back to 1000q: 2004 2005 VW Passat TDI "how to" index
The CCM module has a part in: window/sunroof control, door locks, alarm, keyless entry, engine start, interior lighting.
The problem is that if water soaks the interior from an open window, clogged sunroof drain (see 1000q: clean sunroof drain to prevent this), or other water leak, it can damage the CCM. Be particularly careful on the driver side drain for the CCM and the passenger side drain for the automatic transmission computer. Although there is a gasket around the wires, the CCM is located in a low spot where water will pool. If you pull up the carpet and you see a puddle of water, be prepared to buy a new CCM.
VW actually had a recall where they gave you an extra sheet for the owners manual that said to check the drains. They might have also opened up the drains a little. If you paid for repairs in the past they would reimburse you. I do not believe this applies to future repairs since they change the owner's manual service recommendations.
Avoid leaving a big pile of snow in the footwells to melt into the carpet. Close your windows and sunroof when it's raining. While the location of these modules is really dumb, you can't control it - you can control leaving the windows open. In addition to cleaning the sunroof drains as shown above, also make sure the drain under the battery tray is flowing properly and clean out all the leaves and gunk under the windshield cowl - pull up the plastic cover and pull out any stuff there. Then flush it with water. There are gaskets around the ECU box and cabin air filter, make sure they are seated and leak proof.
If your VCDS cable cannot connect to the CCM try unplugging it and then replug it in.
Some functions that can be adjusted by the CCM: doors autolock above 15 mph, doors autounlock when the key is removed from the ignition switch, or all doors unlock when you press the unlock key on the key fob instead of 1st press unlock driver's door, 2nd press unlock all doors.
NOTE - if changing the CCM, you need the correct part number and I believe you also need to match the bar code printed on it for model type and programming.
If you wish to retrofit power seats to your Volkswagen Passat, see 1000q: power seat swap for details and tips.
torx and screwdriver
13mm wrench or T45 bit
Disconnect the battery. Loosen the 10mm nut on the negative terminal and then remove the negative terminal. Place an insulator between the terminal and battery so that they can't touch. Before touching any side airbag plugs or wires, always touch an unpainted bare metal ground like the door striker pin to discharge static electricity on your body. It's possible for a static discharge from your touch to activate the side airbags! Also step on the brake pedal to try to turn on the brake lights and discharge any stored electricity in the system.
Move the seat all the way forward. Use a pick to remove the 2 round trim
plugs shown below. Remove the torx or phillips screw (changed over the
years) and pull the plastic trim covers off.
Remove the 2x 13mm nuts on the front of the seal rail. Some model years
have 2x T45 torx screws instead. Slide the seat all the way back.
The seat will come off the rail but it will still be held down by the wire harnesses.
Here is the seat removed with arrows pointing to the 13mm nut studs.
Some seats may use torx bolts.
CAUTION - touch the door striker (the bare metal knob that the door latch touches) or another bare metal ground on the car to discharge static electricity! Static discharge could while touching the airbag plugs could result in airbag discharge and damage to persons or property!
Unclip the wire harnesses. The white plug has a tab in the middle, pry
it up to release it from the white plastic arm in the pic below (yellow
The side airbag plug (large yellow clip) has to be released by pulling up on its cover as
shown below by the screwdriver.
Once the wires are released, slide the seat back and it will come out. The passenger seat
is the same. Here is a picture showing the seat rail gap.
Remove the floor mat. Pry off the screw cap on the side panel shown
below. Remove the screw or nut there. Remove the nut on the dead pedal
(the large non functional foot rest on the left) and remove it.
Pry up the door sill trim. You only have to pull it up to the B pillar,
the center pillar on the car, aka the seat belt area. The yellow arrow
below shows the metal clasp that must be released before pulling it out.
Feel under the carpeting and remove the black box under the driver's side
footwell (CCM). If you are removing the automatic transmission control
module, you do the same thing but under the passenger seat.
Pull out the box - there is a ground wire which will limit how far you can pull it out. You can remove it if you need more room.
Open the box and unplug the CCM. If there's water inside the box you may need a new CCM. If you see green corrosion around the wiring you need to fix the wires before reinstalling any new electronics.
Installation is the reverse of removal - note the gasket on the box when reinstalling the CCM. There is gasketmaker around the wire harness on the CCM but water could still leak in. You can add some gasketmaker as cheap insurance against water leaks - or just remember to close your windows. Do you have more notes on CCM problems? Comment in the VW TDI forum or search below for more help.