(As of 10-25-2019 I have plenty of repair parts available.)
If you're here then you're probably having a problem with the pneumatic central locking system in your Audi A3, A4, S4, A8, or S8. This website is a collection of information about troubleshooting and fixing the problems associated with this system. If your car has a central locking control module with the part number 8L0862257N 8D0862257N 8L0862257B or 8D0862257B, or any other module starting with the part numbers 8L0862257 or 8D0862257, then this information will apply to your car.
In general, the following US-spec cars use this system (cars in other markets may vary somewhat):
Audi A3 1996 - 2003
Audi A4 1997 - 2001
Audi S4 2001 - 2002
Audi A8 1997 - 2003
Audi S8 2001 - 2003
Audi A6 1997
Audi A6 1998 (Avant only)
Description of the System
The heart of the system is the central locking pump control module (CLP) located in the
trunk. It's in the right rear corner of the A4 & S4, and in the left rear corner of the A8 & S8.
The CLP consists of a graphite rotary-vane pump driven by an electric motor that generates
air pressure or vacuum that locks and unlocks the doors, trunk, & fuel door. The air pressure
& vacuum are distributed through a simple network of plastic tubing. The CLP also contains
some circuit boards & chips that are responsible for interfacing with the remotes, controlling
the security system, controlling interior lighting, and several other functions.
The Audi pneumatic central locking system is plagued by several common problems as it ages.
The most common problem is when the internal graphite parts of the air pump wear out and shatter. This is the result of normal use and wear of this component. Many owners have observed the locks taking longer and longer to unlock over a period of weeks or months as the pump parts are in their final stages of life.
Another problem is failure of the electronics due to water intrusion into the trunk. In extreme cases the electronics failure can cause the CLP to run until it heats up and melts. Water intrusion on the A4 & S4 models is often through a faulty trunk seal or faulty right side tail light seal. Water intrusion on the 1997 - 1999 A8 is often through the fender-mounted radio antenna, which is directly above the CLP.
A third type of problem involves failures or leaks in the network of plastic tubing that connects the CLP to each of the locks it controls. The most common leak is in the hinge area between the body and the driver's door. The hard plastic tubing in this area becomes brittle with age and repeated flexing as the door is cycled; it can break here and cause a leak. Leaks at the trunk/hatch lock actuator are also fairly common. Leaks can occur in other parts of the system; more information on leaks is included in the troubleshooting section below.
The first step in troubleshooting is to determine if one of the common problems described above is your problem. Use the flowchart to work through the process. The text below roughly follows the flowchart and includes a few additional details. You can click on many of the photos for a much larger view.
Open all the doors operate the key in the drivers door lock a few times to lock & unlock the doors. Observe the lock knobs on each door. If any of them fail to move at all then you either have a leak in the system or an air pump that is failing. Listen for any hissing, which would indicate a leak in the tubing system. Locate the source of any hissing and patch any breaks using standard rubber or silicone vacuum line.
Assuming your remote has been working well prior to the CLP problems, i.e. the batteries in your remote are good and the remote is synched to the CLP. Push the lock & unlock buttons a few times with a few seconds in between. Observe the side marker lights and listen for the alarm horn to honk. If those lights flash and/or the horn honks when the alarm is arming the same way they did before the CLP problem then it's a safe bet that your electronics are OK and the problem lies elsewhere.
Place your key in the drivers door lock and lock & unlock the door a few times. If the alarm horn honks when you lock the door then the electronics in the CLP are probably OK. Next, open the trunk and listen for the sound of an electric motor near the right rear (A4) or left rear (A8) corner of the trunk while operating the key in the drivers door (or trunk lock). If you hear the motor running for 5 to 15 seconds then the electronics in the CLP are probably OK.
Next, you'll need to locate the CLP in the trunk and assess it's condition. It is exposed by removing a little bit of hard plastic trim along the bottom edge of the trunk opening and gently pulling the hard molded 'carpeting' out of the way. The pump is housed in a dense foam rubber block that's probably designed to reduce the noise of the pump when it runs. If the foam block is wet or damp then that's a good indication you have water intrusion into that area of the trunk that has (or will) fried the electronics in your CLP.
Remove the pump and foam block from the area it's mounted in. Be VERY careful not to stress
the connection between the 2 vacuum lines and the CLP. The nipples on the CLP can break if
abused. I prefer to remove some of the wire ties holding the wiring harness to the body of the
car to give myself more room to work. With the CLP in a reasonably handy & stable spot,
gently remove the 2 vacuum lines by pinching the outer ring with your fingers while pulling the
connectors straight off. The photo at the left shows you how the connection is designed.
Pinching the outer ring in the right spots (as marked by the yellow arrows in my photo) moves
the locking tabs out and away from the barbs on the nipple.
CLICK ON THE PHOTO FOR A LARGER VIEW.
With the CLP exposed, the vacuum lines removed, and the electrical connectors still connected you can do a few more tests. Push the buttons on your remote or lock & unlock the doors with your key and observe the CLP. You might be able to hear it hum as the electric motor inside runs. Place fingers over each vacuum nipple and operate the locks again, observing whether or not you can feel any air pressure or vacuum generated.
If the electric motor runs and you can't detect air pressure or vacuum then the rotary vane pump inside the CLP is probably broken. More on that below.
If the CLP seems to generate pressure and vacuum then you may have a leak in the tubing network. Place one of the vacuum lines with the white connectors into your mouth and seal your lips around it. With minimal effort you should be able to lock and unlock the doors while blowing and sucking on the lines. The smaller line controls the drivers door and the fuel flap door. The larger line controls the other 3 doors and the trunk/hatch. If the door locks don't respond then you probably have a leak in the system. If they do respond to your breath test then the CLP probably isn't generating enough pressure & vacuum.
At this point you should have a good idea of which type of problem your particular CLP is experiencing. If you get any noise at all out of the pump while turning the key in the door lock then the electronics are probably OK. If you can operate the locks with your breath then the tubing network to the doors is probably OK. If the foam block is wet and the CLP doesn't respond to the remote or the key in the door lock then the electronics in the CLP are probably fried.
If you suspect the graphite rotary vane air pump inside the CLP then you'll want to dig just a little bit deeper. Remove the 3 electrical connectors from the CLP and take the CLP to a stable place to work on it. Remove the white lid by gently prying it off of the 8 locking tabs holding it on. Set the lid aside and inspect the circuit board. When the graphite pump fails it usually distributes a messy black film of carbon dust all over the inside of the CLP. It will probably be all over your fingers at this point if that's the case. Also inspect the circuit board for any mineral deposits, corrosion, or other indication of long term exposure to moisture. Remove the circuit board by gently pushing on the prongs of the electrical connectors with your fingers. The board should easily pop out with very soft pressure from your fingers. The board will still be connected to the CLP by a ribbon connecter. I generally set the pump on its side and allow the circuit board to lie flat on the table. Again, watch for the black dust and inspect the bottom side of the circuit board for moisture issues.
The last step in troubleshooting the CLP is to remove the 3 brass-colored screws from the
round top of the black graphite rotary vane air pump and assess the internal components.
I like to mark the orientation of the parts by marking them down the side with a paint stick
before removing the screws. I also set the pump upright and allow the circuit board to sit
on top of the housing (see photo), being VERY gentle with the cable.
CLICK ON THE PHOTOS FOR A LARGER VIEW.
When you remove the 3 screws and the top of the pump you'll probably see dozens of broken black graphite parts and the source of all the black dust. If so, then the pump itself is obviously broken. See the Solutions section for a source of parts to fix this particular fault.