944 Sunroof Operation

The sunroofs on 944s are raised and lowered by two lifting arms at the rear edge of the roof. On cars made after February 1986, the lifting arms are operated by plastic gears (one for each lifting arm mechanism). The plastic gears have a small set of teeth which operate the lifting arms. They also have a large set of teeth which are driven by a flexible cable. The cable is driven by the sunroof motor. For cars produced before February 1986, there is a transfer box between the two lifting arm mechanisms. The transfer box has a single gear which moves the lifting arms via two short lengths of drive cable. The guide tubes for the short sections of the flexible drive cable are routed such that the drive cables move the lifting arms directly. The sunroof drive motor assembly is located in the rear hatch area behind the vertical section of carpet on the driver's side of the car. On most cars the motor assembly will have a plastic cover over it which is held in place by six Phillips head screws.

     All sunroofs installed since February 1986 have three limit switches at the motor assembly. Prior to that they had two. On the newer style sunroofs, two of the micro-switches are ganged together and are visible from the front of the assembly. These being out of adjustment are one of the more common problems associated with sunroofs. These style limit switches are fairly reliable. If there is a problem with them, it is more likely they are out of adjustment rather than actually failing. The other limit switch is on the back side of the motor assembly and can't be checked without removing the assembly. On the older style assemblies the two limit switches are located at the end of a rail attached to the back of the motor assembly.

     The two limit switches ganged together will cause a number of problems if they fail or are not properly adjusted. They function together to stop the sunroof in the locked position. The limit switches are numbered with Roman Numerals. The top limit switch is number II and the bottom limit switch is number I. Limit switch III, which is on the back of the assembly near the bottom, stops the sunroof in the fully raised position. The older models do not have the third limit switch. They use a micro-switch between the sunroof visors to tell the system when the roof is in the fully raised position. When the new style sunroofs with the plastic gears were installed, the third limit switch was added to stop the sunroof in the fully raised position. A slip clutch on the cable drive motor stops the roof in the fully retracted position. However, the new style sunroof used a different style slip clutch than the old mechanisms. The micro-switch between the sun visors also performs another function on both models which will be discussed later.

     If the sunroof fails electrically, the sunroof can be raised and lowered manually at the motor. There is a cone shaped dust cover over the adjusting nuts for the slip clutch. By using a socket and ratchet, the nut for the slip clutch can be turned to raise and lower the sunroof. On the earlier models the adjusting screw for the slip clutch must be removed to manually raise and lower the roof.

     On the newer models, the end of the drive cable is attached to a white plastic cam that operates the three limit switches. Limit switches I and II stop the sunroof in the locked (closed) position. If the roof is in the fully raised position (ignition switch in Position 2), as it is lowered (using the down pushbutton), the cam rotates toward the I and II limit switches. The cam is notched such that limit switch I is made first. This stops the roof in the locked (closed) position. From here, with the ignition switch in Position 2, the roof can only be raised. However, if you take the ignition switch to Position 1 the lifting arms can be retracted to remove the sunroof. This is done by depressing the up arrow on the console switch. Yes, I did say the up arrow. The lifting arms move in opposite directions with the ignition switch in Position 1 than in Position 2. As soon as the arms start to retract to the disengaged or released position, limit switch II is made. Limit switch I and II are now both closed. This is what allows the arms to be moved from the retracted to the locked position with the ignition switch in Position 1. If both limit switches are not functioning properly (both closed), the sunroof can not be raised from the retracted position with the ignition switch in Position 1. However, you may be able to take the ignition switch to Position 2 and engage the sunroof using the up arrow on the console button. With the arms retracted and the ignition switch in Position 1, depressing the down arrow will cause the lifting arms to move toward the locked (closed) position. As the lifting arms are moved by the drive cable, the cam on the motor assembly rotates. When limit switch II is released by the cam, the lifting arms stop in the locked position. With the ignition switch in Position 2, depressing the up arrow on the console button will raise the roof until the cam on the motor assembly engages limit switch III to stop the roof in the fully raised position.

     On the old style sunroofs the operation is essentially the same. On difference is that the ignition switch does not have the same number of positions. On these cars the "OFF" position is Position 1 and the "ON" is Position2. Also, there is no cam to operate the limit switches. They are operated by the drive cable as it extends into the track behind the motor.

     The most common problem caused by the limit switches is limit switches I and/or II being out of adjustment. The limit switches can be moved forward and backward to adjust where the lifting arms stop in the locked position. Over a period of time the tabs that the limits switches are mounted to can bend so that the limit switches do not make good enough contact with the cam. As a result, one or both of the limit switches may not be closed when they are supposed to be. This can prevent the arms from stopping in the locked position. It can also prevent the arms from moving to the locked position with the ignition switch in Position 1.

