What was found
DURING THE TAXI OUT, THE AIRCRAFT RETURNED TO THE GATE ON TWO OCCASIONS FOR ECU FAIL WARNING MESSAGES. THE FIRST GATE RETURN, MAINTENANCE INSPECTED AND REPLACED THE LEFT HAND 1.8 SENSOR, (P/N 8720194), AND THE LEFT HAND NP SENSOR, (P/N 8720190). OPERATION CHECKS WERE COMPLETED, AND THE AIRCRAFT WAS RELEASED FROM MAINTENANCE. THE FLIGHT RETURNED TO THE GATE WITH ANOTHER ECU FAIL INDICATION. MAINTENANCE INSPECTED AND REPLACED THE LEFT HAND INTERCOMPRESSOR BLEED VALVE, IN ACCORDANCE WITH DORNIER MAINTENANCE MANUAL 75-31-01. OPERATION CHECKS WERE COMPLETED AND THE AIRCRAFT WAS RETURNED TO SERVICE.