Dodgy Demister

[Dellmassive]

you tried pressing and holding the button? did you do a hard reset?

can you switch on the HRS via VCDS @mmi? as a bi-directional control test?

so are we saying its a coding problem some how?

Supply fuse ok,
switch seems to be working,
BCM sees switch,
BCM sees HRS when disconnected and raises fault,
5v loop power at HRS,
good ground at HRS,

so it should be working . . . . . unless the programming is not enabling it to function?

 

[andys]

Yes, I left the battery disconnected for 30 mins, no change. Pressing and holding has the same effect as quick press, illuminates for a second and goes off.

Output test for switch illumination - nothing happens, no light at all

Output test for HRW - doesn't heat up and says "Inactive" as below

 

[mmi]

you tried pressing and holding the button? did you do a hard reset?

can you switch on the HRS via VCDS @mmi? as a bi-directional control test?

so are we saying its a coding problem some how?

Supply fuse ok,
switch seems to be working,
BCM sees switch,
BCM sees HRS when disconnected and raises fault,
5v loop power at HRS,
good ground at HRS,

so it should be working . . . . . unless the programming is not enabling it to function?

While @andys was out compared codings of 08:HVAC and 09:Centr.elec with mine. A difference was "the connection" with mirror heaters and rear heater. But that shouldn't be an issue...

Confusing part is the mysterious, steady 5.7 Volts. If that voltage would really exist across heating element that would mean 10 Amp draw... trying to think how loose/broken cable on either on +feed or ground side would cause that... because it looks like the van tries to fire up heating but detects something... not enough current draw?

1. Have you measured resistance from ground to right connector (or silvery strip in the element next to) - should be less than 0.1 ohm.
2. From ground to left connector (or silvery strip in the element next to) - should be about 0.5 ohm.
   
3. From right to left connector (heating element) should be the same about 0.5 ohms.

The above would just verify that the heating element is ok. And basically grounding...but...

Bypassing factory ground wire in the loom could be done by a separate parallel wire from right connector to proper ground... to see if it works then...​

And tailgate closed - I'm not sure if that would make any difference...

can you switch on the HRS via VCDS @mmi? as a bi-directional control test?

Interesting, don't know - never looked into tests in this area - yet

 

[Dellmassive]

im running out of ideas here,

cant believe the BCM is faulty, im still thinking a glitch in the coding for it.

might be worth dropping into the dealers and asking them to have a quick look at it and see what they say.

it might just need the BCM adaptions reset back to factory default.

 

[Dellmassive]

@mmi Confusing part is the mysterious, steady 5.7 Volts.

that voltage was with the HRS - DISCONNECTED - so no current flow/voltdrop,

its the 5v reference voltage that the BCM is putting out on the output wire to check for short to ground or short to power etc (using the internal pull up resistor inside the BCM)

Unless there IS a fault with the BCM?

might be worth checking yours @mmi to see if you get the same 5v reference voltage at the HRS when the wires are disconnected (cable disconnected means no current flow, so no volt drop, so the 5v should be present on the +12v switched live).

(we know his BCM is detecting if the HRS is disconnected as it reports back a LIVE fault that clears when the heater is reconnected)


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

this is what im thinking . . . . the 5v is the BCM detecting the curcuit

5v refence signal, not VW but they all work similar.

ie if the BCM sees - 0v/5v/12v/3.7 on the HRS cable (very low current) (before it powers the circuit with the full 22A fused supply)(self monitoring circuit)

0v - short to ground
12v short to battery +ve
5v - open circuit
3.7 - normal circuit



The BCM will retest this every key cycle/ button press/ every few seconds or whatever. - looking for faults to raise a fault code.

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

 

[andys]

im running out of ideas here,

cant believe the BCM is faulty, im still thinking a glitch in the coding for it.

might be worth dropping into the dealers and asking them to have a quick look at it and see what they say.

it might just need the BCM adaptions reset back to factory default.

Droppping into the dealers would unfortunately take a bit of organising, it's not local and it's not very often I know when I can take a day off far enough in advance to book in. I'll try the things @mmi suggested tomorrow night but other than that I don't know what else to do. The only relevant bits in the BCM programming that I can find are the ones in Byte 15 of 09 Cent Elec and they are correctly ticked.

