What causes a SPN 6657 code?

SPN 6657 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 6657 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 6657 active.

How do I fix SPN 6657?

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 6657

Cummins fault code 6657

What it means

Aftertreatment 1 Diesel Exhaust Fluid Dosing Unit Heater - Voltage Below Normal or Shorted to Low Source. This indicates an open circuit or high resistance in the heater element within the DEF injector/doser.