Choosing the correct response from a subset of alternatives is a fundamental problem and particularly demanding where conflicting response tendencies are evident. One phenomenon in this context is the congruency sequence-(Gratton effect), for which different theoretical explanations have been put forward. A critical aspect that differs between these explanations is the expectancy of what will happen in forthcoming trials. In the current study we examine the relevance of expectancy for sequence congruency effects and related neurophysiological processes using a flanker task in which we manipulate the probability that the n+. 1 trial presents the same stimulus-response mapping than the n trial. We ask what cognitive subprocesses involved in response selection may be modulated by expectancy effects. To distinguish different subprocesses probably modulated by expectancy effects we use event-related potentials (ERPs) in combination with source localization techniques. The data show that cognitive subprocesses modulated by expectancy depend on the nature of expected transitions between succeeding trials. Expectancy effects only affected trial transitions within the same category (i.e., 'compatible-compatible' and 'incompatible-incompatible'), but not between compatibility categories (i.e., 'compatible-incompatible' and 'incompatible-compatible'). On compatible trial transitions attentional selection processes operating via the precuneus mediated expectancy effects, while on incompatible trial transitions inhibitory processes were modulated that were mediated via the medial and middle frontal gyrus, the orbitofrontal cortex, the insular and the parahippocampal gyrus. Conflict monitoring processes per se were not modulated by expectancy effects. The data shows that there are different subprocesses underlying the influence of expectancy on sequence effects during response selection.