Secondary air injection system — explained

Your car is probably one of the most important things in your life as it allows easier traveling, but the negative aspect reflects in the gas emissions of internal combustion engines. To get those emissions sorted at least partially, automakers have utilized various solutions over the years, such as a catalytic converter.

Still, some systems reduce the gas emissions level you probably never heard of. One such system is the secondary air injection system, and it got involved in the automotive industry ever since the 70s. Even so, many drivers have never heard of this system before, so that’s what our team is here for – we’ll go over the basic mechanics of the system, its parts, and some potential problems to keep an eye out for.

About the secondary air injection system

The secondary air injection system was introduced in the US market back in the 70s, but it’s not a US-specific trait. German manufacturers like Volkswagen and Audi have mastered their version of the system, and it’s used to reduce the amount of unburnt fuel in the cylinders and reduce gas emissions.

It was the first take on an emissions control system in the automotive industry before the development and implementation of catalytic converters. Once the installation of a catalytic converter became obligatory for car manufacturers, that’s where the orientation of the air injection system shifted.

Hence the name secondary air injection system that rather suits this control system well. As the catalytic converter handled the gas emissions from unburnt fuel and made the exhaust gases more environmentally friendly, this system had another role.

The secondary air injection system is used to support the work of the catalytic converter, and reduce gas emissions on a cold start. Engine start-ups used to produce a lot of gas emissions, and the secondary air injection system deals with that. It prepares the catalytic converter and pumps in extra oxygen to reduce the number of unburnt hydrocarbons released into the atmosphere in form of bad gases upon startup.

How does the secondary air injection system work?

The secondary air injection system works by injecting extra air into the exhaust on a cold start. As a part of the car’s emissions control system, it does this to heat up the catalytic converter and gets it running right after the startup.

By adding extra oxygen and getting it through the converter, the secondary air injection system aids the emissions control right after the engine cranks. It’s much like an EVAP system does, and all these systems work together in your car to control the emissions output.

So, if the vehicle is running with a rich fuel condition and there’s some leftover unburnt fuel, it won’t harm the atmosphere as the emissions are reduced. It all starts with the engine control unit (ECU) since it controls the main parts of the secondary air injection system.

If your car’s ECU determines that additional oxygen needs to flow into the exhaust, it turns on the system. While there might be some slight differences in how a system operates based on the manufacturer, the essential parts of the system are more or less the same.

Parts of the secondary air injection system

There are several main parts of the secondary air injection systems, and they are all controlled by the ECU. If the computer activates the system, here’s a list of parts that work together to provide additional airflow into the exhaust:

• Secondary air pump
• Combination valve
• Intake hose of the secondary air system
• Anti-backfire valve

Let’s see how it all works in practice by going over the entire cycle of the system. Once you start your car, the ECU activates the secondary air pump and air flows into it from the intake. The pump receives teh oxygen through the intake hose.

The air next gets pushed by the pump and reaches the combination valve that’s opened by the ECU when the system is running. Air flows through the valve and enters the exhaust and the catalytic converter, therefore heating it and reducing the emissions level on a cold start. There’s also the anti-backfire valve that cuts the airflow into the exhaust in case of deceleration to prevent late combustion and a backfire.

It all lasts just a minute or up to a few minutes until the converter heats up and then takes the entire emissions control system up its back. Sometimes, the system keeps running for more than 5 minutes and that indicates secondary air injection problems, often accompanied by the “check engine” light.

Problems with the secondary air system

If your car’s secondary air injection system runs smoothly, you shouldn’t see a lot of black smoke coming out of the exhaust on a cold start. However, sometimes a problem could occur caused by the constantly running secondary air injection system.

Most of the problems include a secondary air pump failure, which is the most important part of the system. If you leave the problem unattended, you might face some throttle response and rough idling issues, or frequent backfires right after start-up in case of a bad anti-backfire valve.

Malfunctioning secondary air pump

While you can technically drive your car even without an operable secondary air pump, it comes with a few downfalls. Without a working pump, the system won’t be able to deal with increased gas emissions on a cold start due to leftover unburnt fuel in the exhaust.

It might come accompanied by rough idling right after the engine start-up, and you might fail your emissions test. In some occasions, it even affects the engine performance, since the pump uses air from the air intake and a disturbance in this relationship might negatively reflect the combustion mix.

There are several reasons why a pump might fail, including power grounding or power delivery, vacuum leaks, or simply due to the age of your car.

Combination valve problem

Another malfunction that could make the system inoperable is the combination valve fault. The ECU controls this valve to transfer oxygen pushed by the pump into the exhaust. If the valve gets stuck closed, extra air won’t be able to reach the catalytic converter.

So, trapped air inside could only draw extra air from the air intake and that could cause some erratic idling right after the startup. It’s advisable to fix the valve or the pump should these components fail, to ensure you have a properly-working secondary air system.

Our take

If you haven’t heard of the secondary air injection system before, now you know what it does and how it operates. You can use this knowledge to act swiftly in case the system goes bad and you notice some problems upon starting the engine.

Black smoke due to unburnt fuel or backfires from the exhaust are the main problems you’ll encounter, and a failed secondary air system might result in a failed emissions test. These are the main reasons why you should make sure that it stays functional in your car.