Dortmund sit joint second-bottom of the table at the halfway point of the season, having won just four of their 17 top-flight fixtures this term.
Jurgen Klopp's men - who won back-to-back titles in 2011 and 2012, and have finished runners-up to Bayern Munich in the last two seasons - have been better in the UEFA Champions League, and face a last-16 tie with Juventus next month.
Qualification for Europe's premier club competition next season is looking unlikely currently, but Kehl believes Dortmund can make big improvements in the second half of 2014-15.
"The scale of the problem is high but we also have big plans for the second half of the season," Kehl told a news conference during Dortmund's mid-season break in La Manga.
"It is a new situation. We have many strengths and we should remind ourselves of them in the second half.
"We have to play a certain type of football - and we have not done that well in the first half of the season."
Kehl is set to retire at the end of the campaign, having been succeeded as captain by Mats Hummels in August.
"My role in the team has not fundamentally changed, although Mats is now the man who leads us," the 34-year-old added.
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