In order to try to comply with the emission laws that some countries have brought in, Subaru and many other car manufacturers have introduced an emission control system that injects additional air into the exhaust to reduce unwanted hydrocarbon emissions. Air is injected into the exhaustfor a predetermined amount of time after the engine is started, typically around 30-60 seconds and is inactive thereafter. It has no effect on engine performance or fuel efficiency. It is solely there for emissions control.
The system consists of an air pump and two valves. When the engine is cold, on start up and for up to 60 seconds air is injected into the exhaust to clean up the extra-rich exhaust and raises the temperature of the exhaust to bring the catalytic converter to operating temperature quickly. To accelerate the activation of catalyst when warming up the engine, the secondary air injection system pumps the air to the exhaust system by an air pressure pump. The secondary air is supplied by the air pump and it is pumped to the exhaust through the air switching valves (AKA Secondary Air Injection Valves).
One of the more common problems with this type of secondary air injection system (and it is not restricted to Subaru cars, many other makes of car also have similar secondary air sytems fitted) is that the secondary air pump is pumping (often damp) air from the atmosphere directly through the secondary air valves and into the exhaust when the engine is cold. Also, a by product of combustion is water and therefore exhaut gas is hot but wet and can find its way into the secondary air valves. This damp air can condense moisure (water) inside the secondary air valves and pump. The air valves close after approximately 40 seconds and the moisture is trapped before the secondary air valves can get hot enough to evaporate the moisture. This can cause corrosion inside the valves and pump leading to the valves(s) sticking open or closed or the pump seizing. These faults will turn on the check engine light and the OBD (on board diagnostic) code reader can show any one (or more) of the following codes:
P0410 Secondary Air System Malfunction
P0411 Secondary Air Pump Flow Abnormal
P0413 Secondary Air Combi Valve Relay Circuit 1 (Low)
P0414 Secondary Air Combi Valve Relay Circuit 1 (High)
P0416 Secondary Air Combi Valve Relay Circuit 2 (Low)
P0417 Secondary Air Combi Valve Relay Circuit 2 (High)
P0418 Secondary Air Pump Relay (Low)
P1410 Secondary Air Injection System Switching Valve Stuck Open
P1444 Secondary Air Injection System Switching Valve Stuck Open
P1418 Secondary Air Injection System Control "A" Circuit Shorted
P2430 Secondary Air Injection System Air Flow/Press Sensor Circ Bank1
P2431 Secondary Air Injection System Air Flow/Press Sensor Circ Range/Perf Bank1
P2432 Secondary Air Injection System Air Flow/Press Sensor Circ Low Bank1
P2433 Secondary Air Injection System Air Flow/Press Sensor Circ High Bank1
P2434 Secondary Air Injection System Air Flow/Press Sensor Circ Interm/Erratic Bank1
P2435 Secondary Air Injection System Air Flow/Press Sensor Circ Bank2
P2436 Secondary Air Injection System Air Flow/Press Sensor Circ Range/Perf Bank2
P2437 Secondary Air Injection System Air Flow/Press Sensor Circ Low Bank2
P2438 Secondary Air Injection System Air Flow/Press Sensor Circ High Bank2
P2439 Secondary Air Injection System Air Flow/Press Sensor Circ Interm/Eratic Bank2
P2440 Secondary Air Injection System Switching Valve Stuck Open Bank1
P2441 Secondary Air Injection System Switching Valve Stuck Closed Bank1
P2442 Secondary Air Injection System Switching Valve Stuck Open Bank2
P2443 Secondary Air Injection System Switching Valve Stuck Closed Bank2
P2444 Secondary Air Injection System Pump Stuck On Bank1
P2445 Secondary Air Injection System Pump Stuck Off Bank1
P2446 Secondary Air Injection System Pump Stuck On Bank2
P2447 Secondary Air Injection System Pump Stuck Off Bank2
Possible Causes:
Short in Air Pump circuit
Blown Fuse
Fault in Air pump assembly
Faulty Pressure Sensor
Pressure Sensor harness is open or shorted
Pressure Sensor circuit poor electrical connection
Secondary Air Valve Stuck Open
Secondary Air Valve Stuck Closed
Air Switching Valve harness is open or shorted
Air Switching Valve circuit poor electrical connection
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