What causes a SPN 3178 code?

SPN 3178 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 3178 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 3178 active.

How do I fix SPN 3178?

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 3178

J1939 SPN 3178 — Body/Chassis parameter

What it means

Aftertreatment SCR Catalyst Reagent Tank Level - Voltage Below Normal, or Rate of Change Out of Range (depending on proprietary manufacturer mapping) — Most commonly associated with body-to-chassis communication regarding auxiliary fluid levels or body system status.