What causes a SPN 221 code?

SPN 221 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 221 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 221 active.

How do I fix SPN 221?

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 221

J1939 SPN 221 — Fuel/Air parameter

What it means

Engine Intake Manifold 1 Temperature sensor voltage is below normal. This indicates an electrical short to ground on the manifold air temperature (MAT) sensor.