A failure diagnosis apparatus and method permit specification of a failed atmospheric pressure sensor in an engine control apparatus having redundant pressure detection systems to ensure failsafe control of the engine. The apparatus includes a calculating unit that calculates a difference between a first atmospheric pressure and a second atmospheric pressure detected in respective pressure detection systems. A first comparing unit outputs an alarm when the difference is larger than a threshold value. A difference calculating unit calculates a first difference between the first atmospheric pressure and a manifold pressure. A difference calculating unit calculates a second difference between the second atmospheric pressure and the manifold pressure. A second comparing unit compares the first and second differences in response to output of the alarm from the first comparing unit while an engine is stopped. The sensor having abnormal function corresponds to the one for which the difference is larger.