Toyota Corolla 2005 Operating Manual page 7

'05 Corolla_U (L/O 0409)
Leak detection pump
This pump performs fuel evaporation leakage check. This
check is done approximately five hours after the engine is
turned off. So you may hear sound coming from under-
neath the trunk for several minutes. It does not indicate a
malfunction.
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2005 COROLLA from Sep. '04 Prod. (OM12891U)