What causes a SPN 2977 code?

SPN 2977 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 2977 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 2977 active.

How do I fix SPN 2977?

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 2977

J1939 SPN 2977 — Aftertreatment/Emissions parameter

What it means

SPN 2977 generally refers to an Aftertreatment Exhaust Gas Temperature or DEF Dosing system performance issue, often indicating that the actual dosing rate does not match the commanded rate.