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Old 01-11-2025, 05:17 AM   #4
tcoradeschi
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Join Date: Oct 2022
Location: NJ
Posts: 158
Quote:
Originally Posted by mrian View Post
Thanks tcoradeschi, I appreciate the insight and I will consult the Bentleys. Did you have any rhyme or reason when looking in the door wire bundles? I'm thinking that's a reasonable spot with high wear, and thus a good place to look, but was there any other reasons you checked there?
Oh, boy. Time to put in my thinking cap, as it’s been 10+ years.

The B5.5 (this was an 02 Passat wagon, V6, 5-speed) has two CANbus circuits: a high speed circuit, which was tied to mission critical systems, ie engine controls and the like, and a low speed circuit, which was tied to all the rest. The latter included HVAC, audio, power windows, etc.

We started seeing flaky behavior in the low speed systems - radio would not turn off when exiting the car, heat controls would not work, and all of it was random in nature.

After doing some parts swapping (used HVAC controller) to no avail, I ended up with a knockoff OBD2 cable, the free version of VAG-COM, and doing repeated scans (at this point the car was our eldest child’s DD during her senior year in HS) when I could. It showed error msgs of some sort in the low speed circuit, so learning what was on that circuit was the next step.

At some point, we realized that one of the failures was the ability for the driver to raise and lower the window in driver side back door. The door switch itself would work, but not the switch on the driver’s door.

After that, it was just basic inspection of the wiring, and if wiring to a door fails, the flexible bit in the door jamb is a logical place to start. Sounds simple, but probably took a couple of months, when it was all said and done.

I have no idea what’s on the 986 CANbus, so getting smart on that would likely be your first order of business.

Hope this helps some.
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Tom Coradeschi
03 Boxster
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