Cleaning Your Boxster Drains

It is critical to ensure that you know about Cleaning Your Boxster Drains. This needs to be done as a regular maintenance item.

Having read various stories of blocked drain holes causing floods and very expensive repairs I put this article together.

If your car ever experiences wet floors in the cabin, you need to ensure your drains are clear to prevent damaging your immobilizer or CLU (Central Locking Unit.)

What is a CLU?

The CLU is a computer that can only be programmed once (EEPROM).  It stores the security codes for each one of the keyless entry remotes as well as the security codes for each of your keys’ immobilizer “pills”. This is a critical device for the operation of your Boxster.

Cleaning Your Boxster Drains will save your Central Locking Unit "CLU"
Central Locking Unit “CLU”

The Immobilizer (CLU) is very well protected. Unfortunately, Porsche located the CLU in the lowest point of the passenger cabin under the left seat.  As a result, if ANY water gets into the cabin, it will pool and hit the CLU first. This could happen from a window or convertible top left open during a rainstorm or from clogged drains.  This post will deal with preventing clogged drains and thus saving your CLU from any damage.

If your cabin floods with water, DO NOT put the key in the ignition or try to operate any electrical components in your car.

A damaged immobilizer (or CLU) is a VERY costly repair that is totally preventable through normal maintenance of cleaning your drains.

Cleaning your drains is a small maintenance item. This maintenance has minimal to no cost (just labor), and it will save you a lot of money in potential repairs.

Where are Your Boxster Drains?

Boxster Drains locations for Cleaning Your Boxster Drains
Figure 1: Boxsters 1997 – 2012 Have 4 to 6 Drain Holes.

It is strongly recommended that you regularly clean your drains. You need to clean/clear drains 1 and 2 (from figure 1 above). Drain 4 is under the battery and should also be considered.

Cleaning Your Boxster Drains

  1. Move your Boxster convertible top into the “maintenance mode” or “service position”.

How to Move Your Boxster convertible top into the “maintenance mode”

Ben Burner shows you all the steps to get your Boxster’s convertible top into “maintenance mode”.

Open convertible top to approximately halfway point as if you were going to remove the engine cover, BUT you are not going to remove the engine cover.

I have linked to a Ben Burner video (above) that shows you all the steps to get your Boxster’s convertible top into “maintenance mode”.

You merely need to do the steps on the convertible top positioning and securing the canvas top into a position to provide you access to the drain screens. You only need to do the work until the 1:50 mark of the video (above), do not remove the clam-shell or the engine cover. These steps are not needed.

Remove Key

  1. Once your convertible top is in “maintenance mode”, remove the car key to prevent any movement of the convertible top.
Boxster Drain Screen and your primary target for Cleaning Your Boxster Drains
987.2 Boxster Drain Screen

Inspect Your Drains

  1. Inspect your drain screens (left and right under your clam-shell (items 1 and 2 in figure 1) and clear ALL debris collecting in the area. It is clear from the photo above that this 987.2 Boxster has been collecting water and that it needs servicing (a good cleaning at the very least.)

    If your drain screens (Porsche Calls them Water Drip Pans) are missing (or not included) it is recommended that you install them on a priority. Your local Porsche Dealer Parts Counter can easily provide these low-cost parts.

Clean Drain Hole Areas

  1. Clean the area around the screens (or drain holes) thoroughly. You can vacuum and wash the area initially.

Remove Protective Drain Screens

  1. Remove the screens by pulling the drain screens straight up (the screens simply pop-out.)

Diagnose Water Leak Issues

  1. As far as diagnosing any water leak problems, fill a quart jar with water and put a pan on the ground just forward of each rear wheel to catch the water as you pour it down each drain hole. 

    Some people use hot water.

    The drains exit just forward of the rear wheels. Check to confirm that you have a full quart of water after it all drains out.

Inspect Drain Areas for Any Damage

  1. Be sure to check each foam (or plastic) liner drain tray area for any rips or tears, especially in the area directly beneath the V-levers that operate the pushrods of the convertible top. 

    If you ever had one of those pushrods break and the V-lever rotated with the broken pushrod dangling, it will invariably cause a tear in the drain tray area that will in turn cause water to leak into the passenger compartment.

Determine if Drains are Clogged

  1. If the water is slow to drain then your drains may have collected debris. See How to Remove Debris from your Convertible Top Drains (below)

Replace/Install Drain Screens

  1. Replace the screens and you are finished. Good Job!

How to Remove Debris When Cleaning Your Boxster Drains

The best way for Cleaning Your Boxster Drains that are slow to drain water from your clam-shell compartment is to use a Trombone Flex Brush. You can source this brush from eBay or Amazon for under $8 USD.

TromBone Brush
Trombone Brush from eBay

Simply push the brush through the hole(s) until it comes out the bottom of your car. Easy Peasy!

Check for Water Collection on the Tank Tray

You should never experience water collection below your gas cap in the gas cap compartment. Drain 3 (in Figure 1) is behind the gas flap and if it becomes clogged, then you will see rainwater collecting around your gas cap.

