Dodgy Demister

[andys]

I've been out of action for a while and the van has gone undriven for over 2 months and so I decided to take it for a short drive this morning. Everything seems fine (it was left on trickle charge and regularly checked by a member of the family) apart from a problem with the demister. When I press the button the light stays on for about a second and then goes straight off and the rear window element and door mirror heaters don't come on (they're programmed to come on with the rear screen). If I turn the heated mirrors on via the door switch, they do work though.

Any ideas what could be the problem? I'm thinking it can't be a fuse if the light comes on briefly. I don't remember there being a problem before so I can't think what would have caused it. I've just been out to undo the triggering of the door mirrors with VCDS but it hasn't made any difference.

 

[Dieseldonkey]

Do you get a fault code on VCDS for it? I've certainly seen a fault code on Carista diagnostics for rear screen when it was disconnected.

 

[T6 Dave]

I've had similar, mines been parked up, went out and started it a few times, turned on the blower to find it only works on full.. No problems with slower speeds before... But now they don't work.. Local dealer is set to have a look into it under warranty, I thought it might have been saving amps due to not having had regen charging, only sat idling.. But dealer says no.... We shall see if I'm right or he is, as all was ok until it's layup for this period..

 

[andys]

Do you get a fault code on VCDS for it? I've certainly seen a fault code on Carista diagnostics for rear screen when it was disconnected.

Good point, I didn’t check that. I’ll go and a new scan and see what it reveals

 

[andys]

I've had similar, mines been parked up, went out and started it a few times, turned on the blower to find it only works on full.. No problems with slower speeds before... But now they don't work.. Local dealer is set to have a look into it under warranty, I thought it might have been saving amps due to not having had regen charging, only sat idling.. But dealer says no.... We shall see if I'm right or he is, as all was ok until it's layup for this period..

Bummer, blown resistor? T6s obviously get in a strop if they’re ignored!

 

[T6 Dave]

Bummer, blown resistor? T6s obviously get in a strop if they’re ignored!

Yep, that's what he suggested, but I can't believe such a new heater motor would need one at this stage.. But I suppose that might be a sign of "progress".. I'll let you guys know, and if it is, I'll let VW know my thoughts..

 

[Dieseldonkey]

Once upon a time, (when Donkey was a foal) in the age of mend and make do, I made a blower resistor using an H4 headlight wrapped in tin foil. The 2 elements ment you could work all 4 speed settings. It did the trick until I sourced the replacement part at the breakers.

 

[andys]

Managed to get outside today and did a new scan, no faults Can't understand how it can be a wiring problem, I'm sure it was fine before I was laid up and it's been shut in a garage with no vermin

 

[andys]

Can't believe I've taken a whole year to d0 anything about this, but I have. Any ideas?

1) Pressing the heated rear screen button lights the switch up for about a second before going off. The rear screen doesn't come on and no voltage is reaching the connections.

2) The door mirrors will heat up with the door switch, whether they're programmed to come on with the rear screen or not.

3) If they're programmed to come on with the rear screen then pressing the rear screen button doesn't switch them on.

4) No fault codes showing with VCDS

I'm guessing the quick flash of illumination of the switch means the switch is sending the signal to the BCM ok, but that voltage is then not being output from the appropriate connection on the BCM but can't think what could be causing it.

 

[Dellmassive]

Try disconecting the rear heater feed plugs for the back window demister and see if you get a fault code for it.?

Have you scanned the HVAC module for fault codes.?

Have you double checked the coding for the rear window demister.?

 

[andys]

Try disconecting the rear heater feed plugs for the back window demister and see if you get a fault code for it.?

Have you scanned the HVAC module for fault codes.?

Have you double checked the coding for the rear window demister.?

HVAC module reporting no fault codes, I'm off tomorrow so I'll try disconnecting the rear heater to see if it brings one up.

Now that's an interesting point I hadn't thought of, could I actually have accidentally turned off the bit that tells the BCM that the rear window is there? That would be too good to be true. In fact I'm going to grab the laptop and go outside and check that now!

