How to Replace an Air Diverter Valve

Today's modern cars, trucks, and SUVs have become highly efficient operating machines. In fact, over the past two decades, the average fuel economy for a six-cylinder consumer sedan has risen by more than 85% as automotive manufacturers continue to evolve the design and applications of fuel and emissions systems. The emissions system in particular has seen dramatic increases in efficiency due in part to the use of components like the air diverter valve or also known as a companion component of the air bypass valves.

The air diverter valve is designed to enhance the clean burning ability of the modern engine by adding clean air into the emissions system in an effort to push out pollutants. The emissions system of most vehicles manufactured after 2000 are controlled by the vehicles ECM (engine control module), which receives information from multiple sensors and makes on-the-fly adjustments to the air diverter valve or secondary air bypass valve to add or reduce the flow of clean air into the system.

The air diverter valve is essentially a vacuum-operated system that supplies pressurized air from the air pump into the exhaust manifold. This pressurized air not helps to complete combustion of unburnt hydrocarbon molecules, but it also provides oxygen to enhance the efficiency of the catalytic converter system. When the unit works as designed, engines can burn up to 90% of the fuel that enters the engine. Without it, the efficiency of the burn can drop to 75 to 80%. It's clearly obvious then that the proper maintenance of this component is critical for the overall performance of today's engines.

Part 1 of 4: Understanding the symptoms of a broken or damaged air diverter valve

When the air diverter valve is not functioning properly, it typically displays a few common warning signs or symptoms that will alert the driver or vehicle owner that a problem exists in the EGR system; which the secondary air bypass valve is a component. Some of the common symptoms of a damaged or worn out air diverter valve may include the following:

The engine runs rough at idle and acceleration. The intent of the EGR system is to balance the burn of unburnt carbon molecules found in the vehicle's exhaust as soon as the engine completes the exhaust stroke. The unburnt hydrocarbons are captured by the EGR system and fresh air is supplied to the exhaust system by the air diverter valve and additional bypass valves. When the fresh air is not supplied, the engine will run rough at both idle and during acceleration. Although the vehicle's ECM is supposed to adjust the fuel/air ratio's if this occurs, the engine won't be able to adjust if it's not receiving a good supply of fresh air.

Fuel economy is reduced. When the air diverter valve is broken, it's not able to help burn the unburnt carbon molecules in the exhaust system. This reduces the fuel efficiency capability of the engine from 90 to 75%, which often means a reduction in fuel economy by 15 percentage points. Initially this will be hard to see at the gas pump, but over a long period of time, it will put a dent in the pocketbook.

The EGR or check engine lights are illuminated on the dash. When this component is broken or not working correctly, the sensors that monitor the EGR system, the exhaust system and intake as well will all trigger OBD-II error codes and store them in the ECM. When this occurs, the check engine light or ERG check light on the dashboard will illuminate. The only way to fix this problem is to replace the air diverter valve and reset the error codes with a professional diagnostic scan tool.

This component is typically found on domestic vehicles, including Ford's and General Motors products. The diagram above shows how the air pump works in conjunction with the air diverter valve/air bypass valve to supply fresh air into the exhaust system. As the diagram indicates, an air supply line runs from the air supply pump, to the air bypass valve. The air diverter valve (in conjunction with the air bypass valve) then supplies three different components (the intake manifold, the air cleaner and the exhaust ports) with air from the pump.

As you can probably assume, when this diverter or bypass valve is broken, clogged or damaged, it will impact the overall operation of your car, truck or SUV. The air diverter valve is designed to last the life of your vehicle, but like any mechanical component, may break or wear out before it should. Some of the most common reasons why the air diverter valve breaks include:

The air supply pump is damaged. When the air pump is not working property, it will not supply the diverter valve with ample air in which to "divert" to the intake, air cleaner or the exhaust system. This can cause the mechanical components inside this valve to wear prematurely.

Debris enters the air bypass valve. If debris enters the air supply system, it can cause clogs and obstructions of air flow inside the diverter valve. This will cause the interior components inside this unit to heat and can cause the valve to break.

Over exposure to excessive heat. Since this valve is often located on the top of the engine and next to the exhaust system, it can wear out due to excessive heat; especially if it's made from plastics or polymers. Most air diverter valves are metallic, but some are made from hardened plastic.

