2012 Passat TDI SEL Pulse Wave Modulation

oilbrnr

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Dec 18, 2001
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Connecticut
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'12 Passat TDI SEL, '10 Dodge 2500 Cummins
I am tackling some wiring with my car and have come to understand the basic concept of Pulse Wave Modulation. It could have significant bearing on the project as a whole. I am not convinced that my car uses this technology however and would like to hear from any who might say definitively whether my car is PWM or not. I don’t have acces to anything more sophisticated than a light duty volt/ohm meter to make tests. My car does not have LED headlights and I believe all my taillights are traditional filament bulbs. Clearly the CHMSL is LED but would not require PWM dimming. What say all of you?
 

Fixmy59bug

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Aug 1, 2009
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Las Vegas, NV
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2015 Passat TDI SE
Yes, your headlights and taillights are definitely absolutely PWM controlled.

If you have access to a VCDS, you can see that the bulb saver (I forget the exact term) function is active on the headlights to extend the life by regulating the voltage (via duty cycle).

The taillights are single filament bulbs. And in order to make them function at dual brightness levels (running lights and brake/turn lights), it regulates the voltage (again via duty cycle).is also regulates the brightness of the DRL in the same manner.

This duty cycle regulation is Pulse Width Modulation.

I can not say for certain if the CHMSL is PWM controlled or not.
 

oilhammer

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outside St Louis, MO
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There are just too many to list....
There are ALL kinds of PWM bits on that car. From the lighting to the braking to the steering. All modern cars have that sort of stuff at least somewhere.
 

740GLE

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2015 Passat SEL, 2017 Alltrack SE; BB 2010 Sedan Man; 2012 Passat,
A lot of the motors are controlled by PWM (pulse width modulation) as well if you aren't that old or your hearing hasn't gone, with the car running you can her a high pitched hummmm/whine its about 1-5KhZ not sure, but that's the switching frequency of the exhaust flapper valve/intake flapper as well. Between PWM and sensors or encoders the ECU can fine tune a control valve almost infinitely from 0-100%.

What are you trying to accomplish?
 

Fixmy59bug

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2015 Passat TDI SE
Based upon his other posts “Can’t find brake light signal” and “Trailer brake controller” I’d wager a guess that he is trying to find a brake light signal for a trailer brake controller.
 

oilbrnr

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Dec 18, 2001
Location
Connecticut
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'12 Passat TDI SEL, '10 Dodge 2500 Cummins
so the goal here was to use a suitable wire to "trigger" a brake controller used to operate electric brakes on a small camper/trailer. The common thought is that any duty cycle pulsing is probably too fast for the brake controller to care. That said, I would prefer to use an unadulterated solid signal if possible. My thought is that the CHMSL, even if it is PWM controlled, would be always lit to a consistent level and probably at full brightness.
Another problem I have encountered is that the brake controller has a manual override used to put brakes on the trailer only (usually in an emergency). When the override is applied the controller send a "reverse" signal through the trigger wire to illuminate brake lamps on the trailer (and car). Needless to say the VW hates this and sends all sorts of error messages warning of lights not working. The solution seems to be wiring a diode to limit signal in one direction only. This will disable any display of brake lights in manual mode but it seems the best I can do.
 

oilhammer

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outside St Louis, MO
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There are just too many to list....
Shame you can't just get a plug-n-play trailer controller for these.

I actually just looked in ETKA and they do not even show any trailer stuff for the newer real Passat either. Strange. Plenty for other models (Golf, etc.) though.

Sucks because the "info" is already floating around the CAN bus, just no easy way to tap into it and decipher the necessary inputs. The control modules are really nice. Because it does so much more than supply a brake signal. It detects the trailer is connected and changes the parameters of all kinds of things, from ABS/ESP operation to transmission shift maps, proximity sensors, rear gate operation, and on some models you can even do a quick couple steps that will force the reverse lights to stay on even after the transmission has been taken out of reverse so you can see in the dark to hook up the trailer!
 

740GLE

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NH
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2015 Passat SEL, 2017 Alltrack SE; BB 2010 Sedan Man; 2012 Passat,
Cant you just tap the brake switch by the brake pedal to a trailer brake controller then send the trigger wire back to the wiring?
 

oilhammer

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outside St Louis, MO
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There are just too many to list....
Cant you just tap the brake switch by the brake pedal to a trailer brake controller then send the trigger wire back to the wiring?
No such switch. At least, not on other VAG models starting around late 2006. They use a Hall sender on the side of the master cylinder in conjunction with a pressure sensor in the ABS unit. Hence the OP's initial query. Don't think the NMS has a switch on the pedal. I don't remember seeing any during the Chinese HVAC motor R&R on them:

 

tadawson

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2013 Passat TDI SEL, 2015 Passat TDI SEL
Perhaps complicated, but then again, hall effect sensors don't inevitably fail. I can't recall any car I have owned with a mechanical switch that didn't die at some point . . .
 