 

[andys]

Of course Windows decided that this was the time it had to do an uninterruptible update so I had to stand and wait for 10 mins
While I was waiting I tried the demist button again and now it doesn't light up at all when it's pressed...

No luck with VCDS, the HVAC module doesn't contain anything to do with the heated rear window, and all the correct bits are ticked in Byte 15 of Central Elec. Just for the hell of it I unticked them, cycled power, reticked them, cycled power again, but it made no difference Shame, I was hoping for an easy fix

 

[Skyliner33]

The way that heated door mirrors work seem to be pretty random. Mine wont work with the mirror switch but do work with the rear screen button.

 

[andys]

The way that heated door mirrors work seem to be pretty random. Mine wont work with the mirror switch but do work with the rear screen button.

It's not the door mirror heaters that are the problem, they're fine, it's the heated rear window that's not working.

 

[Dellmassive]

I'll check the wiring diagram tomoz, see if that sheds any light on the situation.

 

[Dellmassive]

wing doors or tailgate? . . . . . . . . .

********************************************************
Edit:
after looking at the below, if you have no +12v at the rear heater look at:

SC6 - Fuse 6 on fuse holder C VW T6 Fusebox - Fusebox/Fuse Chart SC - Lower Dash Fusebox Listings

********************************************************

Looks like the heated rear window is fed direct from The BCM. (so it can monitor the circuit for faults)

its BCM +12v switched with a perm 0v ground.

J519 BCM terminal T73b/63 > white wire via splice B265

to > T17c - 17-pin connector, black, behind lower section of left D-pillar trim

to > rear heater Z27 + terminal and 0v ground terminal - via Earth connection 3, in left rear end wiring harness & Earth point, on left D-pillar

ill dig out the fuse and switch info. . . . . . .




************************************

edit:

Heated rear window switch, Climatronic control unit, Air conditioning system control unit, Onboard supply control unit, Fuse 6 on fuse holder C

K10 - Heated rear window warning lamp
L39 - Heated rear window switch illumination bulb
E15 - Heated rear window switch
J519 - Onboard supply control unit

The front switch is connected direct to the BCM.


SC6 - Fuse 6 on fuse holder C VW T6 Fusebox - Fusebox/Fuse Chart SC - Lower Dash Fusebox Listings





here is another pic showing both rear door types . . . .

 

[andys]

wing doors or tailgate? . . . . . . . . .

********************************************************

after looking at the below, if you have no +12v at the rear heater look at:

SC6 - Fuse 6 on fuse holder C VW T6 Fusebox - Fusebox/Fuse Chart SC - Lower Dash Fusebox Listings

********************************************************

Looks like the heated rear window is fed direct from The BCM.

its BCM +12v switched with a perm 0v ground.

J519 BCM terminal T73b/63 > white wire via splice B265

to > T17c - 17-pin connector, black, behind lower section of left D-pillar trim

to > rear heater Z27 + terminal and 0v ground terminal - via Earth connection 3, in left rear end wiring harness & Earth point, on left D-pillar

ill dig out the fuse and switch info. . . . . . .


View attachment 38271 View attachment 38272

************************************

edit:

Heated rear window switch, Climatronic control unit, Air conditioning system control unit, Onboard supply control unit, Fuse 6 on fuse holder C

K10 - Heated rear window warning lamp
L39 - Heated rear window switch illumination bulb
E15 - Heated rear window switch
J519 - Onboard supply control unit

The front switch is connected direct to the BCM.


SC6 - Fuse 6 on fuse holder C VW T6 Fusebox - Fusebox/Fuse Chart SC - Lower Dash Fusebox Listings

View attachment 38274



here is another pic showing both rear door types . . . .

