Hello – for those of you who are curious and have access to VCDS (Vagcom). This test takes 20 minutes tops and it is well worth your time. If you don't have VCDS, I suggest you check out the Ross-Tech website and invest in VCDS...your RS4 will thank you for it.
The function test needs to be done shortly after the car has been running. Several of the tests require vacuum reserve, including the flap tests. There are other criteria, but VCDS does not explain what they are. You may get a message stating “Requirements for Output Test not Met”. You will also get this message if you abort the Output test and then try to start over. Read these steps so that you know what to expect and don’t have to start over. But in the event you need to try it again, just close VCDS, start the engine and let it idle for a while, turn it off and then try the Output test again.
PHOTO 1 – Remove the inlet snorkel that goes from the grill area to the top of the airbox. There are (2) screws that secure the front of it and the rear portion just snaps into the airbox. The snorkel is made up of two parts, but it shouldn’t have to be separated to remove or install. There is also a small screen where the snorkel snaps into the airbox (on US models anyway).
PHOTO 2 – If you are doing this test by yourself, position the laptop close to the engine so that you can easily monitor the flaps once you start the test.
PHOTO 3 – The yellow arrow is pointing at the Power Flap inside the airbox. It is easily visible with a good flashlight. There is another photo of what the power flap inside the airbox (filter box) looks like a few posts down.
PHOTO 4 – The white arrow is pointing at the white plastic arm that rotates the Intake manifold shaft on this particular side of the manifold. There is an identical white arm on the opposite side of the manifold that will also rotate during the test.
From VCDS Main screen:
- Click on “Select” button to go to the control module list
- Click on the “01- Engine” module
- Click on “Output Tests -03”
- There are several operational tests that can now be performed, they are done in a sequential order, and the ones you are not concerned with can’t be skipped. Luckily, there are only (2) other tests prior to the ones we care about. There are several other tests after the flap tests, but you can cancel out of the testing at that time. The first test is “Voltage supply relay”. To start the test, click the “activate” button. You will hear a clicking sound as the relay is checked. To stop the test quickly, click the same button again. The second test is “Signal line for fuel pump”. Again, click the activate button twice quickly to start and stop the test. The third test is now “Intake Air Switch Over Valve”. The test will tell the ECM to activate the vacuum-operated solenoid that opens and closes the power flap in the airbox, just upstream of the air filter.
- Be sure you are in position with a light to watch the flap (Photo 3). Click the activate button. The solenoid will start cycling the valve. I suggest you only let it cycle 2-3 times so that there is sufficient vacuum reserve left for the Manifold Flap test. Click the button again to stop the test.
- The next test is “Intake Manifold bank 1”. It actually tests both banks because the solenoid being checked (the Intake manifold runner control valve) operates 2 diaphragms, one for each bank. There is a picture below that shows the underside of the manifold.
- The easiest part of the runner flap movement to see is the white, plastic arms that are being rotated by the diaphragms (Photo 4). Click activate and the solenoid will start cycling the flaps. Try to view both white plastic arms as they move. Click again to stop the test.
-If you'd like to check the operation of the OEM muffler flaps, click the activate button quickly to progress through the outputs tests until you get to the Exhaust Flap check. Press Activate again and the exhaust flap solenoid will begin to cycle open and closed. If you quickly walk towards the back of the car, you should hear the flaps opening and closing. By this point in the testing, you may be getting low on vacuum reserve and the flaps may only open/close a few times. Click again to stop the test.
- Click “Done” to cancel the Output testing.
