Take a close look at the wiring harness that connects under the driver side of the cab, directly behind the driver front wheel. The harness is usually routed around the cab mount directly to the rear of the driver front tire, behind the mudflap. There’s a known issue where that harness can get chaffed through at that location, and quite often it results in random DEF related issues that are hard to diagnose. This just happened to a truck recently and the owner shared the image with me. He subsequently got the wiring fixed and was reimbursed by Ram.
