What causes a SPN 3308 code?

SPN 3308 can be triggered by several issues — see the verified probable causes and step-by-step diagnostics shared by mechanics and owners on OBDIY.

Can I drive with a SPN 3308 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 3308 active.

How do I fix SPN 3308?

Follow the step-by-step diagnostic on this page, then read the verified fixes contributed by other Heavy Truck owners — the answer marked "Verified Cause" worked for the original poster.

OBDIY

J1939 SPN

SPN 3308

SCR Reagent Level Sensor Circuit High Voltage

What it means

The Engine Control Module (ECM) detects an abnormally high voltage signal from the DEF (Diesel Exhaust Fluid) tank level sensor, indicating an electrical open or short to power.