diesel Exhaust Fluid Quality
SPN MX-13-SCR FMI N/A	PACCAR MX-13 SCR Inducement System	High	SCR inducement stage patterns and common fault chains on PACCAR MX-13 engines diagnosed with Davie4 and JPRO
SPN 1209 FMI 16	Engine Exhaust Gas Pressure	High	Engine Exhaust Gas Pressure - Data Valid But Above Normal Operating Range (FMI 16)
SPN 1231 FMI 4	Fuel Rail Pressure	High	Fuel Rail Pressure - Voltage Below Normal, Or Shorted To Low Source
SPN 164 FMI 1	Fuel Rail Pressure	High	Fuel Rail Pressure - Data Valid But Below Normal Operating Range
SPN 168 FMI 1	Battery / Charging System Circuit	High	Electrical Potential (Voltage) - Data Valid But Below Normal Operating Range
SPN 27 FMI 3	EGR Valve Position Sensor	High	EGR valve position sensor signal voltage is above normal — FMI 3 high-voltage fault on the MX-13 or MX-11 EGR actuator position feedback circuit
SPN 3216 FMI 0	SCR Intake NOx Sensor	High	Aftertreatment SCR Intake NOx Sensor - Data Valid But High
SPN 3226 FMI 0	SCR Outlet NOx Sensor	High	Aftertreatment SCR Outlet NOx Sensor - Data Valid But High
SPN 3242 FMI 16	DPF Intake Gas Temperature Sensor	High	Aftertreatment 1 Diesel Particulate Filter Intake Gas Temperature - Data Valid But Above Normal Operational Range - Moderately Severe Level
SPN 3364 FMI 9	DEF Quality	High	Aftertreatment DEF Quality - Abnormal Update Rate
SPN 3510 FMI 3	5-Volt Sensor Supply Voltage 2	High	Sensor Supply Voltage 2 - Voltage Above Normal, or Shorted to High Source
SPN 3609 FMI 16	DPF Intake Pressure Sensor	High	Aftertreatment 1 Diesel Particulate Filter Intake Pressure - Data Valid But Above Normal Operating Range
SPN 3719 FMI 16	DPF Ash Load	High	Aftertreatment Diesel Particulate Filter Ash Load - Data Valid But Above Normal Operating Range
SPN 3936 FMI 0	SCR Conversion Efficiency (NOx Sensors)	High	Aftertreatment 1 SCR Conversion Efficiency - Data Valid But Above Normal Operating Range - Most Severe Level
SPN 4364 FMI 18	SCR NOx Efficiency	High	Aftertreatment SCR NOx Conversion Efficiency - Data Valid But Below Normal

PACCAR-Specific Diagnostic Tips

PACCAR EST (Electronic Service Tool) required for SCR efficiency tests.
MX-13 EGR valve carbon packing causes repeated SPN 2631 codes in stop-go duty cycles.
Verify DEF tank heater operation before winter NOx efficiency faults.