Southwest flight No. 3519 took off from San Francisco International Airport for Denver but landed in Oakland after the problem was reported, Southwest Airlines spokeswoman Katie McDonald said.
The plane landed safely at 7:48 a.m., Oakland Airport spokeswoman Rosemary Barnes said.
The plane will remain at the airport as mechanics look at it to fix the problem, McDonald said.
The 137 passengers were moved onto another flight and will arrive in Denver two hours later than initially scheduled, McDonald said.