I'm going to post the description from engine-codes.com since it is a big paragraph. You will need a shop manual or else take it to a repair shop that has the equipment and book to check it out.
P0412 TOYOTA Description
An air pump is used on the vehicle to lower tail pipe emissions on start-up. The Powertrain Control Module (PCM
) grounds the Air pump relay control circuit which energizes the Air pump. The PCM
also grounds the Air combination valve vacuum control solenoid circuit,
which energizes the Air vacuum control solenoid. Vacuum is then applied
to both Air combination valve diaphragms which opens the shut off
valves. The PCM
enables both circuits simultaneously when Air system operations id
desired. When the AIR system is active, then Air pump forces fresh air
into the exhaust stream in order to accelerate catalyst operation. The
AIR combination valves replace the conventional check valves. When the
AIR system is inactive the shut off valves prevent air flow in either
The DTC P0412 is detected the the AIR vacuum control solenoid circuit not operating as desired by the PCM.
Read more: http://engine-codes.com/p0412_toyota.html#ixzz2Y7OQTCbb