DIY cabin air filter and ECU removal and replacement.

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Difficulty: 1/5


This procedure shows how to replace the air filter or fix the ecu hose which causes 65535 - Internal Control Module Memory Error and a bad ecu code.

There is a hose inside the ECU that will wear out over time and should be replaced.  I'm convinced that this problem will occur on every Mk3 VW Passat or Jetta TDI.  There are probably other TDI models overseas that use a similar system.  Yes it's unusual to have a hose inside the ECU but it's there.  This hose connects to an air sensor inside the ecu.  If an air leak occurs in this hose, the car will not run correctly.  If you are getting a check engine light (CEL or MIL) and see "65535 - Internal Control Module Memory Error" with a VCDS tool, it's most likely caused by this leaky hose.  The leak could be from the same line outside the ECU so if you have worn vacuum hoses it's a good idea to replace them all.

The OEM hose is 3mm but I went with 4mm silicone hose since my 3mm hose was stiff and the 4mm could stretch out.  There are barbs and 2 clamps that hold it in place.  4mm hose can be used for many other hoses as well.  This can be done at the same time other worn out vacuum hoses are replaced.  Silicone hose is a good choice since it stays soft when cold or hot, lasts a long time, and is more economical than the braided VW line.  The only problem with silicone is that prolonged exposure to certain oils can degrade it.  I've found that it still ages better than the OEM hose.

Since the ECU is disassembled, this is also a good time to upgrade the chip since this is an excellent basic power modification to your car.  See 1000q: basic power modifications for more details.  Note that some "FA" ECU are not socketed so open it up first to take a look before buying a chip.  It's also a good time to clean the cabin air filter if you have a Passat or add one if you have a Jetta TDI.

If one of your hoses has fallen apart then this this is a good time to replace all of your vacuum hoses.  Below is the diagram for the mk3.  This is from a 96-97 passat, your car may be slightly different.  This article refers to ECM (car computer) as ECU.  Boost pressure transducer is the n75 solenoid valve (goes to turbo wastegate can).  EGR solenoid is EGR frequency valve.  Both of these solenoids can stick so if it's convenient to remove them you can clean the insides out with carb or brake cleaner followed by a shot of wd-40.


3.5mm silicone hose (about 5 feet)  
4mm silicone hose (about 10 feet)
hoses can be purchased from

13mm wrench, screwdriver, vacuum cleaner, snips to trim the vacuum lines to fit


Cabin air filter replacement for passat (jetta TDI didn't have one stock but it can be added)

Disconnect the battery if you are also going to remove the ECU.

Remove the rubber weather stripping on the top of the engine bay firewall and plastic windshield trim (3 x plastic screws marked by yellow)

If your car is equipped with a cabin air filter, remove the bracket and filter.  This would be a good time to vacuum out any dirt or leaves.  Remove and reuse the plastic end clips on the air filter.

If you want to remove the ECU, read on, otherwise END cabin air filter replacement

ECU removal

Remove the cabin air filter and bracket.  It has (2 x 13mm) bolts and a plastic wedge holding it down

Remove vacuum hose leading into the ECU. Unbolt the near side ECU bracket (1x10mm), the other side is just a plastic clip.  

The ECU should now slide out.  You might have to tilt it or unplug the electrical connector to avoid stressing the wiring harness.  Slide the top of the plug handle out towards the vac nipple (outlined in yellow), then pull the plug handle towards you to remove the plug, as shown by the yellow arrow below.  If it's oriented like in the below picture this means you slide the outlined area (the plug handle) to the right, then pull the whole thing towards you.  

Unscrew 2 screws on 1 side of the ECU mounting bracket and just loosen the other 2.  Unscrew 4 torx screws holding the ECU in it's case and gently slide ECU out . Note: do not touch any metal part on the circuit board unless you are wearing a static electricity grounding strap.  All electronics may be damaged by very small static electricity discharges. You will now see the hose, see below for a picture, hose is outlined in yellow.

Gently unclamp the hose clamps and wiggle/twist the hose off.  One end of the hose is on a metal barb but the other is on a plastic barb on the pressure sensor.  Warning:  if the plastic barb breaks off you will need a new ECU, so be very gentle.  Try not to pull hard or at an angle.  Wiggle/twist the hose off gently!  Someone named Paramedick found that slicing the hose lengthwise at the plastic nipple end with a razor sharp blade will let you easily peel the hose off.

Cut a new length of hose matching the old length.  Installation is the reverse of removal.

ECU chip replacement and hose repair on VW TDI

Remove the ECU as shown above. 

Using a chip puller or paper clip, remove the original chip.  There are 2 spots at the corners to pry them out.  

Install the new chip.  Do NOT press directly on the chip or else it will be too far and won't have good contact resulting in your car not starting.  Press the chip in 3/4, then use a pen to roll it in the rest of the way.  Make sure it is seated flat.  Also note that some aftermarket chips are installed on a tower.  If you open the ECU and see that the chip is on a tower, you already have an aftermarket chip.  Replacing it with another brand of chip requires removal of the tower as well.

Here's a picture of a "FA" ECU from a 97 passat tdi.  Some very early FA ECU may not have removable chips so check that your ECU has removable chips before buying an aftermarket chip.  See: 1000q: mk3 jetta vs passat interchangeable parts and differences to read more about the different ECU.  The two chips that are replaced with a performance chip are labeled 357813 and 357814 with a yellow sticker.  The hose that should be replaced is on the left and outlined in yellow.

Installation is the reverse of removal.

Do you have any questions about this error code or performance chips for your Passat or Jetta TDI?  Post your comments in the forums