View attachment 38275

Great thanks. It’s a tailgate

 

[Dellmassive]

cool, keep us posted,

seems strange that there is no fault logged,

i would check:

the SC6 supply fuse,?
a good ground at the heated screen at the rear?
VCDS BCM coding,?
look at VCDS to ensure the BCM is seeing the press switch operation.?
try disconnecting the rear heater and try turning it on to see if a fault is logged.?
try disconnecting the battery for 30mins to do a BCM hard reset.?

maybe the light was going off straight away as it was detecting a fault?


i havent got rear windows on mine so cant do any tests here for you.

@Loz has some screen shots you could compare . . . . .

Bcu Central Electrics Module 09 Byte Screen Shots



.

 

[andys]

@Dellmassive Thanks for the diagram, I couldn't find that one when I looked in the Downloads section

The fuse in SC6 is fine, I checked the right bits were ticked in Byte 15 last night so it's not the coding.

One other piece of info though, the switch DOES still light up for a second when pressed, but only when the engine is running, with the ignition on but engine not running, it doesn't illuminate at all. Fully charged battery (on trickle charge and voltage checked)

Scan as below, no fault codes

----------------------------------------------------------------------------------------------

Tuesday,05,March,2019,10:03:33:44671

VCDS -- Windows Based VAG/VAS Emulator Running on Windows 10 x64

VCDS Version: 18.9.1.0 (x64)  HEX-V2 CB: 0.4436.4

Data version: 20190114 DS296.0

www.Ross-Tech.com



VIN:   License Plate:

Mileage: 19780km-12290mi   Repair Order:



Chassis Type: 7H-VN75 (7E0)

Scan: 01 02 03 04 08 09 10 13 15 17 19 25 5F 61 0B


VIN:   Mileage: 19780km-12290miles


01-Engine -- Status: OK 0000

02-Auto Trans -- Status: OK 0000

03-ABS Brakes -- Status: OK 0000

04-Steering Angle -- Status: OK 0000

08-Auto HVAC -- Status: OK 0000

09-Cent. Elect. -- Status: OK 0000

10-Park/Steer Assist -- Status: OK 0000

13-Auto Dist. Reg -- Status: OK 0000

15-Airbags -- Status: OK 0000

17-Instruments -- Status: OK 0000

19-CAN Gateway -- Status: OK 0000

25-Immobilizer -- Status: OK 0000

5F-Information Electr. -- Status: OK 0000

61-Battery Regul. -- Status: OK 0000

-------------------------------------------------------------------------------

Address 01: Engine (2D2D2-CXHA)       Labels:. 04L-907-309-V2.clb

   Part No SW: 04L 906 056 KG    HW: 04L 907 445

   Component: R4 2.0l TDI   H02 3771

   Revision: 23002001

   Coding: 00254014436501090000

   Shop #: WSC 02737 790 50316

   ASAM Dataset: EV_ECM20TDI03004L906056KG 004004

   ROD: EV_ECM20TDI03004L906056KG_004.rod

   VCID: 7CA2FC4616618017C25-8028


No fault code found.

Readiness: N/A


-------------------------------------------------------------------------------

Address 02: Auto Trans (J743)       Labels:. 0BH-927-711.clb

   Part No SW: 0BT 300 046 J    HW: 0BH 927 711 G

   Component: DSG DQ500-7F  H11 5301

   Revision: 00H11V01

   Coding: 0014

   Shop #: WSC 00000 000 00000

   ASAM Dataset: EV_TCMDQ500021 001001

   ROD: EV_TCMDQ500021.rod

   VCID: 3D2431424DFB491FB5B-8068


No fault code found.


-------------------------------------------------------------------------------

Address 03: ABS Brakes (J104)       Labels: 7E0-907-37x-MK100ESC.clb

   Part No SW: 7E0 907 379 Q    HW: 7E0 907 379 N

   Component: ESC           H06 0133

   Revision: 00000000    Serial number: 42226000000264

   Coding: 517E4098256684868A7C027BA48221D679F700

   Shop #: WSC 02739 790 50316

   ASAM Dataset: EV_Brake1ESCCONTIVN75XGP2 011001

   ROD: EV_Brake1ESCCONTIVN75XGP2_011.rod

   VCID: 40DA48B63A0924F7DED-8014


No fault code found.


