P0491 Subaru Secondary Air Injection System Insufficient Flow Bank 1

Possible causes

– Secondary air pump with no or low air flow
– Secondary air bypass solenoid leaking /blocked or stuck open /closed
– Secondary AIR air hose restricted
– Secondary air vacuum hoses restricted or leaking

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P0491 Subaru Description

The secondary air system detected that there was insufficient mass flow change during pump switching (on/off)