SR22
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Flight Crew Last 90 Days 150; Flight Crew Total 13000; Flight Crew Type 1700
Human-Machine Interface; Distraction
Aircraft Equipment Problem Less Severe; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Human Factors; Aircraft
On an ATC heading of 270; I was given a descent from current altitude of 8;000 feet to 6;000 feet. I selected Vertical Speed ALT on the autopilot control and verified preselected 6;000 feet and VS/Alt on the Primary Flight Display (procedure). Shortly thereafter; I got an 'Engine Sensor Not Communicating' message on my MFD followed by a 'Check Fuel Quantity' message (Which was now indicating '0') and a 'Battery Discharge' message. (These messages cycled intermittently for the remainder of the flight.) While investigating the messages; I noted I had passed through 6;000 feet still in a descent and the autopilot was in the VS only. I was pulling back on the stick and climbing through 5;580 feet when ATC called and stated; 'Callsign; maintain 6;000 feet;' to which I responded; 'Correcting to 6;000.' The next call from ATC was to change over to [frequency]. It appears the spurious signals or lack thereof interrupted the autopilot's capture mode and I did not catch this. There was no autopilot Off Tone to indicate AP Off nor did it sound when manually disconnecting it during subsequent trials. I became distracted by the MFD messages while in flight and should have caught the autopilot mode change. I grounded the aircraft for Maintenance to work the issue.
SR22 pilot reports an 'Eng Sensor not communicating' message on his MFD during descent with autopilot engaged and altitude capture active.  During troubleshooting the autopilot descends 500 feet below selected altitude before detection.