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.
Circuit Description
Secondary Air Injection (AIR) system reduces hydrocarbons, carbon monoxide and oxides of nitrogen exhaust emissions. When engine is started, ECM commands AIR pump relay and AIR solenoid valve on, injecting clean air into engine exhaust ports. ECM switches AIR system off when oxygen sensors become active. Airflow is controlled by vacuum operated cutoff valve. Vacuum to valve is controlled by AIR solenoid valve. A check valve close to engine prevents hot exhaust gasses from backing up into AIR system.
ECM uses short term fuel trim to diagnose AIR system. When AIR system is enabled, ECM monitors short term fuel trim. If short term fuel trim goes below a threshold, ECM interprets this as an indication that AIR system is operational. When AIR pump is disabled, short term fuel trim should return to normal.
For duplication of DTC, short term fuel trim must not go above expected value within 6 seconds.
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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.
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