 

[Dellmassive]

have you got the same as above?

try ticking or unticking these:

bit2 - rear window via CAN (try this both ways. set on and set off. im assuming it should OFF?)
bit3 - HRS + Mirror heating
bit6 - heated mirrors inst
bit7 - HRS inst.

im assuming the ONLY one that should be ticked is the Bit7 HRS installed (all the rest un-ticked) (and maybe bit5/bit6 if you have them fitted)

maybe try switching them all off, then just add the HRS bit and retest. (remember to do a full key cycle before a retest)

 

[andys]

have you got the same as above?

try ticking or unticking these:

bit2 - rear window via CAN
bit3 - HRS + Mirror heating
bit6 - heated mirrors inst
bit7 - HRS inst.

im assuming the ONLY one that should be ticked is the Bit7 HRS installed (all the rest un-ticked) (and maybe bit5/bit6 if you have them fitted)

maybe try switching them all off, then just add the HRS bit and retest. (remember to do a full key cycle before a retest)

Yes did all that earlier on near the beginning of the thread Like you say, options are running out. As you listed earlier in your problem solving analysis, everything seems to tally and yet it doesn't work

 

[mmi]

Bypassing factory ground wire in the loom could be done by a separate parallel wire from right connector to proper ground... to see if it works then...

The reasoning behind this came from voltage loss measurements when earlier I checked where the +feed is.

1. Noticed that from ground to right connector there was 1.0 V loss (even supposedly just a short run, thin wire perhaps).
2. The heating element "loss" was 12.2 V thus voltage at left connector was 13.2 V.
3. The loss from left connector to the battery was 1.6 V thus voltage at the battery was 14.8 V (full van's length of wire).

The only relevant bits in the BCM programming that I can find are the ones in Byte 15 of 09 Cent Elec and they are correctly ticked.

Agreed.
@andys is "DD" = "1101 1101"
Mine is "F4" = "1111 0100"

might be worth checking yours @mmi to see if you get the same 5v reference voltage at the HRS when the wires are disconnected (cable disconnected means no current flow, so no volt drop, so the 5v should be present on the +12v switched live).

(we know his BCM is detecting if the HRS is disconnected as it reports back a LIVE fault that clears when the heater is reconnected)

I'll try to check that tomorrow - it's now too cold, again down to -15C .

Anyway, thanks all - has been interesting. But have to regret that the mystery still is unresolved...

 

[andys]

The reasoning behind this came from voltage loss measurements when earlier I checked where the +feed is.

1. Noticed that from ground to right connector there was 1.0 V loss (even supposedly just a short run, thin wire perhaps).
2. The heating element "loss" was 12.2 V thus voltage at left connector was 13.2 V.
3. The loss from left connector to the battery was 1.6 V thus voltage at the battery was 14.8 V (full van's length of wire).

Agreed.
@andys is "DD" = "1101 1101"
Mine is "F4" = "1111 0100"


I'll try to check that tomorrow - it's now too cold, again down to -15C .

Anyway, thanks all - has been interesting. But have to regret that the mystery still is unresolved...

Thanks both of you for all the help

 

[Dellmassive]

hmm....

set yours to the same as MMi and see what happens?

Byte 15 of 09 Cent Elec

@andys is "DD" = "1101 1101"
Mine is "F4" = "1111 0100"

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

this wont realy help as i have no rear windows, but heres mine for reference

Address 09: Cent. Elect. (J519) Labels:. 7E0-937-BCM-V1.clb
Part No SW: 7E0 937 090 C HW: 7E0 937 090 C
Component: BCM PQ25 Max4 H82 0752
Revision: B9082001 Serial number: 4000 322170891
Coding: A0A4303A0A61343193284F507EEB9F74C294728F60CD7960330400220860

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

 

[andys]

hmm....

set yours to the same as MMi and see what happens?

