What causes a SPN 4209 code?

SPN 4209 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 4209 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 4209 active.

How do I fix SPN 4209?

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 4209

Allison transmission code P4209

What it means

Selective Catalytic Reduction (SCR) System - Reagent Tank Heater Control Circuit/Open. This code refers to a failure in the heating element circuit for the Diesel Exhaust Fluid tank.