A system for built-in instrumentation, applied to a fleet of bus vehicles, is evaluated as one element of a continuing program to improve the effectiveness and efficiency of bus maintenance operations. The evaluation study concentrated on a built-in instrumentation system, originally developed for military vehicles, in which the connections, sensors, and transducers required for test and diagnosis are permanently installed on a vehicle and terminated in a single “diagnostic” connector. Testing is accomplished by connecting analytic instrumentation to the diagnostic connector. Several designs of analytic instruments exist which provide for varying degrees of test comprehensiveness.This paper describes the peculiarities of bus maintenance, the evaluation process, tradeoffs related to test system requirements versus benefits derived, and how the instrumentation system design was tailored from a military to a commercial application. The results of the evaluation are presented along with a review of other consideration factors including fuel shortage, fleet capital investment spiral, and cost and availability of maintenance personnel.