What are the common causes of P0491?

A clogged secondary air injection pump on bank 1. A blocked secondary air hose or tube on bank 1. A stuck secondary air injection valve on bank 1. A leak in the bank 1 exhaust ahead of the air port.

Command the air pump on a scan tool and listen for it. Inspect the bank 1 air hoses and tube for a blockage. Check the bank 1 air injection valve for sticking. Smoke test the bank 1 exhaust for a leak. Clear the code and retest.

P0491

AIR System Insufficient Flow Bank 1

System: Auxiliary emission controls (P code)
Lamp: Check Engine Light
Category: Powertrain - Auxiliary Emissions Controls

What it means

P0491 means AIR System Insufficient Flow Bank 1.

Check these first

A clogged secondary air injection pump on bank 1
A blocked secondary air hose or tube on bank 1
A stuck secondary air injection valve on bank 1
A leak in the bank 1 exhaust ahead of the air port

What to do next

Command the air pump on a scan tool and listen for it
Inspect the bank 1 air hoses and tube for a blockage
Check the bank 1 air injection valve for sticking
Smoke test the bank 1 exhaust for a leak
Clear the code and retest

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Updated

Generic SAE J2012 definition. Last updated 2026-10-10.