On The Road

Searching for a vacuum leak in a 2011 Audi A4 2.0 turbo

We had a customer come to the shop recently with a check-engine light on in his 2011 Audi A4 2.0 turbo. The customer said the car was running a little rough when the warning light went on.

After checking in the car and scanning it, we pulled a P2187 fault code (bank 1 system to lean at idle) from the engine control module. Lean codes are common on Audis, so it was time for us to look for a vacuum leak.

When looking for a vacuum leak on a late-model 2.0 turbo Audi or Volkswagen, always start by checking the oil-filler cap. Before I explain why, let me describe what the Positive Crankcase Ventilation (PCV) system does.

The average gasoline piston needs to have approximately 140 to 200 pounds per square inch (PSI) to operate normally. During the combustion cycle, a small amount of the pressure will escape into the crankcase (engine oil pan area under the pistons). It could be approximately 1 to 4 PSI. Because the engine is sealed, if that small amount of crankcase pressure is not released, it will start to damage the engine or pop the engine seals out. In the early days of autos, there was a pipe off the side of the engine block that vented oil, unburned fuel (hydrocarbons) and sludge into the environment.

During the 1950s, environmentalists and researchers from the state of California began to realize that automobiles were the cause of the growing smog problem. After further studies, they realized that crankcase blow by gases was the cause of half of the measured hydrocarbons. The results drove the automobile manufacturers to solve the growing auto emissions problem.

By the 1960s, the manufacturers figured out that if they used the intake manifold vacuum, they could vent the crankcase of harmful and toxic gases. All manufactures do it a bit differently, but it is still the same basic system in the end. There is a hose or valve at the valve cover that has plumbing that runs back to the intake manifold. Once the engine is running, the intake manifold vacuums and vents the unburned fuel and other gases from the crankcase. Once these gases get to the intake, they can be reprocessed back through the engine.

Testing the Audi

The Audi in this case uses an elaborate oil separator valve (PCV valve) that is bolted directly to the valve cover. Because this system vents the crankcase, it can also pull up oil solids.

The Audi system is designed to separate the oil solids from the gases. It does this with the use of a rubber diaphragm built into the oil separator. Over time, the diaphragm can break or rip because of the harmful gases and solids. Once the diaphragm rips, it causes a massive internal vacuum leak that prompts the air fuel ratio to go lean. It also stresses all the seals in the engine, especially the rear main engine seal. It does this because of the vacuum coming straight from the intake manifold. One can test this by trying to remove the oil filler cap while the engine is idling. If the cap comes off easily, the separator is OK; if you have to pull really hard, the diaphragm is ripped.

The important thing to remember is that even if you do the oil cap test, you still have to perform a full vacuum test. Usually, there is more than one vacuum leak.

This Audi needed the latest oil separator and an engine control module update to go along with the new separator. It’s important to get the latest oil separator from Audi because there have been so many revisions.

Engines are getting cleaner, more efficient and more powerful, yet despite all of this new technology, gasoline engines still have a long way to go.

Matt Pataky owns Sunnyvale Foreign Car Service, 15 Pioneer Way, Mountain View. For more information, call 960-6988, email This email address is being protected from spambots. You need JavaScript enabled to view it. or visit sunnyvaleforeigncar.com.

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