An method and apparatus for error checking. A known test pattern is written into a predetermined byte of a scan line. The method may include generating a known test pattern in a byte of a scan line and transmitting the scan line data through a first data path. The scan line data at the end of the first data path may be evaluated to determine if the test pattern is still in the predetermined byte of the scan line. If the pattern in the predetermined byte is correct, the test pattern may be removed from the predetermined byte and the scan line data may be transmitted to a print engine. If the pattern in the predetermined byte is incorrect, then a signal may be sent to terminate the transmission of the scan line data.