Light Switch Fault

Edit: It turned out the problem with this car was a faulty ignition switch. Most of the thread is just speculation about what the problem might be, so may or may not be accurate for other cars with similar symptoms. (In other words, the stuff about the controller coding might not be correct. It's just speculation.)

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This 2015 Mk7 Golf TDI had a new headlight installed, and now it has this fault code. The status display in the car shows "Vehicle Lighting Fault" with the headlights highlighted in orange.

The original driver's side headlight was damaged in a very minor accident a month ago. It just had a crack in the plastic, but still worked. The car was driven for a month with the headlight like this. There were no fault codes with the cracked headlight.

Today the headlight was replaced, and everything works (high-beam, low-beam, signals, marker lights, etc) AND the headlight switch in the car works properly too. I REFUSE to believe that the switch actually became defective coincidentally on this day.

Is there any way replacing a headlight could cause a switch fault code?

I've cleared the code several times and it immediately returns.

The lights are just regular halogens. Not HID lights. There's nothing fancy about them. Please tell me they don't have a supercomputer hidden in the headlight module or something.

Address 09: Cent. Elect. Labels: 5Q0-937-08X-HV1.clb
Control Module Part Number: 5Q0 937 087 N HW: 5Q0 937 087 N
Component and/or Version: BCM PQ37BOSCH 028 0106
Software Coding: 00101946404182E949E44000091407001000000000000000000000000000
Work Shop Code: WSC 00066 790 00208
ASAM Dataset: EV_BodyContrModul1UDSBosc 013004 (VW37)
ROD: EV_BCMBOSCH_013.rod
VCID: C689483779EE4B7670-8092

1 Fault Found:
919560 - Light Switch
B126A 29 [136] - Signal Implausible
MIL ON - Intermittent - Confirmed - Tested Since Memory Clear
Freeze Frame:
Fault Status: 00000001
Fault Priority: 3
Fault Frequency: 1
Reset counter: 183
Mileage: 48614 km
Date: 2017.11.15
Time: 18:27:44

A little more info.

The headlight switch will not turn on the fog lights in the bumper when the switch is pulled out. The green light on the switch illuminates, but the lights don't.

The fog lights DO turn on when the car is put in reverse (for whatever crazy reason), so they do work, as in, the wires are connected and the bulbs aren't burnt out.

The bodyshop that did the work refinished the bumper so they would have taken the bumper off and put it back on, but what on earth could that have to do with the headlight switch suddenly having a problem?

Now the status display is also saying “Starting System Fault! Service Vehicle.”

That might not be the exact words, but pretty close.

The engine starts just fine.

The buyback is still an option for this car...

Take it back to the body shop and let them sort it out.

How in the world the fogs turn on when placed in reverse without some heavy VCDS coding is beyond me.

Does the switch need to be on and the car in reverse or the fogs to come on? or, is it every time its in reverse the fogs come on?

The fog lights have always come on when the car is in reverse. I believe it's an option you can enable or disable with the touch-screen in the car. They're supposed to help you see around the car while parking or something. The thing is, this shows that the bulbs work.

The fog lights do not work when you want to turn them on with the switch. We've never used them, so they may have been like that for a long time.

Is it possible that the central electronics module that controls all this stuff would have lost its coding if the battery was disconnected while the work was done on the car?

I've looked around and there are no burnt out bulbs at all. I removed the headlights switch and put it back, just in case the wiring was loose or something. Everything looks fine.

I find it very hard to believe anything is actually broken. I very much suspect this is a problem with the coding of the central electronics module. For example, maybe it doesn't think the car has fog lights, and therefore it thinks it has the wrong headlight switch, which sets a fault code for the switch, and the fog light setting on the switch is ignored (it's the "implausible signal" that the computer reports).

We are going to return it to the body shop, to give them the first chance to have a look in case they forgot to connect something, which I doubt. The lights are all connected and working.

Once the body shop denies that they missed anything, I feel that gives us solid grounds to take it to the VW dealer for a warranty claim. If the body shop made a mistake, that's not VW's fault. If they body shop hooked everything up correctly, and the computer has decided to crap itself, that's a valid warranty claim. You should be able to change a headlight without the computer having a fit.

I don't like things I can't fix myself. If I knew what to look for in the central electronics module with VCDS, I might be able to fix it, but I haven't gone down that path yet.

So apparently auto headlights don't work anymore. When the switch is in auto, the lights come on, but they do not turn off in daylight.

It's starting to look like a module coding issue. But why? Why would the stupid module lose it's coding? If the battery was disconnected, or if the car was operated with the fog lights disconnected, could that make the computer go nuts?

