Mercedes-Benz Fault Codes — Complete Guide

Mercedes-Benz SPN/FMI codes cover OM471, OM936. This hub lists 25 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

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

Mercedes-Benz Engine Platforms

Mercedes-Benz engines covered on this site include: OM471, OM936. Diagnostic procedures vary by platform — always verify against your specific engine serial number and calibration.

Most Common Mercedes-Benz 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 190 FMI 0	Engine Speed Sensor Circuit	Critical	Engine Speed - Data Valid But Above Normal Operational Range
SPN 3226 FMI 3	Outlet NOx Sensor	Critical	Aftertreatment 1 Outlet NOx Sensor - Voltage Above Normal (FMI 3)
SPN 524287 FMI 14	Aftertreatment Diesel Particulate Filter	Critical	DPF System - Special Instruction
SPN 5246 FMI 31	SCR Operator Inducement	Critical	Aftertreatment 1 SCR Operator Inducement - Severe Level
SPN 110 FMI 16	Engine Coolant Temperature Sensor	High	Engine Coolant Temperature - Data Valid But Above Normal Operating Range - Moderately Severe Level
SPN 157 FMI 16	Fuel Rail Pressure Sensor	High	Engine Injector Metering Rail 1 Pressure - Data Valid But Above Normal Operational Range - Moderately Severe Level
SPN 157 FMI 3	Injector Metering Rail 1 Pressure Sensor Circuit	High	Injector Metering Rail 1 Pressure - Voltage Above Normal, or Shorted to High Source
SPN 168 FMI 4	Battery / Charging System Circuit	High	Electrical Potential (Voltage) - Voltage Below Normal, Circuit Shorted Low
SPN 3251 FMI 0	DPF Differential Pressure Sensor	High	Aftertreatment 1 Diesel Particulate Filter Differential Pressure - Data Valid But Above Normal Operating Range - Most Severe Level
SPN 3364 FMI 9	DEF Quality Sensor	High	Aftertreatment 1 DEF Tank - Liquid Quality Parameter - Abnormal Update Rate
SPN 3509 FMI 3	Sensor Supply Voltage 1 (5V Reference)	High	5V sensor reference supply voltage above normal — the ECU's 5V reference rail powering multiple sensors is reading above its calibrated upper threshold.
SPN 4360 FMI 16	SCR Intake Gas Temperature	High	Aftertreatment 1 SCR Catalyst Intake Gas Temperature - Data Valid But Above Normal Operational Range - Moderately Severe Level
SPN 513 FMI 16	Actual Engine Percent Torque	High	Actual Engine Percent Torque - Data Valid But Above Normal Range
SPN 636 FMI 2	Crankshaft Position Sensor	High	Engine Position Sensor - Data Erratic, Intermittent, or Incorrect
SPN 651 FMI 6	Injector Cylinder #1	High	Engine Injector Cylinder #01 - Current Above Normal Or Grounded Circuit
SPN 657 FMI 5	Injector Solenoid Driver Circuit - Cylinder #7	High	Engine Injector Cylinder #7 - Current Below Normal or Open Circuit
SPN 102 FMI 3	Boost Pressure Sensor Circuit	Medium	Intake Manifold 1 Pressure - Voltage Above Normal, Circuit Shorted High
SPN 1209 FMI 3	Exhaust Backpressure Sensor	Medium	Engine Exhaust Gas Pressure 1 - Voltage Above Normal or Shorted to High Source
SPN 175 FMI 3	Engine Oil Temperature Sensor	Medium	Engine Oil Temperature 1 - Voltage Above Normal, Or Shorted To High Source

Mercedes-Benz-Specific Diagnostic Tips

Mercedes DAS (Diagnostic Assistance System) required for SCR efficiency adaptation reset.
OM471 BlueTec DEF quality sensor shares harness with tank level — corrosion affects both.
AdBlue crystallization at the doser injector is the leading cause of OM471 SCR derate.