What causes a U3221 code?

U3221 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 U3221 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with U3221 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

Log in Sign up

OBD-II

U3221

Manufacturer-specific network code U3221

What it means

Network error relating to the Telematics or Fleet Management gateway system. This affects remote diagnostics.

Sign in to view symptoms, probable causes, diagnostic steps, severity, and related codes

Log in Sign up free