What causes a SPN 7021 code?

SPN 7021 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 7021 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 7021 active.

How do I fix SPN 7021?

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 7021

Cummins fault code 7021

What it means

Aftertreatment 1 Diesel Exhaust Fluid Tank Heater Control - Voltage Above Normal or Shorted to High Source. This indicates the ECM detects an open circuit or high voltage on the DEF tank heater valve control circuit.