What causes a SPN 3421 code?

SPN 3421 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 3421 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 3421 active.

How do I fix SPN 3421?

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 3421

J1939 SPN 3421 — Body/Chassis parameter

What it means

SPN 3421 generic definition relates to a failure or invalid data regarding an Aftertreatment Gas Temperature Sensor (often Bank 1, Sensor 3 in emissions contexts) OR a Body/Chassis data link configuration error depending on the engine manufacturer's Proprietary implementation.