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A3 Volkswagen ECM Identification, Removal, and DisassemblyBy Uwe Ross 9. Nov.97
The ECM is located in the "gutter" under the passenger side half of the black plastic rain shield at the base of the windshield. To remove the rain shield, you'll need a Philips head screwdriver, and something the pry with.
Looking at the rainshield, you'll notice that 7 black plastic fasteners that secure it. You only need to remove 4 of these. Start with the fastener closest to the passenger side A-pillar. This one just unscrews. Set it aside.
The other three are a bit funky. Youíll find yourself getting absolutely nowhere if you simply try to unscrew them. The secret is to pry up on them while unscrewing at the same time. The screw will only come out about 1/4", and then it's all pry. The screw is captive in an expanding plastic clip; you'll see what I mean after you get the first one out.
After you get all three of these fasteners out (you might do some cursing the first time you do this), find the clip that holds the two halves of the rainshield together in the very center. Slide the clip towards the passenger side of the car, it will remain attached to the piece of the rainshield you are about to remove. Be careful here, at least one person has reported breaking the piece that the clip slides over upon re-installion by being "ham-handed".
Lastly, remove the rubber gasket that attaches the front of the rain shield to front lip of the cowl gutter by pulling straight up on it starting at the passenger side end.
Now pull the passenger side half of the rainshield out; this takes a little wiggling, pull mostly towards the front of the car.
Your ECM is now visible. If youíre getting ready to order a chip, you need to write down the ECM part number; itís on a label that should be easily visible. The part number on mine is 021 906 259 AA.
Reinstalling the rain shield is the reverse of removal. When reinstalling the three funky fasteners, note that the plugs are rectangular, as are the holes they go into. Orient them properly in the holes. You may need to squeeze the "wings" together a little to get them started, then push down on the "screws" using your Philips head screwdriver. No twisting action is necessary.
It may be prudent to disconnect the battery (at its negative post) before proceeding. I've pulled my ECU at least three times without doing so, but if you leave the battery connected and smoke something, don't say I didn't warn you.
In order to remove the ECU from the car, first disconnect the wiring harness. The end of harnessí connector closest to the back of the car has a sliding latch. Slide the latch towards the back of the car and the connector will almost unplug itself.
Remove the bolt on the driver's side of the ECM mounting bracket using a 10mm wrench.
Loosen the nut at the passenger's side of the bracket using a 10mm wrench; it is not necessary to remove this nut.
Slide the ECM slightly towards the passenger side so that the slot in the bracket comes out from under the nut and the remaining plastic fastener towards the rear of the bracket come loose.
The ECM can now be removed from the car. I find it easiest to slide it along inside the gutter towards the HVAC intake where thereís a little more room to pull it out.
In theory, this is best done in a "static controlled" environment, especially in the winter or in a low humidity situation. If in doubt, ground yourself and the metal end of the ECM to a water pipe using a couple of pieces of wire. I don't normally do this, but again, don't say I didn't tell you.
The ECM has two ends, the end that the harness connector was plugged into is made of aluminum, while the other end is plain plastic with a filtered "breather" protruding from it..
Remove the two Philips-head screws that hold the mounting bracket to the aluminum end.
Remove the four T10 or T15 screws that hold the aluminum end to the plastic case using an appropriate Torx driver or wrench.
You can now gently remove the plastic housing from the aluminum end. It may be necessary to pry a little with a knife blade where the aluminum meets the plastic housing. The circuit board will stay attached to the aluminum end.
Refer to your chip vendorís instructions here. Some ECMs have a DIP-style chip in a socket, some have a PLCC-style chip. The PLCC type is easiest to remove with a special tool designed just for that purpose, it is available from Radio Shack, p/n 276-2101 for under $10.
In any case, pay particularly close attention to the orientation of the chip. DIP chips have a small U-shaped notch on one end: PLCC chips have a bevel along one edge. Putting your new chip in wrong can ruin it.
This is simply a matter of sliding the board back into the case and reinstalling the four Torx screws and the two Philips screws. However, it is possible to put the board in upside down. Put the board in so that the chip socket faces the top of the housing that has the identifying part-number label on it.
Re-secure the ECM to its mounts using a 10mm wrench.
Slide the latch on the harness connector all the way to itís "unlatched" position. Bring the harness connector into contact with the mating connector on the ECM, then slide the connector latch towards the front of the car to secure it.
At this point, I always start the car up (just to make sure) before reinstalling the rain shield. If the car starts, you know the chip is in properly and working, and the harness connector is connected.
Reinstall the rainshield.
If your car is more than a year old, it couldnít hurt to remove both halves of the rainshield and clean out any debris thatís accumulated under it. Pay special attention to the drain on each end. If these drains are allowed to become clogged with debris, your HVAC system could become flooded with water and on some older VWs, the ECM could also get soaked, although the A3 cars seem to be less prone to that. If you park your car outside a lot and if it spends any time under trees in the fall, it's a good idea to pull the rainshield for a cleaning at least once a year.
Previous VWs had problems with corrosion of the harness connectors; this would lead to all kinds of flaky symptoms. Itís not a bad idea to treat the connector pins at the ECM to some anti-corrosive spray. Do not use WD-40 or Silicon Spray. WD-40 will actually attract moisture after itís been in place for a while and worsen corrosion. Avoid using Silicon Spray under the hood at all times, if the engine inhales the spray, it can ruin your Oxygen Sensor(s). I like ACF-50; a product made for the aircraft industry.
I developed these instructions using my 1997 GTI-VR6. They are probably applicable to all A3 VWs, i.e. 1993-1998 Golf, GTI, and Jetta. However, I cannot be held responsible for any errors or omissions. If you have any suggestions how to improve these instructions, send me some e-mail.
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