What Is Secondary Air Injection System Insufficient Flow Bank 1?

If you’ve ever had a check engine light appear on your dashboard, you know how frustrating it can be. One possible reason for this warning is a secondary air injection system insufficient flow bank 1 issue.

In today’s blog, we’ll take a closer look at the secondary air injection system, how it works, and what can cause this error code.

So, whether you’re an experienced mechanic or a driver who wants to understand more about your car, keep reading to learn more!

What Does The Secondary Air Injection System Insufficient Flow Bank 1 Code Mean?

secondary air injection system insufficient flow bank 1
Secondary Air Injection Insufficient Flow

The secondary air injection system insufficient flow bank 1 code is the code P0491 and sometimes P0492.

It means the secondary air injection (SAI) system (in the engine side containing cylinder 1) is malfunctioning.

This is a component of the exhaust system, where oxygen from the outside reaches the exhaust after a cold start.

This is to warm up the catalytic converter and handle certain exhaust gasses like carbon monoxide and other hydrocarbons.

It reduces the total emission rate by pumping ambient air into the exhaust.

When the SAI system cannot work as it should be, the powertrain control module (PCM) will detect it and send a message to the code reader, so the code will appear.

What Are The Usual Causes And Symptoms Of The P0491 Code?

When it comes to the secondary air injection insufficient flow, there are some causes and symptoms that you can look up for:


The P0491 Audi or P0491 BMW code refers to an issue with the secondary air injection system – specifically, a low flow detected on bank 1. There are many potential culprits behind this code.

First, the air pump injects air into the exhaust system to help reduce emissions. If the pump fails, it cannot provide the necessary airflow, resulting in the air injection error code.

The air supply line that delivers air to the exhaust system can become clogged with debris or carbon buildup, preventing the necessary airflow and triggering the code.

The check valve hinders exhaust gasses from entering the secondary air injection system is also a usual cause.

If it malfunctions, it can allow exhaust gasses to enter the system, causing damage and triggering the code.

Moreover, problems with the wiring or electrical component in the secondary air injection system and vacuum leak can also trigger the P0491 code.

But sometimes, the leak might stem from a bad valve cover gasket, so check it carefully.


Rarely do codes P0491 and P0492 result in noticeable symptoms. The check engine light should illuminate, and the air pump may make odd noises, such as hissing.

It’s conceivable that you only experience the check engine light or occasionally notice slow acceleration or stopping when idling.

How Do You Fix The Code P0491

secondary air injection system
Fix The Code P0491

In this part, we will show you some steps for fixing the problems:

Step 1

Keep records of all accessible error codes and freeze frame information. If an intermittent defect is later identified, this information may be useful.

Step 2

Ensure that the engine is cool, and use the handbook to find and recognize all necessary components.

Additionally, you should discover, route, and color-code any related hoses, vacuum lines, and wires for reference purposes.

Step 3

If the scanner tool has control systems, use them to instruct the air pump to turn on.

Since most pumps produce a vacuum-like sound when operating, whether the pump won’t come on, check to see if the fuse (if one is installed) has blown or if the pump’s control relay is functioning.

When a fuse has to be replaced, do so; however, should a relay appear to be malfunctioning, inspect it using the manual’s directions.

Step 4

Disconnect the air pump’s wires and supply DC current to the connections’ contacts if changing the fuse fails to activate the pump, or it doesn’t start after examining the sensor and its control circuit.

On the other hand, examine the pump’s wiring for continuity, grounding, and resistance in case a DC current powers it.

To ensure that all electrical values match the manufacturer’s requirements, verify all measurements to the manual’s specifications and make the necessary corrections.

After the repair is completed, scan the system to see whether any codes reappear.

Step 5

If the pump starts up fine without making noise, but the code still pops up, you should separate the pressure lines before checking the valve.

Then, ensure the pump is producing airflow. Vice versa, examine the pump feed line for clogs and limits.

In case of necessity, clear away all blockages and change the air filter. Here, examine the hoses for cracks, leaks, splits, or other problems that might result in pressure loss if the pump generates airflow.

Then, consider reconnecting or replacing the hoses.

Step 6

Be ready to test the check valve’s functionality yourself if the hoses leading to it are functional. Suppose your scanner has a control mechanism; use it to tell the valve to open.

Otherwise, take a multimeter to verify the current in the connection.

Step 7

If an engine vacuum powers the check valve, detach the valve from the vacuum source, and link the pump to the valve, but leave the hose attached to the valve disconnected.

Then, open the valve with a vacuum to ensure that air flows through it.

Now, check any vacuum lines running to the valve for signs of damage that might result in vacuum loss if the vacuum remains constant and airflow from the pump passes through the valve.

If necessary, swap out broken vacuum lines.

Step 8

Let’s say the check valve is performing as planned, all vacuum lines, wiring, and pressure hoses are serviceable, and the air pump is still working and supplying airflow.

Find the location where the pressure lines link to the engine.

This point could be on the exhaust manifold in certain applications and on the cylinder head in others.

No matter where the pressure line is connected, you must detach it, turn on the air pump, and open the check valve to let air into the system.

In most circumstances, checking the airflow by putting your fingertip over the air outlet is sufficient to establish affirmative airflow.

Step 9

Beside being used to find an AC leak, compressed air can also clear any potential obstacles or constraints in the pressure hose before removing it from the engine.

Attach the pressure hose once freed up, but not to the engine mounting point. Then, verify the system’s pressure sensor’s functionality before reconnecting the pressure pipe to the engine.

Step 10

The holes through which air reaches the exhaust system are likely clogged when there is airflow at the installation site and the airflow pressure sensor is fully operational.

This is rather typical, and in certain circumstances, you can open several channels by sticking a piece of hard wire through the hole.


cleaning audi secondary air port via combi-valve area
Question Of Secondary Air Injection System

Can I Drive With Code P0491?

No. It is generally not recommended to drive with a diagnostic trouble code, including P0491.

This code indicates an issue with the secondary air injection system, which can impact the vehicle’s emissions and overall performance.

What Is The Price Of A Secondary Air Injection System?

The cost of a secondary air injection system can be different based on the make and model of the vehicle, as well as the specific part that needs to be replaced.

Generally, a new secondary air injection system can range from around $200 to $1,000 or more.


In summary, the P0491 code indicates that the secondary air injection system insufficient flow bank 1.

It’s important to have the issue diagnosed and repaired promptly to ensure compliance with emissions regulations and prevent further engine damage.

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