What was found
PDX - "L FADEC" CAUTION MSG. ALL ENGINE INDICATIONS NORMAL. RETURNED TO THE FIELD. LANDED BELOW MAX LANDING WEIGHT. MDC MESSAGE L FADEC FAILED SWITCH VERSION - DISAGREE SOFTWARE CHECK SUMS (A+B) DISAGREE. LABEL BIT 355A - 23 (BUILT IN TEST) FLAGGED WITH ONE. ATTEMPTED CLEAR OF MESSAGE BY MEANS OF IBIT - MESSAGE CHANGED TO FADEC FAULT 1 WITH THE SAME FAULT IN MDC. REMOVED AND REPLACED LEFT FADEC AS A PRECAUTIONARY MEASURE IAW CRJ-700 MM TASK 73-21-01-000-801 + 73-21-01-400-801. PBIT CHECK GOOD. NO MDC MESSAGES RELATED TO FADEC. RETURNED TO SERVICE.