Diagnosing a Failing BMW DISA Valve – Sypmtoms, Problems & Repairs

Differenzierte Sauganlage - and because German's can't pronounce this either, BMW just took the first two letters from each word and called this the DISA Valve.

BMW's engineers discovered that the air path through the engine system has an impact on performance. In an effort to improve performance, BMW released the DISA valve in 1995. The valve is responsible for controlling air as it moves through the intake, resulting in improved performance.

First featured in the E39 5-series in 1995, the DISA valve survived until the retirement of the M54 engine in 2006. Across its 11-year life, the valve was used in the M50, M52, and M54 engine which were predominantly used in the E36/E46 3-series, E39/E60 5-series, and a number of the X3, X5, Z3, and Z4 models.

What does a DISA Valve do?

The DISA valve controls the path the air moves through the intake system and into the engine. The valve uses a flap which opens and closes to either shorten or lengthen the path the air takes to get to the cylinder chamber.

At low RPM's, the valve is closed, forcing the air to take the longer path to the cylinders. At high RPM's, the valve opens up which creates a shorter path. Given the path is shorter, there is less space for air. The end result is more pressurized air, which is in turn more combustible.

The ultimate goal of the DISA valve is to optimize performance and fuel efficiency at both low and high RPM's. 

How does the DISA Valve work?

If our short description above wasn't enough for you, read this section.

Prior to entering the engine, intake air flows through the intake manifold. The manifold is what distributes the intake air into the 6 separate cylinders of the engine. When the cylinder valve is in an "open" position, it lets air into the cylinder, and then as the valve "closes" it cuts off air from entering the cylinder. This causes any air flowing in to bounce back off of the valve and back into the manifold. After bouncing backwards off of the valve, it then bounces off the other end, sending the air back towards the valve.

For the most efficient engine performance, you want that air to bounce back towards the valve and reach it at the exact same time the valve is opening again. Because the valves open more slowly at low RPM's, you want this bounce back process to take longer. And at high RPM's you want it to be quicker.

This is where the DISA valve comes into play. At high RPM's it creates less space for air, which creates a faster bounce back. The ECU is responsible for controlling the DISA valve and telling it when to open and close.

Symptoms of BMW DISA Valve Failure

• Poor fuel economy
• Rattling noise coming from the engine
• Loss of power at mid and high RPM's
• Lack of low-end torque
• SES/CEL light and codes for running lean

The most tell-tale sign of a bad valve is a loud rattling noise coming from the intake system. As the seals on the valve wear down, air can slip past the valve in open and closed positions, causing a loud rattle. By this point, you will also start to notice bad performance, lack of power, etc.

The valve is made of plastic and has a metal pin that holds it in place. If the valve or pin breaks, plastic or the metal rod can get sucked into the engine, which will totally wreck your whole engine.

DISA Maintenance & Replacement Options

The DISA valve will normally only last 70,000-100,000 miles. We highly recommend replacing it or rebuilding it at this mileage to prevent any catastrophic failures.

You have two options for repair and replacement:

1. Replace the full DISA unit: if you're valve isn't functioning but you aren't getting any rattle, then you likely need to replace the whole unit.
2. Rebuild the unit: this involves replacing the flap, seal, and pin.

M50 Replacement DISA Unit
M52 Replacement DISA Unit
M54 Replacement DISA Unit

Why was the DISA Valve discontinued?

Ultimately, the DISA valve is effective at low and high RPM's. But it isn't super efficient at mid-range RPM's.

BMW discontinued the DISA valve around 2012 in favor for a more complex intake system which incorporated a second intake "circuit".