Abstract: A diesel exhaust fluid (DEF) sensor simulator device adapted to be electronically connected to the engine control module (ECM) of a diesel engine and adapted to replace or override electronic signals being sent from an existing DEF header, that is connected between a DEF fluid tank and an ECM of the diesel engine, and send simulated analog or digital signals to the ECM to avoid a sudden reduction in power of the diesel engine, and thereby the power and speed of a diesel vehicle using the diesel engine, during failure of any of the components of the emission system of the diesel vehicle resulting in DEF readings showing that the fuel tank is empty, the fluid temperature is out of a required range, or the fluid quality is out of a required range.