P0491 OBD II Trouble Code Secondary Air Injection System Insufficient Flow Bank 1

Symptoms of P0491 OBD II Trouble Code

  • Malfunction Indicator Lamp (MIL) illumination

Common Causes of P0491 OBD II Trouble Code

  • Faulty exhaust manifold check valve
  • A fuse or relay for the secondary air injection pump may be faulty
  • A faulty air pump
  • Leaking vacuum hose
  • A bad vacuum control switch
  • A dislodged a vacuum line
  • A leak in the hoses/piping between the secondary air injection pump and the Combi or secondary air injection
  • A sensor for the secondary air pressure may be faulty
  • The combi valve itself is faulty
  • The secondary air injection port in the cylinder head may be plugged with carbon
  • The secondary air injection ports in the cylinder head may by clogged