Technical Documents

Subaru Wrx Forester Sti Secondary Air Pump Fault

What’s a Secondary Air Pump?

To meet the ever more stringent emissions targets being placed on manufacturers, Subaru introduced a secondary air injection system on all turbocharged models manufactured from around 2004 onwards. Specifically, the system is fitted to the 2.5L turbo engine found in the MY06-on Forester XT, MY07-on Liberty GT and MY06-on Impreza WRX/STi models. What does the system do exactly? To help combat unwanted hydrocarbon emissions, air is injected post combustion for a predetermined amount of time after the engine is started. The system is only operational for a small amount of time post start (the amount of time varies depending on engine temperature, but is typically around 30-60 seconds), and inactive thereafter. It has no effect on engine performance or fuel efficiency it is solely there for emissions control.

What Is The Fault And What Causes It?

The system consists primarily of an air pump assembly, two air valves and a crossover pipe. As vehicles the systems are fitted to age, we are increasingly coming across several variations on the same fault. Either the pumps themselves fail, or one or both of the air valves seize open or closed. This triggers an engine fault condition and the ECU will show a “Check Engine Light”on the dash. The cruise control system will also cease to operate (and where fitted, the light on the dash switch flashes). The codes can be checked with a generic scan tool, Subaru Select Monitor or aftermarket software on a laptop (such as EcuTek DeltaDash or another open source derived product).

One or more of the following Fault Codes will be recorded in memory as Current, Historic or both:airpumpfault_1

  • 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 Combi Valve Open Seized
  • P1418 Secondary Air Pump Relay (High)
  • P2431 Secondary Air Pressure Sensor Property
  • P2432 Secondary Air Pressure Sensor (Low)
  • P2433 Secondary Air Pressure Sensor (High)
  • P2440 Secondary Air System Open Seized (Bank 1)
  • P2441 Secondary Air System Closed Seized (Bank 1)
  • P2442 Secondary Air System Open Seized (Bank 2)
  • P2443 Secondary Air System Closed Seized (Bank 2)
  • P2444 Secondary Air Pump On Malfunction

The Solution

We haven’t seen a successful repair of any components to date, and to complicate matters Subaru only sell the replacement parts as a “kit” which presently costs around AU$3700-4500 depending on where you source the parts. The system can’t be removed from the car easily without triggering more faults either (the Atmospheric pressure sensor, used by the engine management system for ongoing day to day engine related calculations, is fitted within the primary air valve assembly). Fortunately there is another solution which is both CHEAPER and gives you the option of added performance as a bonus! Using EcuTek software, we have the ability to access your factory engine management system and change a whole host of parameters. Generally we use this to increase performance on standard and modified cars by optimising the engines operational parameters (fuelling, boost control, ignition advance, variable cam timing and so on), but it can also be used to access both the parameters that run the Secondary Air System and the fault codes which are or aren’t triggered in the event of a fault condition being present.

With that in mind, you have 3 options. All will permanently rectify the Secondary Air System fault condition, restore Cruise Control operation AND be a fraction of the OEM replacement and repair cost, but depending on your budget it is also a convenient time to consider a performance upgrade as well!

  • Option One Retain factory tune in OEM specification and rectify fault conditions only
  • Option Two Upgrade to an entry level performance tune designed for the same 95 RON fuel that the factory tune runs on, and rectify the fault conditions. Gains are typically around 8-10kw depending on your specific vehicle model.
  • Option Three Upgrade to our XA Performance Kit. Designed for 98 RON fuel gains of around 15-20kw depending on your specific vehicle model are typical.

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