Before intake air enters the engine, it flows into the intake manifold. This component distributes the intake air to the cylinders.
BMW uses the DISA valve to direct how quickly air takes this movement. When it is in the closed position, there is more space to collect resources. If it is open, more compression occurs to refine speed and power.
Efficient engines want the air in the engine system to work with its timing to create an efficient performance profile.
In BMW engines equipped with the DISA valve, the ECU is responsible for controlling when it opens and closes.
Diagnosing a Failing BMW DISA Valve
The Differenzierte Sauganlage (DISA) valve was first included with BMW vehicles in 1995. It is responsible for air control as it comes into the intake, creating performance improvements by controlling airflow through the engine system. It was eventually retired in 2006 when the M54 engine was discontinued.
The DISA valve is responsible for controlling the journey that air takes while coming into the engine system through the intake.
It uses a flap that opens and closes, lengthening or shortening the path that the airflow takes when moving to the cylinder chamber.
When the engine is at a low RPM, the DISA valve stays closed. That action forces the air to take a longer journey to the cylinder chamber. As the RPMs increase, the valve opens to let the airflow have a shorter path through the engine system.
The shorter path has less space for the air, which naturally compresses it during its movement. That makes the airflow more combustible, optimizing the engine’s performance while providing a boost to the vehicle’s fuel economy.
What Are the Symptoms of a Failing DISA Valve?
When a DISA valve is not operating as it should, you may see any or all of the following symptoms while driving your BMW. It is important to review the status of this component regularly since its disintegration could ruin the engine.
The DISA valve is a plastic component that is held in place by a metal pin. If either element breaks, it gets sucked into the engine.
1. Rattling Noises
The most common symptom of a failed DISA valve is a rattling noise that comes from your vehicle’s intake system.
When the seals start wearing out on this component, more air can slip past the closure in the open or closed positions.
That activity creates a rattle as the valve attempts to stop the air, but it gets forced through anyway.
The noise is similar to someone rapidly knocking on your front door at home or tapping the fender.
Although it can be constant, it’s typically heard during times when accelerating rapidly or idling for a longer period.
When the DISA valve seals have severe damage, it’s possible to hear rattling and whistling sounds coming from the engine bay.
The easiest way to determine if you hear a rattle from the DISA valve is to unplug the component. When there isn’t power to it, the valve stays in the open position, eliminating the rattle from it being closed.
2. Poor Gas Mileage
BMW included the DISA valve for more than a decade because it recognizes that airflow control could improve a vehicle’s performance.
When this component no longer operates as it should, you will see fewer efficiencies in all aspects of its operation.
That leads to poor gas mileage while driving. This change can be significant. You could see 20% to 30% less range when your DISA valve is leaking air.
The only way to correct this issue when it occurs is to have the DISA valve replaced.
3. Power Loss
BMW gave the DISA valve one job. It needs to open when the engine requires more air and close when it doesn’t have that requirement.
When it starts malfunctioning, you can find power loss happening in one of two ways – although rarely both.
- You might notice a lack of low-end torque during your initial acceleration or while driving at low RPMs.
- There could be power loss in the mids or highs as you strive for peak performance from the engine.
This symptom is reflective of where you have the most issues with the opening or closing of the DISA valve.
If the valve leaks air while closed, you’re more likely to experience problems with your low-end torque while driving.
When it allows more air than necessary on the upper end, you won’t have as much compression available to maximize your power.
4. Coding Error
Some drivers don’t experience any symptoms from a DISA valve failure. Their only clue that something is wrong comes from the SES/CEL light and codes that trigger when the engine starts running lean.
If you see this warning light appear or receive the codes on a diagnostic, take immediate action.
Although replacing a DISA valve takes some time compared to other repairs, its risk factors after a failure could destroy the engine.
5. ECU Programming Error
Although this issue is uncommon, it is possible to experience DISA valve failure when the ECU is improperly programmed. This issue occurs most often when the intake gets upgraded on a BMW.
If you suspect this issue is the cause of your symptoms, restore the programming to its original settings first.
