ThunderMax for 2025 - Up Softail® Models
ThunderMax 309-606 ECM for 2025-Up Softail® Models
For EFI-equipped 2025-up Harley-Davidson® Softail models with Milwaukee-Eight® engines.
Replace your factory engine control module with ThunderMax EFI management and wide-band AutoTune technology. The 309-606 monitors exhaust oxygen and adjusts fueling as you ride, helping match fuel delivery to your motorcycle’s combination of components.
How AutoTune works
Select and load a basemap suited to your motorcycle’s engine, exhaust, and other modifications. After installation and initial setup, AutoTune uses oxygen sensor feedback to make ongoing air/fuel ratio corrections.
The basemap provides your starting calibration. AutoTune refines fueling from that starting point as you ride.
Key features
- Complete replacement ECM: Replaces the factory engine control module.
- Wide-band AutoTune: Uses 18 mm oxygen sensors to monitor exhaust oxygen and make fueling corrections.
- Knock correction: Uses the factory knock sensors to automatically adjust ignition timing when knock is detected.
- Support for performance modifications: Select a suitable basemap when changing components such as the exhaust, intake, or camshaft.
- U.S. engineering and support: Designed, manufactured, and supported in the USA.
Check your exhaust before ordering
ThunderMax requires compatible 18 mm oxygen sensor ports in the exhaust head pipes. Verify that your exhaust has suitable ports before installation.
If your exhaust has smaller ports or no suitable sensor ports, installation of 18 mm weld-in bungs may be required.
Installation and setup
Review the application-specific installation instructions before beginning. Installation includes replacing the factory ECM, fitting the oxygen sensors, and completing the software setup.
Download ThunderMax software · View installation documents
Emissions notice
This product is intended for "RACE READY" vehicles only and is not for sale or use on vehicles otherwise subject to emission control requirements. In the state of California, this product should not be used on any vehicle that is registered for use on public roads. Please view the ThunderMax 50 application guide for "STREET APPROVED" & ARB compliant products.
Key Features
The original industry-leading wide-band AutoTune system, continuously optimizing your motorcycle as you ride for maximum performance and rideability. ThunderMax’s industry-leading wide-band AutoTune system utilizes 18mm oxygen sensors. Most aftermarket exhaust systems are already equipped with 18mm sensor bungs. If your exhaust uses smaller factory-style bungs or does not include oxygen sensor ports, installation of 18mm weld-in bungs may be required for installation.
More than a tuner, ThunderMax replaces the factory ECM with a purpose-built engine management system designed for maximum flexibility and performance.
Whether your motorcycle is stock or heavily modified, ThunderMax adapts to your combination of components without locking you into a single calibration.
The latest ThunderMax software is available as a free download for all ThunderMax users. Whether you’re installing a new ECM, updating firmware, viewing diagnostics, or refining your motorcycle’s calibration, you’ll always have access to the latest features and improvements at no cost.
Find application-specific installation instructions in the ThunderMax support library. Confirm your part number before installation.