-------------------------------------------------------------------------------

Address 04: Steering Angle (G085)       Labels:* 6R0-959-654.clb

   Part No SW: 6R0 959 654     HW: 6R0 959 654

   Component: LENKW.SENSOR  H07 0070

   Serial number: 31081613470560

   Coding: 01

   Shop #: WSC 00000 000 00000

   ASAM Dataset: EV_LWSKLOVW25X 005001

   ROD: EV_LWSKLOVW25X.rod

   VCID: 7EA6F64E007D9207EC1-802A


No fault code found.


-------------------------------------------------------------------------------

Address 08: Auto HVAC (J301)       Labels:| 7E5-907-047.clb

   Part No SW: 7E0 907 047 AC    HW: 7E0 907 047 AC

   Component: Climatic-T5   H22 0708

   Revision: 00001002

   Coding: 0000000003

   Shop #: WSC 02737 790 50316

   ASAM Dataset: EV_ClimaticT5 A01003

   ROD: EV_ClimaT5Basis.rod

   VCID: 6B80CF1A630F17AF5BF-803E


No fault code found.


-------------------------------------------------------------------------------

Address 09: Cent. Elect. (J519)       Labels:. 7E0-937-BCM-V1.clb

   Part No SW: 7E0 937 090 B    HW: 7E0 937 090

   Component: BCM PQ25 Max4 H81 0744

   Revision: B9081001    Serial number: 0982 247160737

   Coding: 2F8039B828613C92802875F47E6D9CDDFFA471FF60CC4DF0320400230840

   Shop #: WSC 02737 022 186923

   VCID: 2A0E0A1EACF5CEA7E09-807E


   Subsystem 1 - Part No SW: 7E0 959 801 Q    HW: 7E0 959 801 Q  Labels: 7E0-959-80X-V2.CLB

   Component: J386__TSG_FT  003 0653

   Serial number: KU0KU030081662434740

   Coding: 1400B1


   Subsystem 2 - Part No SW: 7E0 959 802 Q    HW: 7E0 959 802 Q  Labels: 7E0-959-80X-V2.CLB

   Component: J387__TSG_BT  003 0653

   Serial number: KU0KU030081662436077

   Coding: 0400A1


   Subsystem 3 - Part No: 1K0 951 605 C

   Component: LIN BACKUP HO  H05 1501

   Coding: 000000


   Subsystem 4 - Part No SW: 7E0 959 442 A    HW: 7E0 959 442 A  Labels: 3C8-959-537.CLB

   Component: E221__MFL-DC1  H02 0103

   Serial number: 29160001512780026341

   Coding: B4FFFF


No fault code found.


-------------------------------------------------------------------------------

Address 10: Park/Steer Assist (J446)       Labels:| 7E0-919-475.clb

   Part No SW: 7E0 919 475 AA    HW: 7N0 919 475

   Component: PARKHILFE 8K  H06 0212

   Revision: --------    Serial number: 28261619402473

   Coding: 10810C

   Shop #: WSC 02737 790 50316

   ASAM Dataset: EV_VW75XParkAssis8K 001012

   ROD: EV_VW75XParkAssis8K_001_VN75.rod

   VCID: 71BCDD724123FD7F613-8024


No fault code found.


-------------------------------------------------------------------------------

Address 13: Auto Dist. Reg (J428)       Labels:| 7N0-907-572.clb

   Part No SW: 7N0 907 572 C    HW: 7E0 907 572

   Component: ACC Bosch PQx H03 0210

   Serial number: 10081604391480

   Coding: 00005000FE0779

   Shop #: WSC 01383 790 50316

   ASAM Dataset: EV_ACCBEGVW361 001006

   ROD: EV_ACCBEGVW361_VW32.rod

   VCID: 36362E6E68CD9A47741-8062


No fault code found.


