Secondary Air Injection System Insufficient Flow Bank 1
The ECM has detected insufficient airflow from the Bank 1 secondary air injection system, which pumps fresh air into the exhaust after cold start to help the catalytic converter reach operating temperature faster.
SeverityMinor
CategoryEmissions
Est. Repair Cost$200–$900
Code TypePowertrain
DIY RepairProfessional
⚡ Common Causes
›Failed AIR pump
›Clogged check valve
›Failed AIR solenoid
›Vacuum line leak
⚠️ Symptoms
›Check engine light
›Emissions test failure
✅ How to Fix — Step by Step
Step 1:Test AIR pump
Step 2:Inspect check valves
Step 3:Test solenoid
Step 4:Repair vacuum lines
💡 Pro Tip: Test the AIR pump and check valves separately — a failed check valve lets exhaust flow backward into the pump, which is a common cause of pump failure.
Repair Cost Estimate
Full Repair Estimate
$200–$900
DIY Possible?
PRO
Severity
Minor
Frequently Asked Questions
What does OBD2 code P0491 mean?+
P0491 stands for Secondary Air Injection System Insufficient Flow Bank 1. The ECM has detected insufficient airflow from the Bank 1 secondary air injection system, which pumps fresh air into the exhaust after cold start to help the catalytic converter reach operating temperature faster.
What causes code P0491?+
Failed AIR pump; Clogged check valve; Failed AIR solenoid; Vacuum line leak
How do I fix code P0491?+
Test AIR pump; Inspect check valves; Test solenoid; Repair vacuum lines
How much does it cost to fix P0491?+
Estimated repair cost for P0491 is $200–$900.
Is P0491 DIY-friendly?+
P0491 typically requires professional equipment and a qualified mechanic.
