Improvements in vehicle diagnostics are evolving both from the development of new sensors and from the extension of standard sensor capabilities made possible by modern electronics and processing techniques. Accordingly, the effective application of sensors to vehicles is an overall system problem. Foremost among the design considerations are the test parameters that are indicators of faults, the accuracy with which they must be measured, and the methods available for evaluating, processing and displaying those parameters. Next are the considerations of survival and performance in the automotive environment, the operator's method of performing the test, and applicability to a broad spectrum of vehicles.This paper discusses criteria for sensor selection from the viewpoint of a developer of systems for the malfunction diagnosis of vehicles with spark or compression ignition engines. The focus is on pressure transducers. The considerations, however, are generally applicable to all sensors.