-------------------------------------------------------------------------------

Address 15: Airbags (J234)       Labels:| 5K0-959-655.clb

   Part No SW: 7E0 959 655 G    HW: 7E0 959 655 G

   Component: VW10Airbag021 H08 0018

   Revision: --------    Serial number: 003V3001ZSZ7

   Coding: 000000000000000000000000000000003231

   Shop #: WSC 02734 790 50316

   ASAM Dataset: EV_AirbaVW10BPAVW12X 001028

   ROD: EV_AirbaVW10BPAVN750_VW12.rod

   VCID: 3A2E3A5E5CD57E27909-806E


No fault code found.


-------------------------------------------------------------------------------

Address 17: Instruments (J285)       Labels:| 5K0-920-xxx-17.clb-SRI1

   Part No SW: 7E0 920 970 S    HW: 7E0 920 970 S

   Component: KOMBI         H03 1104

   Serial number: 00000000000000

   Coding: 750F010300

   Shop #: WSC 02737 790 50316

   ASAM Dataset: EV_Kombi_UDS_VDD_RM09 A05733

   ROD: EV_Kombi_UDS_VDD_RM09_005_VW25.rod

   VCID: 3A2E3A5E5CD57E27909-806E


No fault code found.


-------------------------------------------------------------------------------

Address 19: CAN Gateway (J533)       Labels:. 7E0-909-901.clb

   Part No SW: 7E0 909 901     HW: 7E0 937 090

   Component: GW-K-CAN TP20 H81 0744

   Revision: B9081001

   Coding: 042305

   Shop #: WSC 02737 022 186923

   VCID: 688AB01672793CB736D-803C


No fault code found.


-------------------------------------------------------------------------------

Address 25: Immobilizer (J334)       Labels:| 5K0-920-xxx-25.clb

   Part No SW: 5K0 953 234     HW: 5K0 953 234

   Component: IMMO          H03 1104

   Serial number:             

   Coding: 000000

   Shop #: WSC 00000 000 00000

   ASAM Dataset: EV_Immo_UDS_VDD_RM09 A03710

   ROD: EV_Immo_UDS_VDD_RM09.rod

   VCID: 6A8ECA1E6CF50EA7209-803E


No fault code found.


-------------------------------------------------------------------------------

Address 5F: Information Electr. (J794)       Labels:| 5G0-035-MIB-ENT2.clb

   Part No SW: 1K8 035 150 H    HW: 1K8 035 150 H

   Component: MU-E--ER      055 7067

   Serial number: 18081600010179

   Coding: 065700003C00000041110001000000001F0000C60000010001

   Shop #: WSC 02737 790 50316

   ASAM Dataset: EV_MUEnt4CGen2LGE 001032

   ROD: EV_MUEnt4CGen2LGE_VW12.rod

   VCID: 2A0E0A1EAC75CEA7E09-807E


No fault code found.


-------------------------------------------------------------------------------

Address 61: Battery Regul. (J840)       Labels:. 1K0-907-534.clb

   Part No SW: 7E0 907 534     HW: 7E0 937 090

   Component: Batt.regelung H81 0744

   Serial number: 0982 247160737

   Coding: 030B1A73

   Shop #: WSC 02739 790 00000

   VCID: 688AB01672793CB736D-803C


   Subsystem 1 - Part No SW: 7E0 915 181 K    HW: 7E0 915 181 K

   Component: J367-BDMConti  H03 1050

   Serial number: 75410903001608151220


No fault code found.


End----------(Elapsed Time: 01:23, VBatt start/end: 12.7V/12.4V)-----------

 

[andys]

Where are the wiring connections to the heated rear screen element? I've just realised the 2 metal contacts opposite each other on the window are both ground so the + connection to the element must be elsewhere. This is where I was measuring for voltage so I obviously wouldn't get any there. I've looked all the way through the T5 Haynes as I assumed that wouldn't have changed much, but it makes no mention anywhere of a heated rear window on the T5 at all.