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Trouble Code

P0491 Code: Secondary Air Injection System Insufficient Flow Bank

This is the OBD-II generated trouble code for Secondary Air Injection System Insufficient Flow Bank 1 that indicates that there is some problem on that side of the engine which contains cylinder 1..

Various components are equipped in the car that elevates its performance. Fuel emission is one of the major factors that affect the performance of the vehicle. This is detected by the P0491 error code. If your vehicle is diagnosed with this error code that means that there are some faults in the emission system of your vehicle.

Definition of P0491 error code

This is the OBD-II generated trouble code for Secondary Air Injection System Insufficient Flow Bank 1 that indicates that there is some problem on that side of the engine which contains cylinder 1.

What does the Po491 error code mean?

The secondary air injection system of the vehicle are equipped with an air pump, an exhaust manifold, an input check valve, a vacuum control check, and an electrical input circuit for vacuum hoses that use fresh air, injects into the exhaust, dilute the mixture, and facilitates the low emission production.

P0491_error_code

The message includes information about the air pressure flow through the system and is sent to the PCM to get converted into the voltage signals. If there are some faults in the air check pumps and the check valves the reading of the manufactures does not match with the received reading. Then, the PCM indicates that there are some faults in the emission system and the secondary airflow is very low in bank 1cylinder 1 of the vehicle, and the P0491 error code is generated.

Possible cause of the P0491 error code

There are many causes of the P0491 error code, some of them are:

  • Faults in the secondary air pressure sensor
  • Damages in wiring or connectors, loose connections with sensors
  • Faults in system relay
  • Faults in one-way check valve in the air inlet
  • Faults in the air injection pump or fuse
  • Heavy Vacuum leak
  • Blockage in secondary air injection ports

Symptoms of the P0491 error code

There are various symptoms of the P0491 error code, other than the check engine light is on, sometimes you can hear a hissing noise from the air injection system of the car that is a clear symptom of a vacuum leak. Many other symptoms are generated by the P0491 error code, some of them are:

  • Mechanical noises that are caused by the damaged air pump
  • Hesitation in acceleration
  • Rough idle
  • Check engine light illuminates
  • Failed Emission test

The severity of the P0491 error code

The P0491 error code is not more serious, but it can cause stalls while driving. The secondary air injection system is directly linked to the fuel emission of the vehicle if this system gets affected then your vehicle may fail an emission test. Some other faults can generate in other components of the vehicle that can affect your driving.

How to diagnose the P0491 error code?

For the diagnosis of the P0491 error code, mechanics start their diagnosis by using a scanning tool to record freeze frame data. To verify that the code is not in an intermittent situation, the codes are set again and the driver takes a test drive to check if the code returns.

P0491_error_code
Close up of the engine control unit of the car, multicolored wires plug, contacts – a wiring of a truck car. Electrical communication, wires in an old car

If the code returns, the next step they will do to check the wiring harnesses of the air injection pump. If they found burnt, damaged, or short wiring, they will repair or replace them.
After the wirings, they will check the system hoses and check for cracks, damages, or any other problems that may cause the hose to leak.
If the error code remains so, they will check the system fuses.
After checking system fuses they will go for the one way check valve to ensure that air passes through one direction only.
After testing all the components, if the error code remains so, they will now inspect the secondary air injection system pump.

How to fix the P0491 error code of the vehicle?

After the diagnosis of the possible causes that can illuminate the check engine light because of the P0491 error code, there are some solutions to fix that error code that includes:

  • Repair or Replacement of damaged one-way check valve pump to let air pass through one direction
  • Repair or Replacement of secondary air injection pump
  • Repair or Replacement of damaged connectors, wiring, and other electrical components
  • Repair or Replacement of damaged vacuum hoses or fittings that causes air leaks
  • Repair or Replacement of pump fuses
  • Cleaning the contaminated cylinder head

The P0491 error can affect the driving of the vehicle by stalling during driving. The secondary air injection pump can cause a failed emission test that affects the performance of the vehicle. So, it is advisable to fix the P0491 error code as early as possible to maintain the performance of the vehicle.

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