P0412 - Jetta Volkswagen Cars & Trucks

Ull need to scanit w a factorytool at a privateshop. It reads a datastream to pinpoint issues. Those portabl readers are general. Dont just replaceparts n hope. Oldercars can hav worn wireharness causin weird problms too. Unplug computer n cleanpins..dirt is common in aging vehicles creating issues. Since its jyst an emmission thing udont need to worry its runnin too lean or sumthin crucial

This is the electrically driven secondary air injection air pump. Please read all the information at the link before you buy or replace any parts. In most cases the entire air injection pump assembly must be replaced.
P0412 Secondary Air Injection System Switching Valve Circuit Malfunction

code p0412 refers to secondary air injection (AIR) solenoid A---circuit malfunction===causes wiring---air solenoid---ECM
replace the AIR solenoid.

You can read about the P0412 code here: http://www.obd-codes.com/p0412

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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 direction.
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

P0412 - Secondary Air Injection System Switching Valve 'A' Circuit Malfunction

Possible causes- Faulty Air Pump inoperative
- Air bypass solenoid harness is open or shorted
- Air bypass solenoid circuit poor electrical connection

p0412 Secondary air injection switching valve A circuit
Right side of engine compartiment. ( underhood fuse block )
- Air pump fuse 50A- Air control valve relay- ignition1 fuse 10A ( positive for the relay )The secondary air injection pump relay is located near radiator surge tank.Left front of engine compartiment = Secondary air injection pump

P0412 is related to the Secondary air injection system that inserts fresh air into the exhaust to promote a more complete fuel combustion.

P0412 Pulsed secondary air injection solenoid circuit, with seeing it and what it is doing i would guess replace the secondary air injection solenoid control valve.