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.
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HOMESERVICE MANUALSMERCURY2009MILAN PREMIER, 3.0 1, AWDREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROLS - POWERTRAIN DTC CHARTS & DESCRIPTIONS (EXCEPT DIESEL & HYBRID)DTC DIAGNOSISDTC P0491: - SECONDARY AIR INJECTION (AIR) SYSTEM INSUFFICIENT FLOW (BANK 1)
2009 Mercury Milan Premier, 3.0 1, AWD
DTC P0491: - Secondary Air Injection (Air) System Insufficient Flow (Bank 1)
2009 Mercury Milan Premier, 3.0 1, AWDSECTION DTC P0491: - Secondary Air Injection (Air) System Insufficient Flow (Bank 1)
DTC P0491: - SECONDARY AIR INJECTION (AIR) SYSTEM INSUFFICIENT FLOW (BANK 1)
| Description: | The AIR system detected that there was insufficient mass air flow change during pump switching (ON/OFF). | ||
| Possible Causes: |
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| Diagnostic Aids: | Measured air flow is less than expected. Visually inspect the secondary AIR inlet hose. | ||
| Application | Key On Engine Off | Key On Engine Running | Continuous Memory |
| All | - | GO to Pinpoint Test HM . | GO to Pinpoint Test HM . |
RENDER: 1.0x
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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.