Functional diagnostic testing of an electronic circuit board assembly with one or more embedded channels to be tested includes steps of: (a) connecting a channel under test; (b) imposing a known digital or analog voltage, as appropriate for a channel under test, that is generated by a digital or analog output of the electronic circuit board assembly; and (c) comparing data read by the channel under test with the stored value of the imposed voltage and required tolerance to determine whether the channel under test is within specifications. Diagnostic test implemented by digital logic and software residing onboard the electronic circuit board assembly. Execution of software or firmware code segment controls the diagnostic test sequence. Signal switching is facilitated by digital and analog multiplexers.