     Another very common problem is related to the plastic gears at the lifting arms. Sometimes these gears get stripped when the lifting arms are moved to the retracted position. I don’t think anyone fully understands why the gears strip. I’ve heard fatigue due to age, uneven loading on the gears when the arms are fully retracted, and the torque on the slip clutch being too high. I personally believe any of these can cause the gears to strip. However, I think the major contributor is the torque on the slip clutch. When I install a new set of gears, I take extra time to ensure that the lifting arms are properly aligned, particularly in relation to each other. I also set the slip clutch torque slightly less than the factory limit. The factory setting is 6 Nm +/- 0.5. I usually set the torque around 5 Nm. This does not affect the ability of the mechanism to raise and lower the roof and provides some additional margin to protect the plastic gears in the lifting arm mechanisms.

     There is one other micro-switch that is important to the operation of the sunroof. It is located underneath the triangle shaped cover between the visors. It tells the system if the sunroof is installed or removed. If the roof is installed, but the lifting arms are retracted for removal, the system will raise the lifting arms to the locked position when the car starts moving. Next to the plastic sunroof gears stripping, this is the single most common failure I’ve seen on 944 sunroofs. When the sunroof fails to move at all in either direction (i.e. the motor will not actuate), failure of this micro-switch is the most likely candidate. A blown sunroof motor fuse or a failed console switch can cause the same indications. There is a small plastic cover which is hinge mounted to the micro-switch mounting plate. The cover must be pried off very gently (the hinges are plastic also) to expose the Phillips head screws underneath. Once the Phillips head screws are removed the mounting plate can be dropped down and the micro-switch exposed. This switch is normally soldered in place. I've seen a number of owners remove this limit switch and jumper the wires

