What causes a SPN 387 code?

SPN 387 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 387 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 387 active.

How do I fix SPN 387?

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 387

J1939 SPN 387 — Fuel/Air parameter

What it means

The engine ECM has detected a functional failure in the air/fuel ratio control for the intake air heater or cold-start auxiliary burner system.