2015 GSW Leaky Sunroof causing electrical issue

First post in a long time. I searched but was unsuccessful in finding anything related to my specific issue.

Here goes:

Last Wednesday we had torrential rains. Wife reported that her GSW started leaking water onto her feet in the drivers side footwell, and that water was coming through the forward interior light fixture.

Next day she gets an MIL/CEL. I scan and it's P148b. Go online and find this 'technical tip from VW': 26-18-04TT
https://static.nhtsa.gov/odi/tsbs/2019/MC-10163514-0001.pdf

It says that water running down the drivers side A-Pillar from the leaking sunroof drain has caused corrosion on the "TUIL" Connector. That corrosion is causing a short and thus the MIL. And that you have to clean or 'repin' the connector as well as reset the Selective Catalytic Reduction system. I don't have the VAGCOM software so that's another issue.

Problem: The car 'thinks' it's out of DEF and it threatening me with not starting within 600 miles. However the DEF tank is topped off and the car runs just fine.

My question is: what's the most economical way to solve this problem? I know about the Rawtek/Malone $2k solution but that's not in my budget.

[ETA: I cleaned out the sunroof drains and the front left was clogged. I removed all 4 nipples from the ends of the hoses and will now commence cleaning regularly.]

I'm considering a software solution or disassembling the interior to get at the corroded connector. Problem is I can't find anything about a "TIUL Connector" anywhere.

I assume that it's part of the DEF system.

Why put an unsealed connector right next to a sunroof drain line that is known to leak? On an otherwise well engineered and excellent car?
At least put some heatshrink or electrical tape around it since the car can't run if it loses connection ffs.

I appreciate any insight the gurus here could provide on this issue.

My next VW (a GTI) will not have a sunroof.

First and foremost, have you had the sunroof recall service campaign rolleyes performed?

I don't know what exactly TIUL stands for, but it's basically a cluster of connectors in the driver footwell, underneath the pane right where the hood release is.

If my car had the same issues as yours, my DIY fix attempt would be to get at that, separate everything, and spray a bit of Deoxit D5 into the connectors.

Ignore the arrows and extraneous connectors (from ACC and Lane Assist retrofit) I've added in photo below - this shows you what's underneath that panel by the hood release.

Same thing happened to me last fall . Every warning light on the dash lit up . Dealer took more than a week ( and several calls to VW ) to figure it out and clean the harness connection . The service ticket says that I left the window open during a storm . Then in March I get the service campaign letter and have that done . Almost two months later I get in the car after a couple days of rain and 3/4 of the headliner is stained and wet , as is the passenger side seats and cargo area . It's been in the shop since last Thursday . Still waiting to hear from them . I really like this car , but if I had it to do again , I definitely will not get anything with sunroof again .

I have had the exact same thing happen, once I got the car up and running, took it to VW. They took that connector and several others apart, cleaned, dewatered, etc, now G2G. Everything has to be cleaned and water removed from relays etc, or you will be chasing gremlins when corrosion starts.

And they removed the flapper valves on the drain tubes, cleaned the sunroof tray.

I'm having the exact same issue as the OP (P104b,) after a heavy rain and after the dealer supposedly replaced the corroded connector. I'm trying to check what they did, but my question is how do you remove the panel covering those connectors?

You have to remove the handle for the hood release first...then it's just a matter of popping panels out/off.

There's a plastic C-clip kinda thing that holds the lever to the plastic pivot post. IIRC, you have to get a skinny screwdriver into the little gap between forward edge of release lever and the housing around it, then wedge that plastic C-clip forward to move it off.

Thanks, that and a video helped. I'll post details of the removal later. Now, I did indeed find that the Green connector (which is the one they re-pinned) was wet. Now to figure out why the sunroof is still causing issues after the warranty fix on it. I'd leave it for the dealer but it's my daughter's car, and the fault came on as she was leaving home for a cross-country trip. To say I'm not happy would be an understatement, especially when I asked the dealer if the corrosion could be as a result of the sunroof problem.

Quick followup, I'll do a detailed post later. Bottom line is I've got the leak in the sunroof frame seal, $1,700 to fix (new seal and frame) which VW is covering 70%. Not happy, guess I'll be waiting for the class action suits to work their way through and try and get reimbursed. I'll also be filing with NHTSA, since the sunroof leak can lead to a no-start condition/emissions issue.

Hi fredthe and everyone, Wondering if you're able to shared a detailed post about what you did? I'm running into the same/similar issue and from what I can make out this is the 3rd time in 3 years ... ugh/grr!! Mechanics are just taking me round in circles and doing temporary fixes so that I have to come in again and give them business. Which I get, everybody needs work! Hoping I can fix it on my own, and/or do what I need to, to prevent it from happening. Thanks

P.S. any recommendations for alternatives to Deoxit5 that are available in Canada?

Deoxit D5 available in Canada at BigSouthAmericanRiver.ca, as well as Long & McQuade (musical instruments and accessories).