This paper evaluates the concurrent error detection capabilities of system-level checks, using fault and error injection. The checks comprise application and system level mechanisms to detect control flow errors. We propose Enhanced Control-Flow Checking Using Assertions (ECCA). In ECCA, branch-free intervals (BFI) in a given high or intermediate level program are identified and the entry and exit points of the intervals are determined. BFls are then grouped into blocks, the size of which is determined through a performance/overhead analysis. The blocks are then fortified with preinserted assertions. For the high level ECCA, we describe an implementation of ECCA through a preprocessor that will automatically insert the necessary assertions into the program. Then, we describe the intermediate implementation possible through modifications made on gee to make it ECCA capable. The fault detection capabilities of the checks are evaluated both analytically and experimentally. Fault injection experiments are conducted using FERRARI to determine the fault coverage of the proposed techniques.