Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Secondary Air Injection (AIR) System Monitor - Electric Secondary Air Injection Pump System
The Secondary Air Injection (AIR) System Monitor is an on-board strategy designed to monitor the proper function of the secondary air injection system. The AIR monitor for the electric secondary air injection pump system consists of 2 monitor circuits: an AIR circuit to diagnose concerns with the primary circuit side of the AIR relay, and an AIR monitor circuit to diagnose concerns with the secondary circuit side of the AIR relay. A functional check is also carried out that tests the ability of the AIR system to inject air into the exhaust. The functional check relies upon HO2S sensor feedback to determine the presence of air flow. The monitor is enabled during AIR system operation and only after certain base engine conditions are first satisfied. Input is required from the engine coolant temperature (ECT) or cylinder head temperature (CHT), intake air temperature (IAT), crankshaft position (CKP) sensors and the HO2S monitor test must also have passed without a fault detection to enable the AIR monitor. The AIR monitor is also activated during on-demand self-test.
- On the primary side of the AIR relay, open and short circuit faults are detected during normal operation by the PCM output driver. This circuit energizes the relay and the vacuum-operated check and solenoid control valves.
The DTC associated with this test is DTC P0412.
- On the secondary side of the AIR relay, the AIR monitor circuit is held low by the resistance path through the AIR pump when the pump is off. If the AIR monitor circuit is high there is either an open circuit to the PCM from the pump or there is power supplied to the AIR pump. If the AIR monitor is low when the pump is commanded on, there is either an open circuit from the AIR relay or the AIR relay has failed to supply power to the pump.
The DTCs associated with this test are DTCs P2257 and P2258.
- The functional check may be done in 2 parts: at startup when the AIR pump is normally commanded on, or during a hot idle if the startup test was not able to be carried out. The flow test relies upon the HO2S to detect the presence of additional air in the exhaust when introduced by the secondary air injection system.
The DTC associated with this test is DTC P0411.
- The MIL is activated after one of the above tests fail on 2 consecutive drive cycles.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.