WOMS
P code powertrain Medium severity

P0491 Secondary Air Injection System (Bank 2)

The OBD2 code P0491 indicates a malfunction in the secondary air injection system for bank 2, which is responsible for reducing emissions during cold starts by injecting air into the exhaust system

Definition

The OBD2 code P0491 indicates a malfunction in the secondary air injection system for bank 2, which is responsible for reducing emissions during cold starts by injecting air into the exhaust system

Common causes

  • Faulty secondary air injection pump
  • Blocked or damaged air injection hoses
  • Failed check valve
  • Faulty air injection relay
  • Electrical issues (wiring or connectors)
  • Vacuum leaks
  • Faulty engine control module (ECM) or software issues
  • Clogged or damaged air injection system components

Common misdiagnoses

  • Faulty oxygen sensors
  • Exhaust leaks
  • Vacuum leaks
  • Faulty air pump
  • Clogged or restricted air passages
  • Faulty relay or wiring issues
  • Engine control module (ECM) issues
  • Incorrectly installed or damaged secondary air injection system components

Troubleshooting steps

  1. 1. Check for Additional Codes

    Use an OBD-II scanner to check for any other related trouble codes. This can provide more context for the issue

  2. 2. Inspect the Secondary Air Injection System Components

    Air Pump: Check the operation of the secondary air pump. Ensure it is functioning properly and is not blocked or damaged

  3. 3. Check Valves

    Inspect the check valves for proper operation. They should open and close as intended without leaks

  4. 4. Hoses and Connections

    Look for any cracked, broken, or disconnected hoses that could affect air flow

  5. 5. Examine Electrical Connections

    Inspect the wiring and connectors associated with the secondary air injection system. Look for corrosion, loose connections, or damaged wires

  6. 6. Test the Air Pump Relay

    Check the relay that controls the secondary air pump. Ensure it is functioning correctly and is receiving power when needed

  7. 7. Check for Vacuum Leaks

    Inspect for any vacuum leaks in the system that could affect the operation of the secondary air injection system

  8. 8. Inspect the Engine Control Module (ECM)

    Ensure that the ECM is functioning properly and is not causing the issue. Sometimes, a software update may be needed

  9. 9. Perform a Visual Inspection

    Look for any signs of wear, damage, or corrosion in the components of the secondary air injection system

  10. 10. Test the System Operation

    If possible, perform a functional test of the secondary air injection system. This may involve monitoring the system while the engine is running to see if it activates as expected

  11. 11. Clear Codes and Test Drive

    After performing repairs or adjustments, clear the trouble codes and take the vehicle for a test drive to see if the code returns

  12. 12. Consult Repair Manual or Professional Help

    If the issue persists after performing these steps, consult a repair manual for your specific vehicle or seek assistance from a professional mechanic.Additional Notes

  13. 13. Environmental Conditions

    Be aware that the secondary air injection system typically operates during cold starts, so testing may need to be done under those conditions

  14. 14. Emissions Testing

    If you are in an area with emissions testing, addressing this code is important for passing inspection. By following these troubleshooting steps, you should be able to identify and resolve the issue related to the P0491 code