L5P Owners: Seeing A DEF Message After Flashing?

If you have a 2017+ L5P Duramax, don't panic if you see a DEF-related message after flashing your truck. In many cases, this is a normal part of the process and can be resolved in just a few steps.

Using EZ Lynk?

If you're flashing with EZ Lynk, you will need to flash the file titled:

"DEF Message Reset"

This file is designed to clear the DEF message that may appear after programming.

Don't Forget To Clear Your Codes

After flashing your truck, clear all diagnostic trouble codes (DTCs) using your scan tool or tuning device.

Temporary codes can be set during the programming process and are often responsible for warning messages that appear immediately after the flash.

2022+ L5P Owners

On 2022+ L5P Duramax trucks, the DEF message may return after performing the DEF Message Reset. This is normal while the remaining DEF fluid continues to bleed out of the system.

If the message comes back, simply flash the "DEF Message Reset" file again as needed until the system has fully cleared.

Still Having Issues?

If you've completed the steps above and are still experiencing issues, check your CAN bus plugs to ensure they are fully seated and connected properly. A loose or improperly connected CAN bus plug can cause communication issues that may result in warning messages or unsuccessful flashing.

Before Contacting Support

Before submitting a support request, please make sure you have:

• Flashed your desired tune.

• Flashed the "DEF Message Reset" file (EZ Lynk users).

• Cleared all diagnostic trouble codes (DTCs).

• For 2022+ L5Ps, reflashed the "DEF Message Reset" file if the message returned while the remaining DEF fluid continued to bleed out.

• Verified that all CAN bus plugs are securely connected.

• Started the truck and checked whether the message or codes return.

Following these steps resolves the vast majority of post-flash DEF message concerns.

If you're still experiencing an issue after completing the checklist above, our support team is happy to help. When reaching out, please include your truck's year, tuning platform, any diagnostic trouble codes that return, and a brief description of what the truck is doing so we can assist you as quickly as possible.