Removing the ECU, and chipping, replacing the ECU hose, or
replacing the cabin the air filter.
Back
to the "how to" index page
Difficulty: 1/5
Introduction
There is a hose inside the ECU that will wear out over time and should be replaced. Yes it is 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 VAG-COM, it is most likely caused by this leaky hose. The hose is 5mm diameter, I suggest 4mm silicone hose since it can stretch out and 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 and hot, lasts a long time, and is more economical than the braided VW line.
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 on this. Note that some FA ecus 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.
Parts
3mm silicone hose (about 5 feet)
4mm silicone hose (about 10 feet)
hoses can be purchased from http://www.mcmaster.com/
13mm wrench, screwdriver, vacuum cleaner, snips to trim the vacuum lines to fit
Procedure
Cabin air filter replacement for passat (jetta TDI didn't have one stock)
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 may want to unplug the electrical connector to avoid stressing the wiring harness. Slide the top of the plug handle out, then pull up to remove the ecu plug, as seen by the yellow arrow below.
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. Warning: if the plastic breaks, 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! Cut a new length of hose matching the old length, installation is the reverse of removal.
ECU chip replacement
Remove the ecu as stated in the above directions. Make sure to check if your ECU has removable chips before buying an aftermarket chip.Using a chip puller or paper clip, remove the original chip. There are 2 spots at the corners to remove them.
Install the new chip. Do NOT press directly on the chip or else it will be too far, it will not make good contact and your car will not start. 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 is a picture of the ecu. Note that this is a "FA" ECU from a 97 passat tdi. Some very early FA ECU may not have removable chips. See: 1000q: mk3 jetta vs passat interchangeable parts and differences to read more about the different ecus. The two chips that are to be replaced 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.
Note:
Since this is a good time to replace all of your vacuum hoses, here is the
diagram for the mk3. This is from a 96-97 passat, your car may be
slightly different. Note that this article refers to ECM (car computer) as ECU.
Boost pressure transducer is the n75 valve. EGR solenoid is EGR frequency
valve. Both of these solenoids can stick, so I suggest cleaning them
out with carb or brake cleaner followed by a shot of wd-40 as long as you are changing the hoses. This will help prevent any future
problems with the solenoid sticking.
Do you know something that should be added to this article? Post your comments in the myturbodiesel.com forums