What causes a SPN 4815 code?

SPN 4815 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 4815 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 4815 active.

How do I fix SPN 4815?

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 4815

Engine Cooling Fan Thermal Switch Position

What it means

This code indicates a fault in the feedback or control circuit for the engine cooling fan switch/hub. The Engine Control Module (ECM) detects an unexpected voltage or signal from the fan's position/engagement sensor.