Review the valve’s performance from this default mode. Should the problem stop, you know that a different set of standards is necessary to maximize the intake’s performance.
The symptoms may continue after changing the ECU. In that situation, a direct look at the valve, pin, and seal is helpful.
What Are the Repair Options for a Failed DISA Valve?
You have two options available if you suspect DISA valve failure has happened with your BMW engine. The component can be rebuilt by replacing the pin, seal, and flap, or the entire unit can be replaced.
If you hear rattling as the primary symptom from the DISA valve, it may be possible to do a rebuild instead. It depends on how damaged the support components are that support the seal and flap.
When replacing the DISA valve, it is essential to use OE replacements or certified aftermarket products to ensure fitment occurs.
Each engine has different compatibility options to consider. For example, the A-Premium Air Intake Manifold Control Valve replacement offers a direct fit with E46s, but with specific engine codes, from 2003 to 2006.
The YHT Auto Air Intake Manifold Runner Control Valve has different compatibility options, especially when comparing the M54 to the M56 for older BMW vehicles.
If you’re unsure which part is needed for your engine, refer to your owner’s manual for the appropriate code.
Once you have that information, you can review the compatibility of the OE or aftermarket part to see if it will fit as expected.
Replacement Tips for the BMW DISA Valve
BMW installed DISA valves across a broad range of engine types over the decade it was in existence. If you have an M50 family engine in your vehicle, you should be prepared to experience an issue with this component eventually.
What makes the repair tricky is that some of the DISA valves weren’t made the same way.
The first step to take is to determine the valve type you have for your engine. Some drivers can luck out because the replacement part is a simple O ring.
If you have an M52, look for this option, especially if you don’t have any other symptoms of valve failure.
Once you know what you’re up against when replacing this part, you’ll need to consider doing the work yourself or hiring a mechanic for it. If you take the DIY approach, here are the steps to follow to have a successful experience.
- Locate the DISA valve on your BMW engine. It’s typically found on the left of the intake manifold toward the center of the engine.
- You’ll need to remove the air filter housing assembly on most BMW engines to access the DISA valve. Torx fasteners keep it in place.
- Next, you need to disconnect the airflow meter electrical connector.
- Loosen the airflow meter clamp, then unclip the air filter lid clips.
- Once the housing is loose, you can lift the lid out of the engine bay.
- After removing the lid, lift the air filter housing out of the compartment. It helps to lift the rear of it first, detaching the component from the fresh air duct.
- You now have access to the DISA valve. Disconnect the electrical connector by pressing its retainer and pulling off the sensor.
- Remove the Torx DISA valve fasteners, then slide the part out of the intake manifold to remove it.
Once the faulty DISA valve is out, you can replace it with a new one. You’ll follow the removal steps in reverse order to have a successful experience.
The Torx fasteners can be challenging to remove, especially if the heads are stripped. It helps to grind a slot in the head so that you can use a flat screwdriver to finish the work. When that doesn’t help, you may need to carefully drill it out and purchase a replacement of the appropriate size.
How Do I Know If My DISA Valve Failed?
The average DISA valve has a lifespan of 70,000 to 100,000 miles. Drivers that have reached this point with their BMWs should inspect this component often. The seals are typically the first things that stop functioning, creating the dreaded rattling sound that indicates replacement is necessary.
When I was younger, I used to go to different dealerships to test drive vehicles. It was a fun way to get behind the wheel of something exotic and fill the day, especially if there wasn’t something happening on a summer afternoon.
One day, I went to the BMW dealership down the street from my home. The salesperson looked suspicious of me from the start, but took my license anyways, and grabbed the keys.
I took it out on the highway, opened up the accelerator, and the engine started rattling. The salesperson looked mortified. “That’s not supposed to happen,” he said.
I was nonchalant. “What do you mean?” I asked.
He explained the DISA valve and what it is meant to do. Then I was strongly encouraged to return to the dealership to let the mechanics there take a look at the engine.
BMW discontinued the DISA valve because it worked well for your lows and highs, but it didn’t take care of the midrange as successfully. If you get behind the wheel of an older model, you’ll notice that issue immediately.
