What causes a SPN 635 code?

SPN 635 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 635 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 635 active.

How do I fix SPN 635?

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 635

J1939 SPN 635 — Engine Management parameter

What it means

SPN 635 relates to Engine Compression Brake Output #1. It indicates an electrical fault (open circuit or short) in the solenoid circuit that controls the first stage of the engine brake.