The company said Wednesday the fix could take "several days or longer" and did not provide a new date for the flight, which was postponed last week due in part to poor weather.
Spokeswoman Annie Cossette said Bombardier discovered the issue as part of the routine and ongoing review process that's part of first flight preparation.
She said a technical team is now focused on fixing the problem, but provided no further details.
The flight was delayed last Thursday because of conditions, she added, and while "weather was one factor, it was not the only factor."
In addition to the Learjet 85, Bombardier is putting its new CSeries commercial jet through flight testing before receiving certification and entry into service.
The Learjet 85 was initially expected to enter service this summer, but that timeline has now changed. A new date is expected to be announced after the first flight.
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