P0491 Fault Code

Secondary Air Injection System (Bank 2)

• What does that mean?
• Symptoms
• Causes
• Solutions

The P0491 error code indicates an issue with the Secondary Air Injection System in Bank 2. This system is designed to reduce emissions during cold starts by injecting air into the exhaust stream, helping to promote combustion of unburned fuel. When the vehicle's onboard diagnostic system detects that the secondary air injection system is not functioning correctly, it triggers the P0491 code.

What are the symptoms of the P0491 code?

When dealing with a P0491 error code, you may experience:

• Increased emissions during cold start conditions
• Potential engine performance issues, such as rough idle
• Check Engine Light illuminated on the dashboard
• In some cases, the vehicle may fail emissions testing due to high pollutant levels

What causes the P0491 code?

Several factors can cause the P0491 fault code, including:

• A malfunctioning secondary air pump
• Blocked or damaged air injection hoses
• Issues with the air control valve
• Faulty electrical connections or wiring in the system
• Problems with engine vacuum, affecting operation of the air injection system

How to fix P0491?

To address the P0491 code, mechanics typically follow these steps:

• Inspect the secondary air injection pump for proper operation
• Check the air injection hoses for blockages or leaks
• Test the air control valve for functionality
• Inspect electrical connections for any signs of corrosion or damage
• Clear the fault codes and perform a road test to ensure the issue is resolved