Diesel fault codes

Look up OBD-II and SAE J1939 diesel fault codes — what each one means, likely causes, and how urgent it is.

All fault codes

Diesel fault codes

Engine Oil Pressure — Below Normal (Most Severe)

Intake Manifold (Boost) Pressure — Data Erratic

Engine Coolant Temperature — Above Normal (Most Severe)

Injection Rail Pressure — Above Normal (Most Severe)

Injection Rail Pressure — Below Normal (Most Severe)

DEF Tank Level — Below Normal (Most Severe)

DEF Tank Level Sensor — Voltage High

Aftertreatment Intake NOx — Data Erratic

Aftertreatment Outlet NOx — Data Erratic

DPF Intake Gas Temperature — Data Erratic

DPF Outlet Gas Temperature — Above Normal (Most Severe)

DPF Differential Pressure — Above Normal (Most Severe)

DPF Differential Pressure — Data Erratic

DEF Dosing Unit — Current Below Normal/Open

DEF Quality — Below Normal

DPF Soot Load — Very High (Most Severe)

DPF Soot Load — High (Least Severe)

DPF Ash Load — High (Moderate)

SCR Operator Inducement — Severe

EGR Differential Pressure — Voltage High

EGR Temperature — Above Normal (Most Severe)

DEF Dosing Pressure — Below Normal

SCR Conversion Efficiency — Low (Moderate)

VGT Turbocharger Actuator — Not Responding

Fuel Delivery Pressure — Below Normal (Most Severe)

Fuel Rail/System Pressure Too Low

Fuel Rail/System Pressure Too High

Mass Air Flow Circuit Range/Performance

Coolant Temp Below Thermostat Regulating Temp

Turbocharger Overboost Condition

Turbocharger Underboost Condition

EGR Flow Insufficient Detected

EGR Flow Excessive Detected

EGR Control Circuit

Exhaust Pressure Sensor Circuit

Exhaust Pressure Sensor Range/Performance

Engine Oil Pressure Sensor/Switch High Voltage

Exhaust Gas Temp Sensor 1 Circuit High (Bank 1)

Fuel Injector Driver Circuit (Bank 1)

Glow Plug Module Control Circuit

Fuel Rail Pressure Low

Diesel Particulate Filter Efficiency Below Threshold (Bank 1)

Reductant Level Sensor Performance

Reductant System Performance

Reductant Tank Temperature Sensor Circuit High

Exhaust Gas Temp Sensor Range/Performance (B1S1)

Exhaust Gas Temp Sensor Range/Performance (B1S2)

Reductant Pressure Too Low

SCR NOx Catalyst Efficiency Below Threshold (Bank 1)

Intake Air Temperature Sensor 1/2 Correlation

NOx Sensor Circuit (Bank 1 Sensor 1)

Barometric Pressure Circuit Range/Performance

Turbo Boost Pressure Not Detected — Mechanical

DPF Restriction — Ash Accumulation

DPF Differential Pressure Too Low (Bank 1)

DPF Differential Pressure Too High (Bank 1)

DPF Pressure Sensor Range/Performance

DPF Pressure Sensor Circuit Low

DPF Regeneration Frequency

DPF Soot Accumulation