What causes a SPN 4257 code?

SPN 4257 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 4257 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 4257 active.

How do I fix SPN 4257?

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 4257

SPN 4257 — Engine Brake Output 1

What it means

The Engine Control Module (ECM) has detected an electrical fault (open circuit, short to low, or short to high) in the control circuit for Engine Brake Output 1.