1. The first step in replacing the plastic gears in the late model 944 sunroof is to determine whether one or both of the gears are stripped. If only one of the gears is stripped, it simplifies the replacement process. The gear which has not been stripped can be use as a reference for setting the other lifting arm. First remove the sunroof from the car. If necessary operate the sunroof manually to retract the lifting arms for removal. If you haven't located the motor assembly yet, it is behind the vertical section of carpet in the rear hatch area (behind the hatch compartment light). The carpet is held in place by plastic push plugs. You should be able to slide your fingers behind the carpet and gently pull out to get the plugs out. Your sunroof motor assembly may or may not have a black plastic cover over it. The cover has six Phillips head screws that hold it in place, including one that goes through a rubber grommet and the carpet at the bottom left hand corner of the cover. There is a black plastic cone shaped dust cover on the drive assembly at the base of the motor. Behind the cover, there are three nuts. The outer two nuts are for adjusting the torque for the motor's slip clutch. The large one in back (21mm) can be turned to move the cable/cam. It is also used to check the torque of the sunroof motor’s slip clutch and also how you raise and lower the sunroof if the motor fails. If the nut is rotated in the clockwise direction, it will retract the lifting arms so that the sunroof can be removed. Rotate just enough to get the sunroof out. If one of the gears is still good and the torque on the slip clutch is too high, retracting the lifting arm against the back of the roof may strip the remaining gear.
2. The next step is to disassemble the headliner to get to the lifting arms. There is a cover on the back part of the headliner which is held in place by Phillips head screws. The screws should have plastic covers over them which will have to be pried off to get to the screws. It’s easiest to do this with the back seat down and the rear hatch raised while lying on your back in the luggage compartment. Pull back the weather-stripping along the top edge of the hatch. This will expose the back edge of the headliner which is wrapped around the edge of the body. Gently pull the headliner loose from the body all the way across the edge of the hatch. This will expose the lifting arm mechanisms. If you have the new style lifting assembly, there will be the two lifting arm boxes with a single drive cable guide tube along the bottom of both mechanisms. If there is a box between the two mechanisms with several different guide tubes, you have the old style mechanism. This procedure does not cover the old style mechanism. Carefully remove the lifting arm covers (one at a time) and inspect the gears. Try to keep the gear and the lifting arm from falling out when you remove the cover. If the gear is still good you will be able to use it as a reference for setting the other lifting arm. If one of the gears is good replace the cover. Remove the lifting arm and plastic gear for the ones that are bad. There is a metal washer on the back of the plastic gear which you will need to retain for reinstallation. The grease in the mechanism may cause it to stick in the mechanism housing instead of coming out with the gear.
3. Next, set the sunroof motor assembly so that micro-switch I is made and micro-switch II is not. Here's how you do it. Once the cover is removed you can see the sunroof motor and two of the three limit switches. On the back side of the motor assembly is a white plastic cam that is attached to the end of the cable that operates the lifting arms. As the motor drives the cable, the cam rotates and hits the different micro-switches to stop the lifting arms. The sunroof motor is mounted on its side and has a round drive assembly at one end. With the ignition switch in position 2 and the sunroof installed, depress the up arrow on the console switch until the motor stops. Then depress the down arrow on the console switch until the motor stop. At the motor assembly, there are two micro-switches above the motor. There is a small opening behind the micro-switches that you can see through. If the cam is set properly, you should be able to see the white plastic cam hitting the arm on the bottom micro-switch (should be labeled I). The cam should not have hit the arm on the other micro-switch (labeled II yet). If you are unsure if it is properly set, you can adjust it manually and listen for the micro-switch to click. If you turn the nut counterclockwise the cam will rotate toward the left away from the micro-switch arms. This is just like raising the sunroof. Turn it counter clockwise enough so that you're sure the cam is not hitting the micro-switch. Then turn it back clockwise until it hits the bottom micro-switch arm. You should hear it click. While you're at it, you may want to rotate the cam far enough clockwise to hear micro-switch II click. This isn't a guarantee that both micro-switches are working electrically, but it does verify that they are working mechanically. Once you've done this, set the cam back to where that just micro-switch I (bottom) is made. This is the correct position for the sunroof in the locked position. The reason for verifying that both micro-switch switches click is that the micro-switch mounting assembly sometimes bends so that the cam will not make the micro-switches. If this happen you will have to remove the micro-switches and bend the mounting arm slightly so that the cam will make the micro-switches.
4. The next thing to do is to mark the lifting arms for installation. If you look at the tracks on the sunroof that the lifting arms slide in to, you’ll see a sharp bend almost like a knee. The middle of the curve of the knee is where the round peg on the lifting arm sits when the roof is in the locked position. With the roof installed and closed, lay one of the lifting arms in the track in the lifting element where in normally sits. The lifting element is the box that the lifting arm and the plastic gear sit in. Don’t install the gear yet. Slide the element up into the track in the roof until the round peg is in the middle of the knee in the track. Put a mark on the lifting arm where it is lined up with the edge of the lifting element. Bright finger nail polish works well. Remove the lifting arm and mark the other lifting arm in the same spot. You can measure using a ruler, count the teeth on the lifting arm, or hold them side by side to figure out where to mark the other gear.
5. Before installing the gears, we need to check the torque on the slip clutch. Using a 21mm socket and a torque wrench turn the nut large nut at the motor that manually raises and lowers the roof. The slip clutch is what actually allows you to raise and lower the roof without turning the motor. As soon as the 21mm nut starts to turn, that is the torque you are looking to check. It should be 6 +/- 0.5 Nm. This is a very low torque. You may have to borrow a torque wrench of this range if you don’t have one. I usually set mine a little lower than the factory spec (around 5 Nm). I think it helps protect the gears.
6. Now we’re ready to install the gears. Remove the sunroof from the car. There should have been a thin metal washer on the back of the old gears. If it is not there it is probably still in the lifting element body. Make sure you put this washer on the back of the new gear before installing. Lubricate the gear with grease before installing. Porsche calls for a special grease (TL-VW 745 Universal Cold Grease). It should be available at the Porsche or Volkswagen dealer. I’ve never bought the special grease. I just use a good quality, fairly heavy grease. You don’t need to apply an excessive amount. Install the gear in the lifting element housing. Insert the lifting arm so the mark on the lifting arm lines up with the edge of the housing (as we had previously measured). Screw the cover in place. Repeat for the other side.
7. With the ignition key in position 1, carefully bump the up arrow on the console switch and watch the lifting arms. They should retract toward the lifting element housing as if you were going to remove the sunroof from the car. Be VERY careful here. Make sure that as you bump the lifting arms toward the retracted position, the round pegs on the lifting arms reach the element housing at the same time. When the pegs hit the housing, it acts as a mechanical stop. Due to uneven loading, the gears will strip if the arms do not hit the mechanical stop at the same time.
8. Once you’re sure everything is aligned and working correctly, install the sunroof and you’re ready to go. I try to made sure the lifting arms are set perfectly and that the torque for the slip clutch is a little low. My gears have been in for about a year and have not stripped yet. And I remove my roof a lot in the summer time. When I first started working on sunroofs, I stripped several sets of gears while trying to get the arms set correctly. However, this was also before I knew how to check the torque on the slip clutch. That’s why I told you to order two sets of gears. It’s just a little insurance. I always like to keep a spare set of gears handy anyway.
9. If you find that the roof doesn't lock down tight enough (i.e. the pegs on the arms aren't hitting the right part of the knee in the track) you can adjust this by moving the two micro-switches forward or backward. If you move them forward, the arm will stop more toward the released position. If you move them forward, they will stop more toward the raised position.