As the above image indicates, there are three air supply lines that are attached to this component. The air diverter valve is typically secured to a bracket with two bolts (which is what the two holes on the left side of the unit are for). The vacuum port is attached to the EGR vacuum, the outlet to exhaust system secures to the exhaust ports and the inlet is supplied from the air pump or smog pump. In order to remove this component, you'll need to detach the three tubes, remove the two bolts and install the replacement system. The job is fairly easy to complete and can be done in a manner of minutes as long as you don't have to remove multiple components in order to gain access.

Part 2 of 4: Preparing the vehicle for replacing the air diverter valve

This component is typically attached on top of the engine and the lines that need to be removed are fairly simple to access. Due to this fact, you won't have to raise the vehicle on a hydraulic lift or jack stands. However, sometimes if this component is damaged, the smog pump or air pump will also have damage done to it as well. This is commonly due to excess pressure that builds up inside the smog pump when the diverter valve is unable to distribute the pump's air supply.

The damage that happens to the smog pump is typically due to seals or gaskets that burst due to the excess pressure. As such, it's a good idea to inspect the smog pump on the vehicle at the same time you're replacing the air diverter valve or bypass valve.

To remove the air diverter valve, you'll only need a few supplies and tools for most cars, trucks, and SUVs. However, like any other replacement project, it's always a good idea to purchase and review the service manual for the vehicle you are working on; as instructions, supplies and tools may be different for each vehicle.

  • Tip: It's a good idea to download OBD-II error codes before determining that this component is faulty as the error code will give you a good starting place to diagnose the precise component that is damaged or faulty. It's very common for a sensor to also be damaged, which can create similar symptoms as a damaged or faulty air diverter valve. Make sure to inspect both sensors and the valve for damage or faulty connections before replacing.

Materials Needed

  • Flat blade screwdriver
  • Pair of needle nose pliers
  • Other tools for removing engine covers and other components in the way (refer to your service manual for detailed instructions and tools needed)
  • Penetrating oil (WD-40 or PB Blaster works best)
  • Safety glasses
  • Socket and ratchet set (typically 10mm bolts)

Part 3 of 4: Replacing the air diverter valve

The process for removing and replacing the air diverter valve will be unique for each vehicle; as in some cases, this component is attached to the air bypass valve. For purposes of this HOW TO article, we'll assume that you're replacing a singularly air diverter valve; which is common with Ford and GM four cylinder engines and some six cylinder engines. This component is typically located on the passenger side of the engine compartment and secured to a bracket near the exhaust system.

The steps noted below are general replacement steps. Please make sure to refer to your vehicles service manual for exact procedures and tools needed to complete this replacement projects safely.

Step 1: Remove the battery connections. Anytime you work under the hood of the vehicle, it's recommended to remove the positive and negative battery cables from the terminals. Remove the positive and negative terminals first then proceed.

Step 2: Remove engine covers: On most vehicles, you'll have to remove the engine cover in order to have access to the air diverter valve. Refer to your vehicle service manual for steps on how to complete this process. In general, you'll follow these steps noted below:

  • Remove the bolts securing the engine cover to the brackets underneath
  • Remove air filter or air cleaner lines attached to engine cover
  • Remove electrical harnesses or sensor attachments from engine cover
  • Remove the cover from the vehicle's engine compartment

Step 3: Locate the air diverter valve. The image above shows what the air diverter valve typically looks like and how it's connected to the engine. As you can see, there is a main hose with a hose clamp on the left side; which connects to the air pump (smog pump), the vacuum line on the right side (with the 90 degree fitting) and a third line underneath that attaches to the exhaust ports. The unit itself is secured to a bracket that the unit slides inside of and attached by two bolts.

Step 4: Remove the vacuum line first: Before removing any other components, remove the vacuum line connection first. Sometimes the problem with the air diverter valve is that the vacuum line has been cut, is damaged or not securely fastened to the air diverter valve.

Before you remove it, inspect the vacuum line attachment. If it was not secured correctly, reattach it and test-start your car before replacing this part. If the problem still exists, continue to replacing your air diverter valve.

Step 5: Remove smog pump line: Once you've removed the vacuum line, the next hose to remove from the air diverter valve is the one attached to the air pump or smog pump. First, using the needle nose pliers, remove the hose clamp secured on the fitting.

