P0491 GMC 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
– 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 GMC Description
The secondary air system detected that there was insufficient mass flow change during pump switching (on/off)
GMC Vehicle:GMC Acadia,GMC Canyon,GMC Envoy,GMC Savana 1500,GMC Savana 2500,GMC Savana 3500,GMC Sierra 1500,GMC Sierra 2500 HD,GMC Sierra 3500 HD,GMC Terrain,GMC Yukon,GMC Yukon XL 1500,GMC Yukon XL 2500,