Byte 15 of 09 Cent Elec

@andys is "DD" = "1101 1101"
Mine is "F4" = "1111 0100"

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

this wont realy help as i have no rear windows, but heres mine for reference

Address 09: Cent. Elect. (J519) Labels:. 7E0-937-BCM-V1.clb
Part No SW: 7E0 937 090 C HW: 7E0 937 090 C
Component: BCM PQ25 Max4 H82 0752
Revision: B9082001 Serial number: 4000 322170891
Coding: A0A4303A0A61343193284F507EEB9F74C294728F60CD7960330400220860

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

Actually that is odd, that would suggest I have the "Push to talk" function in bit 0 selected, but I don't Maybe I can't rely on the tick boxes and need to enter the actual binary or hex values directly. Another thing to try tomorrow night.

 

[Dellmassive]

just for giggles here is mine:

i have heated front screen and heated side mirrors, but NO REAR windows or HRS.

BUT bit2 is SET on mine !

so mine is "74" = "0111 0100"

 

[Pauly]

If you have changed any coding at all in your modules I would revert everything back to your base scan/default values as a test to prove any coding issues, remember many bytes are undocumented in VCDS but can still have a function
Personally I would copy paste the code into the first coding window and not bother with the long coding helper

 

[Dellmassive]

Actually that is odd, that would suggest I have the "Push to talk" function in bit 0 selected, but I don't Maybe I can't rely on the tick boxes and need to enter the actual binary or hex values directly. Another thing to try tomorrow night.

No, that value is just the "Binary equivalent" of the "HEX value" - not the first thing on the list

so

"HEX value" = "Binary value"
"DD" = "1101 1101"
"F4" = "1111 0100
"74" = "0111 0100"

try putting your HEX values in here and you will get the Binary 8bit value.

HEX to DECIMAL

.

 

[andys]

No, that value is just the "Binary equivalent" of the "HEX value" - not the first thing on the list

so

"HEX value" = "Binary value"
"DD" = "1101 1101"
"F4" = "1111 0100
"74" = "0111 0100"

try putting your HEX values in here and you will get the Binary 8bit value.

HEX to DECIMAL

.

Now that I don't get, I understand binary and hexadecimal fine, surely the 8 bits of binary code represent the bits listed in the VCDS helper from right to left, eg in the value 11011101 as mine is above then bit 0, the far right digit, has been selected as on. This is then represented by a hex value in the long coding.

 

[andys]

If you have changed any coding at all in your modules I would revert everything back to your base scan/default values as a test to prove any coding issues, remember many bytes are undocumented in VCDS but can still have a function
Personally I would copy paste the code into the first coding window and not bother with the long coding helper

No undocumented bits have been altered and the coding was reverted to known good (removing my door locking mods and drls off with handbrake), but the HRW still didn't work so I reinstated my present coding. All relevant bits in Byte 15 have been changed individually and collectively today with key cycling inbetween but has made no difference to the working of the HRW

 

[mmi]

Haven't paid attention before but sounds like there is a relay in the wiring. I had a play this morning on my way to work. I can hear very clear "click" when I push the heater button. A quieter one when the heater is powered on. And even more audible click when powered off. Sounds to be under dash - mine being LHD - I would say around A pillar (by my left knee). Can be heard even when traveling at 50km/h - and definitely at stand still engine running.

@Dellmassive A proposal re wiring diagrams - I think the Forum packs somewhat "wide/high" pictures which seems to make them a kind of blurry. Perhaps "printing" them as pdf and then attaching as files would help. Anyways, thanks all for all your diagram etc. postings - very informative and helpful .

 

[andys]

Haven't paid attention before but sounds like there is a relay in the wiring. I had a play this morning on my way to work. I can hear very clear "click" when I push the heater button. A quieter one when the heater is powered on. And even more audible click when powered off. Sounds to be under dash - mine being LHD - I would say around A pillar (by my left knee). Can be heard even when traveling at 50km/h - and definitely at stand still engine running.

@Dellmassive A proposal re wiring diagrams - I think the Forum packs somewhat "wide/high" pictures which seems to make them a kind of blurry. Perhaps "printing" them as pdf and then attaching as files would help. Anyways, thanks all for all your diagram etc. postings - very informative and helpful .

That’s interesting, thanks, another thing to check tonight. I would assume they’d keep the relay over on the left side rather than swapping it over for a RHD.

 

[Pauly]

I believe the relay is inside the BCM so always located under steering wheel