Air Pump Woes
What is the Air Pump?
The secondary air pump is air injection system that injects air post combustion for a predetermined amount of time after the engine is started. Its only active on startup for a very short time (15-60 seconds) and is inactive after that point. It was introduced in 2006 in the WRX's and in 2007 in the STI's and now most Subaru models have them. The air pump assembly is solely there to combat stringent emission laws. It has no impact whatsoever on fuel efficiency or performance. The total system consists of an Air pump, 2 valves and a crossover pipe.
What goes wrong?
As these cars see more age either the valves tend to get stuck open/closed or the air pump itself fails. When this occurs the vehicle's check engine light (CEL) illuminates as the faults show up as diagnostic trouble codes (DTC). The cruise control light might also illuminate and cause cruise control not to work. The following codes are usually recorded:
P0410 Secondary Air System
P0411 Secondary Air Pump Incorrect Flow
P0413 Secondary Air Pump A Open
P0414 Secondary Air Pump A Shorted
P0416 Secondary Air Pump B Open
P0417 Secondary Air Pump B Shorted
P0418 Secondary Air Pump Relay A
P1410 Secondary Air Pump Valve Stuck Open
P1418 Secondary Air Pump Circuit Shorted
P2431 Secondary Air Pump Circuit Open
P2432 Secondary Air Pump Circuit Low
P2433 Secondary Air Pump Circuit High
P2440 Secondary Air Pump Valve 1 Stuck Open
P2441 Secondary Air Pump Valve 1 Stuck Closed
P2442 Secondary Air Pump Valve 2 Stuck Open
P2443 Secondary Air Pump Valve 2 Stuck Closed
P2444 Secondary Air Pump On Malfunction
If the valves are stuck closed than the daily operation of the engine is not impacted and the vehicle can usually be used as normal. If they are stuck open than it causes the engine to run very rough and almost make the vehicle inoperable.
What is the solution?
Most of the recent cases of failures has gotten Subaru to issue recalls on most problematic models. If you are covered under warranty than its as easy as taking it back to the dealership. If you are not covered by warranty than replacing the parts with OEM parts is an very expensive proposition as the air pump assembly costs hundreds of dollars. Other way to fix this problem is to eliminate the air pump assembly completely (Still need to retain part of one valve as it houses the barometric sensor). It requires the removal of the air pump and both valves and replacing them with block off plates. To turn off the CEL the ECU can be programmed with Cobb Accessport, Ecutek or Opensource to permanently delete the codes from the rom.
Eliminating the air pump assembly and reprogramming the ECU typically costs only fractions of what it will cost to fix or repair the air pump assembly.