What causes a SPN 385 code?

SPN 385 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 385 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 385 active.

How do I fix SPN 385?

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 385

J1939 SPN 385 — Fuel/Air parameter

What it means

SPN 385 generically refers to an Auxiliary Pressure input. In many heavy-duty applications, this monitors secondary air or fuel-related pressure parameters that are not part of the primary rail or boost system.