Alert Message from Freightliner Custom Chassis on Cummins DEF Software Update

[Neal]

Dear FCOC Members,

Cummins has announced software updates designed to give operators more time to address certain diesel exhaust fluid (DEF) and selective catalytic reduction (SCR) system problems before engine power or vehicle speed is reduced.

In its July 6, 2026 announcement, Cummins reported that revised calibrations were being made available for more than 1.5 million engines, including certain truck applications dating back to engine model year 2017 and certain motorcoach applications dating back to 2018. Availability varies by engine platform and model year.

An October 15 follow-up confirmed that tens of thousands of engines had received the updates and that implementation remained on track across applicable on-highway and non-road products.

For eligible engines, the changes extend the time before certain DEF quality or tampering-related derates occur. The July announcement also described an increase in final reduced-speed limits from 5 mph to 25 mph for applicable heavy-duty trucks and tractors, and from 5 mph to 50 mph for eligible motorcoaches.

An important distinction for our members: Cummins’ motorcoach classification refers to passenger-carrying coaches and should not be assumed to include recreational motorhomes. Your applicable speed limit and update eligibility must be confirmed for your specific engine.

These updates do not eliminate the need for DEF or repairs. DEF remains required, emissions requirements remain in effect, and inducements associated with low DEF tank levels remain in place.

Before scheduling service, ask your Cummins distributor or authorized dealer to:

• Check your engine serial number (ESN) for eligibility and current update availability.
• Confirm which revised inducement settings apply to your motorhome.
• Provide the cost before authorizing the work. Cummins’ published technical guidance states that this calibration change is not covered under warranty.

Use your engine’s model year when checking eligibility, as it may differ from your motorhome’s advertised model year.

These changes offer welcome flexibility when certain DEF-related problems occur, but availability and benefits depend on the individual engine. Checking with Cummins before your next service appointment will help you determine whether the update is available for your coach.

For details, please see:
Cummins’ July 6 announcement
Cummins’ October 15 update
Cummins’ technical explanation and planned rollout schedule

Safe travels,

Steven Bertling
President
Freightliner Chassis Owners Club
(321)704-0695