A DIAMOND DA-42 TWIN STAR ACFT ANNUNCIATOR LIGHT ON THE CAPTAIN'S G-1000 DISPLAY PANEL SHOWED 'YELLOW' INDICATING ENG CONTROL UNIT ECU-A AND ECU-B HAD FAILED ON THE LEFT ENG.

Narrative

DURING MISSED APCH PROCS AFTER A PRACTICE ILS APCH OVER ZZZ1 ARPT; THE L ENG OF THE TWIN-ENG DA42 HESITATED WITH ANNUNCIATORS ON THE G-1000 PANEL INDICATING THAT BOTH FLT COMPUTERS (ECU A AND B) ON THE L ENG HAD INDICATED A FAILURE DURING NORMAL OPS. THIS FAILURE WAS INDICATED BY A YELLOW (NOW RED) INDICATION THAT SOMETHING UNUSUAL HAD HAPPENED IN BOTH THE PRIMARY AND SECONDARY ECU'S FOR THE L ENG. IMMEDIATELY; I TOOK CTL OF THE ACFT AND REQUESTED A PRIORITY LNDG AT ZZZ1; TO EVAL THE ACFT AND ITS SYS. APCH PASSED US BACK TO THE CTL TWR WHO ALLOWED US TO MAKE AN IMMEDIATE LNDG WITH NO ADDITIONAL INDICATION; SENSORY OR ELECTRONICALLY; THAT ANY PROBS EXISTED WITH THE L ENG. UPON LNDG; I TAXIED THE ACFT TO THE RWY 29R RUN-UP AREA; SHUT DOWN; AND LET THE SYS 'REST' FOR ABOUT 10 MINS. UPON REBOOTING THE ELECTRICAL SYS; NO ECU INDICATORS WERE DISPLAYED AND ENGS STARTED WITHOUT INCIDENT. AFTER A COMPLETE RUN-UP (BASED ON MANUFACTURER PROCS) WAS CARRIED OUT; I DEEMED THE ACFT AIRWORTHY AND DEPARTED ZZZ1 REQUESTING FLT FOLLOWING BACK TO ZZZ2. CLBING AT NEARLY VYSE (82 KIAS TO GAIN ALT AS QUICKLY AS POSSIBLE) TO 4500 FT MSL; I NOTICED THAT THE L ENG ECU A AND B ANNUNCIATORS AGAIN DISPLAYED THAT AN ANOMALY HAD TAKEN PLACE WITHIN THE COMPUTERS (NO INDICATION WAS GIVEN FROM THE ENG THAT ANY PROB HAD OCCURRED). I WAS ABOUT 1/2 OF THE WAY BACK TO ZZZ2 WHEN THIS OCCURRED. I CONTINUED TO CLB TO 6500 FT WHILE NOTICING NO OTHER ENG ANOMALIES OR SENSORY INDICATIONS THAT A PROB EXISTED WITH THE L ENG. UPON REACHING 6500 FT; PWR WAS REDUCED ON THE ENGS AND A GRADUAL DSCNT WAS STARTED IN CASE MORE SERIOUS ISSUES AROSE WITH EITHER ENG. APCH XFERRED US TO ZZZ2 TWR WHO ASKED US IF WE NEEDED ASSISTANCE. SINCE ALL ENG INSTS AND THE ENGS THEMSELVES SEEMED OK; I NOTIFIED THEM THAT ALL WAS WELL AT THE MOMENT AND I WOULD KEEP THEM INFORMED. THE LNDG TOOK PLACE WITHOUT INCIDENT WHILE THE L ENG'S A AND B ECU ANNUNCIATORS WERE STILL BEING DISPLAYED. AT THE CONCLUSION OF THIS FLT; I REMOVED THE ACFT FROM SVC AS THE ECU A AND B ANNUNCIATORS SEEMED UNRELIABLE; OR; THE ECI'S MAY BE IN NEED OF SVC. AT NO TIME DID EITHER ENG FAIL; BUT STEPS WERE TAKEN TO ASSURE THE SAFETY TO THE FLT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THE ANNUNCIATOR LIGHTS ARE AT THE BOTTOM OF HIS G-1000 FWD DISPLAY SCREEN. ALTHOUGH THE 'YELLOW' LIGHT INDICATED FAILURE; ALL OTHER INDICATIONS SHOWED NORMAL. MAINT TROUBLE SHOOTING NOTED A SENSOR INDICATED THE MANIFOLD PRESSURE WAS TOO HIGH. A MANIFOLD PRESSURE CHECK WAS PERFORMED AND FOUND TO ACTUALLY HAVE LOW PRESSURE. A SENSOR HAD FAILED; CAUSING THE ANNUNCIATOR 'YELLOW' LIGHT TO APPEAR. SENSOR WAS REPLACED AND THIS SEEMS TO HAVE CORRECTED THE PROBLEM.