Bayern are chasing a miracle at the Allianz Arena after their humbling 3-0 first-leg defeat at the Camp Nou last Wednesday when Lionel Messi capped a dazzling display with two goals.
No team has ever over-turned a three-goal deficit in a European semi-final.
"We all know it's going to be a mammoth task, but we're not going to give up," said Bayern forward Thomas Mueller.
Bayern believe they can claim a historic win with Germany captain Bastian Schweinsteiger suggesting: "Sometimes unbelievable things happen in football and we hope we're going to catch one of those days".
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In Saturday's latest defeat, Bayern crashed 1-0 at home to neighbours Augsburg and had to play 77 minutes with ten-men after reserve goalkeeper Pepe Reina was sent off.
Having also lost 2-0 at Leverkusen the previous week before their drubbing in Barcelona, it is the first time Bayern have failed to score in three consecutive games for 15 years.
But Bayern coach Guardiola, a former Barcelona boss, insists his side must keep their dreams alive.
"The dream is still there and we have 90 minutes. It won't be easy, but I am a fighter.