What causes a SPN 373 code?

SPN 373 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 373 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 373 active.

How do I fix SPN 373?

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 373

J1939 SPN 373 — Fuel/Air parameter

What it means

Intake Air Heater Relay - Auxiliary Output #1 circuit low/shorted. This monitors the relay that engages the grid heater used for cold starting and emission reduction.