No ACARS messages of any serviceability issues with the aircraft. Or more likely, there were some ACARS messages delivered to MAS maintenance control, but MAS have not been able to make sense of them – and are thus not willing to release them to the public.
According to
Reuters:
"There were no signals from ACARS from the time the aircraft disappeared," a source involved in the investigations said.
Although
Malaysian are less specific:
All Malaysia Airlines aircraft are equipped with continuous data monitoring system called the Aircraft Communications Addressing and Reporting System (ACARS) which transmits data automatically. Nevertheless, there were no distress calls and no information was relayed.