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

The error code P0491 can be defined as Secondary Air Injection System Insufficient Flow Bank 1. This trouble code indicates that there is an issue on the side of the engine which contains cylinder #1.

This diagnostic fault code is a generic powertrain code, which means that it would apply to the OBD-II-equipped vehicles. The specific repair steps can vary as it depends upon the vehicle’s make and model.

What Does Code p0491 Mean?

Diagnostic trouble code (DTC) P0491 stands for “Secondary Air Injection Insufficient Flow Bank 1.” It is logged once the vehicle’s powertrain control module (PCM) perceives that there is a possible issue within the SAI system.

This code is logged once the PCM determines that the secondary air flow in bank 1 is too low. Bank 1 refers to the side of the engine where cylinder #1 is located.

P0491 OBD-II Code

To understand this code better, let’s discuss the main function of an SAI system. It supplies air needed for the oxidizing process in the exhaust manifold or the catalytic converter. This system is also commonly called AIR, which means air-injection reaction.

A vehicle’s SAI system is equipped with an air pump. This pump may be driven by either the engine’s drive belt (older vehicles) or an electric motor (newer vehicles).

Airflow from the pump is directed to either the catalytic converter or the exhaust manifold to aid in the oxidation of harmful exhaust gases. On most vehicles, the PCM manages a collection of solenoid-operated valves to direct airflow from the pump.

Once the PCM perceives that the secondary air flow in bank 1 is significantly low for a certain period of time, it will trigger the P0491 trouble code.

For more information on SAI that could help you fully understand P0491, read our technical discussion about the secondary air injection system.

Potential Causes of a p0491 Code

  • Some faults in the system relay
  • Leakage in the vacuum
  • Issue of clogged secondary air injection parts
  • Defects in the air injection pump or fuse
  • There can be a bad one-way check valve in the air inlet
  • Damaged wiring or connectors, or loose sensor connections
  • The secondary air pressure sensor might be bad

p0491 Code Symptoms

  • Appearance of the check engine light
  • There can be a hissing sound from the air injection system
  • Issue of sluggish acceleration
  • Stalling while idling or at start-up
  • Abnormal noises from the air pump.

How to Fix p0491

 Diagnosis Of Engine Error

  • An OBD-II scanner should be used to verify the set code and record other relevant data
  • You must verify that it isn’t an intermittent condition by clearing the codes, road testing the vehicle, and scanning the computer again to see if they return , Inspecting the air injection pump wiring harness and other connections for damage.
  • Make sure to inspect the system hoses and fittings for heat damage, cracks, and other conditions that may be causing a leak.
  • The system fuses should then be tested.
  • Testing the one-way check valves to ensure that air is only able to go through in one direction.
  • Test the secondary air injection system pump.

Fix p0491

  1. You must replace the damaged wiring, connectors & other electrical components
  2. The secondary air injection pump should be replaced.
  3. Replace the pump’s one-way check valve.
  4. If there are any damaged vacuum hoses or fittings which could be causing a vacuum leak then they should be repaired or replaced.
  5. Make sure to replace the pump fuses.
  6. Carefully clean the cylinder head.

How Much Does It Cost to Fix a p0491 Code?

To fix an OBD-II P0491 code, which indicates a problem with the secondary air injection system, you can expect to pay between $400 and $1200 depending on the specific cause of the issue.

Common repairs including replacing the secondary air injection pump, vacuum hoses, check valves, or addressing wiring problems, and factoring in labor costs which can range from $80-$140 per hour.