What causes a SPN 3778 code?

SPN 3778 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 3778 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 3778 active.

How do I fix SPN 3778?

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 3778

J1939 SPN 3778 — Body/Chassis parameter

What it means

J1939 Body/Chassis Parameter Data Not Received. This indicates the engine or transmission controller is expecting a specific data packet from the body controller (e.g., PTO status, parking brake, or chassis load) but is not receiving it via the CAN bus.