This paper describes a technique which uses the Differential Non Linearity (DNL) test data for fault location and identification of the analog components of a flash ADC. In a flash ADC, a fault in the analog subcircuit is uniquely reflected in the transfer function and therefore also in DNL data.This property is exploited to locate a fault and to identify the error value in analog components of the flash ADC. The technique proposed here relies only on DNL test data. Thus the diagnosis can be carried out using at-operating-speed test data. The paper presents relationship between each fault case and its respective DNL pattern. Fault simulation results of a small flash ADC are presented.