740GLE

Top Post Dawg
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NH
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2015 Passat SEL, 2017 Alltrack SE; BB 2010 Sedan Man; 2012 Passat,
No such switch. At least, not on other VAG models starting around late 2006. They use a Hall sender on the side of the master cylinder in conjunction with a pressure sensor in the ABS unit. Hence the OP's initial query. Don't think the NMS has a switch on the pedal. I don't remember seeing any during the Chinese HVAC motor R&R on them:

So how does the westfaila OEM trailer wiring work on other cars, does it read separate signals from the BCM/CAN Bus?
 

oilhammer

Certified Volkswagen Nut & Vendor
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outside St Louis, MO
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There are just too many to list....
Yes, it just has a "tap" on the CAN paired wire bus and gets any data needed. The other modules, primarily the CAN Gateway, need to be told there is a new kid on the block, so to speak, to play nice with it, but that is about it. You may have some coding changes to do, to. Just depends on the model.

Most recently I have done two on Audi Q5s, which is the model of perfection when it comes to this sort of thing. The plugs are already there, neatly taped to the rear harness in the right rear corner of the car. The mounting bracket for the trailer interface module is already there. All the holes to route the wire harness from the module down through the body are already there, just push the plugs out. Mounting holes already there in the unibody rail. Just install it all, then go in and do the Gateway initialization, which is basically the way you tell the Gateway to go out and reevaluate all the modules on the CAN bus, so it picks up the trailer controller, then on that one you have to go into the Parktronic and a couple other modules and use VCDS' wonderful long coding helper and check a couple boxes where it says "trailer module equipped" or whatever the wording is, and then bingo, it all works.

Seems silly, but one of the nicest things is when a trailer is attached, the Parktronic knows, so it defeats the 'BEE-BOO-BEE-BOO-BEE-BOO!' alarm when backing up. :p
 

jrm

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2013 Passat SE with nav (totaled)
I cant stand PWM on LED lights, mostly Toyotas as the new DRL's on those rigs flicker and distract me. im a old school computer gamer and am used to frame rates above 120, so PWM is very noticeable to me :mad: Its like looking at a bright light threw fan blades
 

Jedadiah

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Central Kentucky
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Former: '15 Passat TDI SE 6M, '15 Golf S 6M and '10 JSW
The oem trailer wiring options don’t power trailer brakes either, so finding a brake signal for the brake controller is always an issue. On my mk6, which I think has the same bcm as an nms, I was able to get the signal from the brake output on my trailer module, which isn’t normally used when coded to NAR. I just ran a wire from the module to the controller when I installed the oem trailer wiring.

On my MK7, this didn’t work. The module cuts the brake signal output on the trailer module when recoded, so I had to get the signal elsewhere. At first I used the brake signal wire from the bcm to my trailer module. It worked, but did some weird things like coming on when the car was off that made me wonder if it was working right.

I did a little reading on a Tiguan forum, and guys said they had no problem using the output from the bcm to the third brake light. It’s usually an led, so the car doesn’t check it the same way, so the brake controller doesn’t throw bulb lights. I tapped this wire on my Golf and the brake controller has worked properly ever since. I can make the car tell me to check the third brake light if I keep pulling the manual override lever with NO trailer attached, but that’s the only time it’s come on, and not something I ever really do.

My bought back JSW had the same BCM part number as my current 15 NMS, so I assume it’ll work similary. If someone with Erwin can figure out what output is from the bcm to the third brake light, I think it’ll solve the op’s problem, and be easier than tracing it from the back to the front, which some of the Tiguan guys did.
 

oilbrnr

Member
Joined
Dec 18, 2001
Location
Connecticut
TDI
'12 Passat TDI SEL, '10 Dodge 2500 Cummins
The oem trailer wiring options don’t power trailer brakes either, so finding a brake signal for the brake controller is always an issue. On my mk6, which I think has the same bcm as an nms, I was able to get the signal from the brake output on my trailer module, which isn’t normally used when coded to NAR. I just ran a wire from the module to the controller when I installed the oem trailer wiring.

On my MK7, this didn’t work. The module cuts the brake signal output on the trailer module when recoded, so I had to get the signal elsewhere. At first I used the brake signal wire from the bcm to my trailer module. It worked, but did some weird things like coming on when the car was off that made me wonder if it was working right.

I did a little reading on a Tiguan forum, and guys said they had no problem using the output from the bcm to the third brake light.
It’s usually an led, so the car doesn’t check it the same way, so the brake controller doesn’t throw bulb lights. I tapped this wire on my Golf and the brake controller has worked properly ever since. I can make the car tell me to check the third brake light if I keep pulling the manual override lever with NO trailer attached, but that’s the only time it’s come on, and not something I ever really do. .

My bought back JSW had the same BCM part number as my current 15 NMS, so I assume it’ll work similary. If someone with Erwin can figure out what output is from the bcm to the third brake light, I think it’ll solve the op’s problem, and be easier than tracing it from the back to the front, which some of the Tiguan guys did

Almost exactly my experience. FYI to all...a diode has been wired inline from 3rd brake light and everything iss working very well!!! Thanks to all
 
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