What causes a SPN 3955 code?

SPN 3955 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 3955 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 3955 active.

How do I fix SPN 3955?

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 3955

J1939 SPN 3955 — Body/Chassis parameter

What it means

SPN 3955 refers to the J1939 Body/Chassis parameter. This is a generic network code indicating that the engine controller is not receiving expected data or is receiving invalid data regarding body-specific parameters (like PTO status, outrigger position, or lighting signals).