Dead battery shouldn't have anything to do with it, but I could be wrong.

My only guess is the body shop may have had to swap out the module, and its got junk coding, but I can't think why they'd do that.

As for VW warranty claim, soon as they know it's been to a body shop they are going to stonewall you and point you to them.

I'm sure people here would be able to provide you example coding that would get you up in running with VCDS if you're hung out to dry.

Looking at the paperwork from the body shop all they did is remove the bumper, refinished it, replace it, and replace the headlight. No reason they would have touched anything else, and the paperwork doesn't indicate anything.

The accident was a scuff on the bumper, and a cracked headlight lens. There was no underlying damage. Everything worked properly, including the headlight, for a month after the accident. We never use the fog lights, so I'm unsure about them. They did work in the past when the car was new.

I'm strongly leaning towards the Central Electronics Control Module being coded wrong, for whatever reason.

If someone with a 2015 Golf Comfortline (or "SE" in the USA) wouldn't mind scanning their CECM (module 9, I think) and posting their sftware coding here, that would be awesome. It would have to be a car with halogen headlights, and fog lights.

Currently, the software coding for the CECM on this car is:
Software Coding: 00101946404182E949E4400009140700100000000000000000 0000000000

So, the car is back with the body shop.

Once they found out all the weird issues with the lights they said “Oh, so it’s like an Audi. We have a guy that does the programming and he’s in tomorrow.”

Okay, so WHY? Does the control module lose its coding if the battery is disconnected? If this is the expected behavior, then it would be no big deal to make a note of the coding and put it back in when the work is done. That doesn’t seem right though.

Is the CECM supposed to retain its memory? Does it have a battery or non-volatile RAM? Maybe if it has an internal battery then that battery is no good.

Edit: The car was dropped off on a Thursday, and they began working on it on Friday, then there was a long weekend, and it was finished on Wednesday. Potentially the battery may have been disconnected for five days. Maybe if a capacitor is used to retain the memory, it doesn’t last that long. So disconnecting the battery for an hour or a day might be fine, but perhaps a few days is too much and the module loses its coding and returns to a default configuration just so the car can be used, but might not have all functions working correctly.

Can anyone confirm or deny this hypothesis?

Mike_04GolfTDI said:

If someone with a 2015 Golf Comfortline (or "SE" in the USA) wouldn't mind scanning their CECM (module 9, I think) and posting their sftware coding here, that would be awesome. It would have to be a car with halogen headlights, and fog lights.
Currently, the software coding for the CECM on this car is:
Software Coding: 00101946404182E949E4400009140700100000000000000000 0000000000

Click to expand...

Here is coding info from my 2015 Golf TDI comfortline.Mine is DSG with heated seats,cruise control and multifunction steering wheel,Halogen headlights and Front Fog lights(also function as corner lights while turning steering wheel).

Thanks amitsekhon! If the body shop is unable to figure out the programming, I can probably use this to code the module.

Well, the body shop got their guy to reprogram the control module, everything worked.

Then they shut the car off, and the module had lost its memory a couple hours later. It reverts to a default setting that expects no advanced features like auto headlights and fog lights. That’s why it gives error codes. The equipment it sees is not what it expects. For example, the switch has more positions than just on and off.

Now it’s going to VW as a warranty issue. Looks like the module is simply defective. It happens.

I’d say have the accident insurance pick up the tab, worth a shot and prob less painful than dealing wit VWoA

VW dealer has had the car all day. Now they’re saying it’s doing strange things.

It better get un-strange in a hurry because the dieselgate buyback is still an option.

Changing a headlight should not cause the entire car to go haywire and become unrepairable. My only conclusion is Mk7s are ticking time-bombs of electrical gremlins.

So what’s good? Toyota? Honda? Just need a car that works around $30,000.

Stay tuned.

So get this, it turned out to be the ignition switch, replaced under warranty.

The car started doing all kinds of crazy things while the dealer had it, like you couldn’t shut the engine off if the headlights were turned on.

This does not inspire confidence in the electrical system of this car, but hopefully it was a one time freak occurrence.

Maybe one day this thread can help someone. If the car starts having all kinds of random inexplicable faults, and nothing else seems to help, maybe the ignition switch is bad.

The fact that it decided to fail just when the car was at a body shop for a headlight replacement only complicated matters. Made it look like the body shop did something, but in the end, VW covered it because the two events just don’t seem connected in any way.

That is nuts. Glad you got it sorted out. One of my cars, maybe the '02, did some crazy stuff years ago when I plugged in a new headlight one of the three blades got bent over backward. I don't recall exactly what it did but it was pretty strange. I think the blower fan would come on when you switched on the lights......