Pipelined A/D Converters have intrinsic high-speed characteristics and are widely used in wide-band communication and video systems. In this paper, we propose a low-cost diagnosis methodology for pipelined A/D converters which employs three techniques in the diagnosis process: (1) time-division- multiplexing (TDM), (2) scan based testing, and (3) VCO based measurement. The last technique is developed to diagnose the most critical mixed-signal functional blocks in the pipelined ADC including the sample-and-hold amplifier (SHA) and the digital-to-analog sub-converters (DASC). It provides a great capability to distinct signals with very small voltage difference and is insensitive to process variations and immune to noise induced errors. The diagnosis methodology is power- and area- efficient because it only needs low-complexity and low-area BIST circuits to accomplish the full diagnosis process. A 12-bit pipelined A/D converter with the proposed diagnosis scheme is designed and simulated using the TSMC 0.25um 1P5M technology to demonstrate the effectiveness of the proposed methodology.