Gas Cap Compartment: Drain Hole is clearly visible
Gas Cap Compartment: Drain Hole is clearly visible

It is very unlikely, but always be on the lookout for any rainwater collection below the gas cap in the gas cap compartment of your Boxster. If this happens somehow your drain hose (number 3 in Figure 1 above) has become clogged.

Beware of a Wet Cabin Floor!

You need to be VERY careful to detect any water that is ending up under your seats. Correct the problem with any of the rear drains ASAP.

If you normally park your car outside you run a high risk of having your drains become clogged and thus flooding the interior of your car.

When your drains (1 and 2 from the figure 1 above) become clogged, all water collected in the area of your convertible area (under the clam-shell) will re route to the interior of your cabin.

Failure to clean your drains can result in a wet immobilizer (CLU) under the left cabin seat, which will cost up to $3600 USD to repair.

 wet immobilizer under the driver's seat = $3600 repair
 Wet Immobiliser under the Left Seat can Easily Result in a $3600 USD repair

How do you Remove Water from Your Boxster floor?

Act quickly when you encounter water on any Boxster floor. Use a wet and dry shop vac, or apply towels/rags to remove as much water and moisture as possible. DO not start the car. Check your ECU that it is not wet. Open car doors remove all carpets or mats and setup fan(s) to blow through your car in an attempt to remove all moisture (please note fans can take up to 3 days.) You need to remove all the moisture before the mildew sets in.

Symptoms of a Failed Immobilizer (or CLU)

Common malfunctions when the immobilizer gets water-damaged:

  • Engine won’t crank or start
  • Windows go up or down on their own
  • Alarm horn goes off
  • The convertible top becomes inoperable
  • Interior lights stop working
  • Airbag light will come on
  • Turning signal lights won’t work
  • Remotes will not work
  • Doors can not be locked or unlocked
  • Both front and back trunks do not open or close
  • No communication to the DME ECU
  • The radio will not work
  • Can not open the fuel tank cap

What to Do If You Suspect a Wet Immobilizer?

If you detect a wet cabin floor, you need to act swiftly. You can sometimes resurrect your immobilizer by opening it up and drying it out. However, it is much better to prevent it from happening in the first place by Cleaning Your Boxster Drains. If you see that your interior cabin is wet you need to unplug the battery and get fans and/or a hairdryer to dry the area off, and then see if things work again. 

You may have to remove the seats and clean the immobilizer controller with isopropanol alcohol.

Removing the seat is a very simple matter.  There are four Torx bolts holding down each seat, but you can get them off with a 10mm small drive (1/4 inch) regular socket if you are careful.

To take the seat completely out, you will have to disconnect the large connector under the seat. 

DO NOT disconnect seat connector with the ignition on or turn the ignition on while the seat connector is disconnected or you will set off your airbag light.

The airbag light can then only be reset with a PST2, PIWIS, or Durametric unit.  It is possible to set the seat on the ground next to the car without disconnecting the connector, but the seat does get in the way. If you go that route, you don’t have to worry about the airbag light.

What to Do with a DEAD Immobilizer (CLU)

You will need to research the many web posts online on how to deal with this issue. If you are highly skilled, you may be able to fix this on your own. Otherwise, you will need to make use of a local service or from the internet (such as ECUDoctors.)

I recommend that you reach out to any/all PCA members (this is a common issue) that most members are aware of. Failing that, you will need to research the Boxster Web Forums.

Online you can search for a number of Immobilizer (CLU) repair specialists. The repair of this issue has become a dedicated industry on its own.


Cleaning Your Boxster Drains is a very simple regular maintenance item that will save you the horrible experience of a drowned CLU and save you the costs of repairs.

How to Water Proof Your Immobilizer (CLU) Box

There are now a number of 3rd party manufacturers who are selling waterproof solutions for your immobilizer (CLU) box. I have not tested any of these solutions, but wanted to let you know that these solutions are prevalent on eBay, Amazon, and other direct ECU/CLU repair companies specifically for Boxsters.

From the Internet:

Excellent Video from Aaron Sorgius

Other Articles of Interest:

Why would the floor of my car be wet?

There are a couple of possibilities for the cause of wet carpet. It can be caused by a perished door membrane, but the primary reason is usually that dirt and leaves are blocking the rear roof drains and as a result forcing rainwater into the cabin. The water almost always collects under the passenger seat, which can make it difficult to spot.

How do you remove water from the car floor?

Act quickly when you encounter water on the car floor. Use a wet and dry shop vac, or apply towels/rags to remove as much water as possible. DO not start the car. Check your ECU that it is not wet. Open car doors remove all carpets or mats and setup fan(s) to blow through your car in an attempt to remove all moisture (please note fans can take up to 3 days.) You need to remove all the moisture before the mildew sets in.

One thought on “Cleaning Your Boxster Drains

  1. I have a 2003 Boxster S.
    Your video on cleaning the drain holes was very informative and I have checked all of mine. I have found one extra drain hole that was not shown on your videos. It is located under the front truck area. There are two drain holes on the driver side and one drain hole on the passenger side. I can email you a photo if you wish to see the location of the two drain holes on the driver side.

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