SCR/DEF Warning Lights — What They Mean & What To Do

Check Engine (amber) STOP (red) DEF Light (blinking)

When these lights appear together—amber check-engine, red STOP, and a blinking DEF light—your truck likely has an SCR (Selective Catalytic Reduction) system fault. This is more than low fluid; a blinking DEF lamp indicates an active emissions fault and the truck may derate (limit power/speed) if not corrected.

What to do now

Pull over safely. Avoid long driving with these lights on.
Check DEF level and top up with ISO 22241-compliant DEF if needed.
Do not ignore or clear codes. Derate can follow quickly.
Book diagnostics. Mobile Diesel Repair, LLC will pinpoint SCR/DEF issues (pump, injector, heater, NOx sensors, wiring, etc.).

Common symptoms

Reduced power / speed limit (derate)
“Service DEF/SCR System” messages
Check-engine + red STOP illuminated
DEF light blinking (not just solid)

Book Service with Mobile Diesel Repair Call Now: (775) 964-4495

Dashboard with amber check-engine, red STOP, and a blinking DEF light near the DEF gauge—indicating an SCR system fault.

A blinking DEF lamp typically signals an active SCR/DEF system fault.
Service available in West Wendover, Nevada and surrounding areas.