Notes on what you’ve just tested:
If the operational checks show that the ECM can successfully operate the flaps during the tests, you can be quite sure that the ECM operates them successfully while the car is being driven. It’s the same signal. An Intake Manifold Flap problem should definitely cause a CEL since there are sensors that monitor whether they are opening and closing as commanded. The position of the Manifold flaps can be logged with VCDS using the Advanced Measuring Value feature. The blocks of interest are in Group 142 and you can log both specified and actual values. The specified values are either 0% (tumble position) or 99.6% (no tumble position). The specified and actual values of the Exhaust Flap position can be logged as well. They are in Group 79 and the values are either ON or OFF. The position of the Power flap in the airbox is not monitored with a sensor. Hence, there is no variable you can log with VCDS to see what it's doing in real time (that I know of). Depending on ambient conditions, the RS4 usually exhibits a noticeable increase in power at around 5500-6000 RPM. When the airbox power flap opens at 5000 rpm, the intake sound of the engine should become slightly louder and more raspy. The opening of the flap is NOT responsible for the power increase, it just accommodates the increased airflow demand that coincides with the power increase. If you do hear the intake sound change at around 5000 rpm under full throttle, the airbox power flap is probably working fine.
Known issues (rare, but they have happened):
The RS4 vacuum system is not very complicated, but the same network of vacuum lines controls all the flaps discussed. The testing procedure and info in this post should help determine if an issue exists.
1) There have been instances where the vacuum hose feeding the airbox flap is pinched during vehicle assembly at the factory. This renders the airbox flap non-operative, but doesn't affect the other flap systems.
2) The airbox power flap is a plastic flap that turns about 90 degrees in a plastic housing it has been known to stick either fully open, fully closed or at some position in between. So the vacuum lines are intact, but the flap doesn't physically rotate as it should. No affects on the other flap systems, but see related intake air temperature issues in Issue 3 below. Sometimes some emery cloth on the flap perimeter and housing bore is all it takes to get the flap to move as it should.
3) Some RS4 owners are so enamored with the raspy, aggressive intake sound that the airbox power flap creates, they decide to remove the flap altogether. This may change the intake sound at lower RPMs, but now the engine is sucking in very hot engine compartment air ALL the time. Audi engineers designed the flap to open at high road/engine speeds for a reason - because there is sufficient air movement thru the engine compartment to ensure the air entering the open flap is relatively cool. The RS4 is extremely sensitive to inlet air temperature (IAT). Power will drop and ignition timing will be overly retarded if the IAT becomes high. The same goes for Issue 2 with a flap that is stuck open - the IAT will be elevated and engine output will suffer.
4) RS4 owners replace their mufflers with aftermarket mufflers that are not equipped with the vacuum operated valves. This is fine as long as the vacuum line going to each valve is plugged. If they are not plugged, there will be a vacuum leak in the entire flap system every time the exhaust solenoids are commanded to open. This gets difficult to trace since the command depends on RPM, Sport Mode on/off, and even road speed. The biggest problem is the intake manifold tumble flaps require vacuum to maintain their commanded 'Open' position at higher RPMs. If the exhaust valve hose(s) are compromised (not plugged), the resulting vacuum leak will probably cause the manifold tumble flaps to surely start to move back to their tumble (Closed) position, which will cause a dramatic power loss since airflow into the engine will be greatly impeded by the closed tumble flaps.
5) Cases of unusually high amounts of carbon buildup in the intake valve area can create buildup around the intake tumble flaps. If excessive, the flaps may not be able to move their full range. This should throw a CEL (tumble flap implausible signal) as well as a EPC light. See your dealer. If you want to check the tumble flap positions yourself with VCDS, the blocks of interest are in Group 142 and you can log both specified and actual values. The specified values are either 0% (tumble position- Closed) or 99.6% (no tumble position - Open). The flaps are normally commanded to be Open at engine speeds higher than 2500 rpm, so vary the engine speed while you do the log. If your actual positions are more than 10% different than the specified position, chances are that is the reason for the implausible signal CEL.
6) One of the tumble flap position sensors simply goes bad. This should throw a CEL (tumble flap implausible signal) as well as a EPC light even though the vacuum system and flaps are functioning fine. See your dealer. You can also log what the actual and specified flap positions are as explained above in Issue 5.
Happy testing!
