P0491 Code - Secondary Air Injection System Insufficient Flow Bank 1

What Does P0491 Mean?

The PCM has detected a problem in the secondary air injection system. The secondary air injection system uses ambient air, which is pumped into the engine exhaust, to reduce emissions.

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What are the common causes of P0491 ?

Typical common causes of code P0491 could include the following-

• Defective check valves that let water through to freeze in the air pump during cold spells. Note that improved check valve designs have largely eliminated this problem.
• Defective air pump
• Damaged, shorted, burnt, disconnected, or corroded wiring and connectors.
• Blown fuse (Where fitted)
• Defective air pump relay
• Vacuum leaks in systems that use vacuum to control check valves
• Leaks in pressure hoses
• Blocked air passages that prevent injected air from reaching the catalytic converter

How do you troubleshoot P0491 ?

Solutions for P0491 may include:

• Replacing any damaged wiring, connectors, or other electrical components
• Replacing the secondary air injection pump
• Replacing the pump’s one-way check valve
• Repairing or replacing any damaged vacuum hoses or fittings which could be causing a vacuum leak
• Replacing pump fuses
• Cleaning the cylinder head

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