Slide the hose clamp off the male fitting on the air diverter valve. Once the clamp has been removed, using both hands, grab the air diverter valve with your right hand and start to take the hose off with the left hand.

Most of the time this hose is very tight onto the air diverter valve, so you might have to use a flat blade screwdriver to carefully pry the hose off. Another trick is to use a bit of penetrating oil to spray on the inside of that hose to provide some lubrication. You'll need to add penetrating oil to the inside of the hose for the install, no need to worry about damaging the smog pump hose using that trick.

Step 6: Remove bolts securing the air diverter valve to the bracket. There are usually two bolts that secure the air diverter valve to the bracket on the engine. Using the right sized socket (typically 10mm), remove the two bolts.

On most vehicles, the bolts are secured to the brackets themselves, but may be secured with a nut on the other side. Refer to your service manual for exact removal instructions for your vehicle.

Step 7: Remove the exhaust manifold hose. Once the air diverter valve has been loosened from the bracket, you'll be able to remove the exhaust manifold connection which is usually on the bottom of the valve.

This will be usually connected with a hose clamp, so use the same method for removing this hose as you did in Step 5 above. Once this hose has been removed, take the old air diverter valve out of the engine compartment and prepare for installing new unit.

Step 8: Install the new air diverter valve. The process for installing the new air diverter valve is exactly opposite from the removal noted above. Follow these general steps but refer to your vehicle's service manual for exact instructions.

  • Place new air diverter valve inside the bracket
  • Install the exhaust manifold hose onto the bottom of the valve
  • Install the air diverter valve onto the bracket & tighten screws
  • Install the smog pump hose
  • Install the vacuum line connection on the air diverter valve
  • Install engine cover and supporting components that you need to remove earlier
  • Reconnect battery cables

Part 4 of 4: Testing the repair

When you've replaced the air diverter valve, the first thing you'll need to do is to reset the OBD-II error codes stored in the vehicle's ECM. If you're not able to do this, contact an ASE certified mechanic to complete this step for you. If the error codes are not cleared before you start the vehicle, it will disable the EGR system and the repair of your air diverter valve will be irrelevant.

Once you've cleared the error codes, testing the repair is rather simple. Follow these steps to ensure your air diverter valve replacement was done correctly.

Step 1: Start the engine with the hood open.

Step 2: Look underneath the air diverter valve and check all three lines (the vacuum, smog pump and exhaust) and make sure they are not leaking.

Step 3: Test the throttle response. Get inside the vehicle and test the throttle response by quickly pressing the gas pedal a few times on and off. Make sure the engine revs up smooth and also revs down smoothly.

Step 4: Take vehicle on a test drive. It's best to test drive your vehicle during a 10 to 15 mile test drive. Make sure you test on the highway to verify that the acceleration is good.

Step 5: Have your emissions tested. In most cases, the reason that this part is replaced is because it failed emissions inspection. Have the emission checked to verify the repair was done correctly.

As you can see, the process for replacing this component is rather easy. However, if you've read this instructional article and determined that you don't feel comfortable completing this project, contact one of our ASE certified mechanics from YourMechanic and they'll be happy to complete the air diverter valve replacement project for you.

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Subaru Impreza H4-2.5L - 30,000 Miles Maintenance Service - Los Angeles, California
very professional. on time, ready to work, absolutely wonderful. drove the car today this morning on the freeway. the car runs so smooth and better. very satisfied with his service and i do recommend him to anyone looking for trustworthy professional service.
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BMW 328i L6-3.0L - Air Diverter Valve - Moreno Valley, California
I got a diagnosis from Jay on my BMW's Service Engine Soon light and he traced the problem to the Secondary Air Injection Valve. Jay explained to me and I learned the functionalities of the Secondary Air Injection System. He then replaced the offending part when it became available in a few days. I was also pleased that I received credit for the cost of diagnosis toward the cost of replacing the valve (parts and labor). YourMechanic is the way to go!


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Audi A4 Quattro L4-2.0L Turbo - Air Diverter Valve - Woods Cross, Utah
Ryan is great! Arrived promptly and did a great job replacing a part in a difficult place with siezed bolts.


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Ford Fusion L4-2.3L - Air Diverter Valve - Vancouver, Washington
Prompt and courteous! Did the work as promised and also did an inspection of my ford fusion. Thanks goodness he did because the radiator cap was broken. Saved me the hassle of overheating the engine. Thanks Robert!

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