An airport spokeswoman says the issues are mostly resolved and that nearly all the delays have been dealt with.
The problem started Saturday when all of the busy airport's check-in counters malfunctioned, resulting in delays as passengers were instead checked in manually.
The Greater Toronto Airports Authority and the airlines brought in additional staff — including IT experts — to deal with the problem.
The latest hold-up at Pearson followed the cancellation and delays of hundreds of flights earlier in the week.
Pearson officials triggered a so-called ground stop early Tuesday, preventing North American flights from landing for more than eight hours.
Also on HuffPost