What causes a U3440 code?

U3440 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 U3440 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with U3440 active.

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

OBD-II

U3440

Manufacturer-specific network code U3440

What it means

This code denotes a specific communication disconnect between the Powertrain Control Module and a peripheral controller, often related to emissions or auxiliary power.