Peterbilt Fault Codes — Complete Guide

Peterbilt SPN/FMI codes cover 579 MX-13, 389 Cummins X15. This hub lists 24 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

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

Peterbilt Engine Platforms

Peterbilt engines covered on this site include: 579 MX-13, 389 Cummins X15. Diagnostic procedures vary by platform — always verify against your specific engine serial number and calibration.

Most Common Peterbilt Fault Codes

Code	Component	Severity	Definition
SPN 100 FMI 1	Engine Oil Pressure Sensor / Oil Pressure Circuit	Critical	Engine Oil Pressure - Data Valid But Below Normal Operating Range - Moderately 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 0	Fuel Rail Pressure	Critical	Engine Fuel 1 Injector Metering Rail 1 Pressure — Data Valid But Above Normal Operating Range - Most Severe Level
SPN 653 FMI 7	Injector Cylinder 3	Critical	Injector Cylinder 3 - Mechanical System Not Responding
SPN 579-DEF FMI N/A	Peterbilt 579 DEF Quality System	High	DEF quality fault diagnosis on Peterbilt 579 trucks — SPN 3364, SPN 4334, refractometer testing, and tank drain procedures across Cummins and PACCAR power
SPN 102 FMI 16	Boost Pressure Sensor / Overboost Condition	High	Intake Manifold 1 Pressure - Data Valid But Above Normal Operating Range - Moderately Severe Level
SPN 1231 FMI 9	J1939 Network #2 (Secondary CAN Bus)	High	J1939 Network #2 abnormal update rate — the secondary CAN bus is not delivering messages at the expected frequency.
SPN 1381 FMI 1	Fuel Supply Pump Inlet Pressure	High	Engine Fuel Supply Pump Inlet Pressure - Data Valid But Below Normal Operational Range - Most Severe Level
SPN 175 FMI 1	Engine Oil Temperature Sensor	High	Engine Oil Temperature 1 - Data Valid But Below Normal Operating Range
SPN 3364 FMI 9	DEF Quality Sensor	High	Aftertreatment 1 DEF Tank - Liquid Quality Parameter - Abnormal Update Rate
SPN 3609 FMI 3	DPF Intake Pressure Sensor	High	DPF intake pressure sensor signal voltage is above normal operating range — FMI 3 high-voltage fault indicating a short to supply voltage or open sensor ground
SPN 4094 FMI 16	DPF Soot Load Sensor/Model	High	Aftertreatment 1 Diesel Particulate Filter Soot Load Percent - Data Valid But Above Normal Operating Range - Moderately Severe Level
SPN 412 FMI 5	Turbocharger Boost Control	High	Turbocharger Boost Control - Current Below Normal Or Open Circuit
SPN 4364 FMI 3	SCR NOx Conversion Efficiency	High	Aftertreatment 1 SCR Catalyst NOx Conversion Efficiency - Voltage Above Normal
SPN 100 FMI 18	Engine Oil Pressure	Medium	Engine Oil Pressure — Data Valid But Below Normal Operating Range - Moderately Severe
SPN 105 FMI 3	Intake Manifold Temperature	Medium	Engine Intake Manifold 1 Temperature — Voltage Above Normal or Shorted to High Source
SPN 110 FMI 9	Engine Coolant Temperature	Medium	Engine Coolant Temperature 1 — Abnormal Update Rate
SPN 1127 FMI 16	Turbocharger 1 Boost Pressure	Medium	Engine Turbocharger 1 Boost Pressure - Data Valid But Above Normal Operational Range - Moderately Severe Level
SPN 1188 FMI 3	Wastegate Actuator Position Sensor	Medium	Wastegate Actuator Position - Voltage Above Normal or Shorted to High Source
SPN 132 FMI 2	Engine Inlet Air Mass Flow Rate Sensor	Medium	Engine Inlet Air Mass Flow Rate - Erratic, Intermittent, or Incorrect

Peterbilt-Specific Diagnostic Tips

Peterbilt 579 aftertreatment layout differs from Kenworth T680 — doser location is aft of turbo.
Check PACCAR gateway module firmware when multiple SPN communication faults stack.
389 long-hood trucks with Cummins X15 need 15W-40 CK-4 oil — wrong viscosity triggers SPN 100.