High level brake light dimly lit with ign off

n0brain3r

Hi motors,

I've a 2006 B6 VW Passat it's a 3c5111 with 1.9TDi BXE engine. I came home this evening and the high level brake light is dimly lit when the ignition is off and keys out. I noticed it yesterday but put it down to a reflection.

The other brake lights stay off and everything works normally when the ignition is on the high level stays dimly lit though but lights normally when the brake pedal is pressed. I'd think it was the brake light switch but shouldn't it affect all 3? I'd a MFD2 headunit installed last week so am thinking this could have something to do with it. I've a VAG comm lead so I'll dig it out and see what a code scan reveals.

In the mean time sorry to ask such a vague question but where do I start trying to troubleshoot this? Just looking for ideas before I spend the night in the driveway trying to figure it out

Thanks in advance
nb

Plug

Bust out the wiring diagrams?

n0brain3r

I thought as much I might just disconnect it now until I've more time at the weekend. I was hoping for an easy fix! I've a copy of elsawin but all the wiring diagrams are missing any one else have access to them?

n0brain3r

Ok I've disconnected it and tested with a multimeter i'm getting nearly 11v from the socket. Can anyone tell me should I have gotten a bulb failure on the dash when I disconnected the fitting?

Vagcom showed the following

1 Fault Found
00896 - Trunk Lock Unit (F256)
008 - Implausible Signal
Freeze Frame:
Fault Status: 01101000
Fault Priority: 4
Fault Frequency: 1
Reset counter: 235
Mileage: 136526 km
Time Indication: 0
Date: 2000.00.00
Time: 21:00:05

I've seen this fault as long as I've had the car and never had trouble with the lock but it might be relevant.

About 3 weeks ago I cleared this after disabling the passanger airbag to fit a child seat
1 Fault Found
01218 - Side Airbag Igniter; Passenger Side (N200)
001 - Upper Limit Exceeded - Intermittent - MIL ON

I'm going to pull the fuses 1 by 1 at the weekend and see which kills the short anyone else know of a better way?

Tropheus

You should also check the brake light bulbs. I had an odd problem on a car a few years back. With the iginition off, when I put my foot on the brake pedal, the dash lights and all the warning lights lit up.

It turned out to be one of the elements in a brake light bulb had come loose and was touching the other element (side light) which caused a short.

n0brain3r

I'll try disconnecting both brake lamps at the weekend I don't think theres any bulbs just LEDs. I'm confused though because with the ignition off the brake lights don't light so the short must becoming from a circuit that's permanently live

Balbriggan mechanic

Quick question on this. Is the 3rd brake light on that car fitted to the bootlid or rear window? Also is there a row of capless bulbs in it or led's?

n0brain3r

It's an estate so top of the tail gate. From what I can see their leds. The voltage has dropped to nothing I think the 11v must of been a mistake the highest I got after that was about 4~5v and has resolved itself now without me doing anything. It happend after the car was parked on a slope nose down during a day of heavy rain so I'm thinking water got into something.

Owen

Would defo be an LED, 11v wouldn't be enough to saturate the junction in the LED to excite it and make it glow enough - hence the dim glow. As it's a relatively new car, it having a CAN Bus, anything could make it go mental. First instinct would be to go with the recent diagnostic result - and check the boot lock mechanism. There should be a few wires going into it, some for actuating the locking mechanism, some for the switch which registers the boot as open or closed. A short due to water in either could cause it, take em out, disassemble them and WD40 them to death, or immerse them in a bowl of dry rice to suck the water out.

Balbriggan mechanic

I agree with paint doctor. I would also check the wiring loom where it passes between the bootlid and the body for breaks or damage and where the loom joins the main loom inside the car for dampness. Older VWs use splices for joining looms and although i'm not sure whether this is the case with the 3C model passat, these splices are very succeptable to moisture damage.

n0brain3r

Thanks guys it'll be the weekend before I get to try anything I'll post when I do