Rear Fog Light Issues

[marcrmercado]

I've done my homework and I'm almost to the point where I'm gonna have to sorrowfully handover a huge chunk of my hard earned money to a dealership to fix it.

I have a 2007 Audi A4 S-Line 2.0T 6 M/T B7.

I bought the car with both rear fogs not working. It's to a point where it's bugging me the heck now. I've looked at videos, previous posts and put in my time for a decent amount of research. Still no luck.

1.) My ground wire is good for both and I've tested it with another live brake line.

2.) I've tried to see if the 8E0 907 279N module was to blame by replacing and it's still the same problem.

3.) It's hard to test the 23 and the 32 pin connectors and place a voltmeter in there, because of the lack of room.

4.) The right fog used to work, but now it's dead. Before then, it would turn on when the trunk was halfway up then turn off if moved away from its sweet spot.

5.) I wasn't getting any voltage from the left fog, and again, both ground for left and right are good.

***It's almost like this to me: 😐🔫

*****if any folks are here in Northern Utah, I can pay for some service calls for this.

[Biged243]

Rear fog? Anyways sounds like worn/broken wires if one worked when the trunk was at a certain point. Trace the wires and look in that area.

[waiapasi2006]

That's a hard one to pinpoint OP. It could be from a basic fix to a terrifying one. Did you try wiggling the wires while your trunk were at that position to see what happens?
How about your fuse and light switch?

[marcrmercado]

Is there a fuse for that? I have printed about a 22 page wiring diagram and I've also looked into any possible fuses it could be linked into that's on the driver's side. I saw some front fogs but no rear. Are they linked together?

I'll tackle it again in a day or two once I'm a little more settled down. It's hard when you work 6 days a week, but I'll look at it again. Updates to come.

[B7Joe]

If moving the trunk up/down affected the lights then sounds like a potential wiring/harness issue to me. Could also be the sockets. Are they oxidized or are any contacts loose?

[marcrmercado]

The sockets (the unit that connects the bulb holder and the wiring) looked clean. When it worked, I took the bulb holder from the left and tried on the right and it worked.

It was intermittent. Sometimes, it'll work with the trunk halfway up and sometimes it'll work when it's closed and turn off when the trunk is lifted.

I'm half expecting that I would have to take out the trunk interior to get to the wiring. Any possible pointers how to do the testing from the source first?

[BenMTL]

Sounds like a loose contact problem, not ground.

Have fun following the line Do you ever use rear fog though? I know I haven't in the past 2-3 years as they almost do nothing for me so I'd personally just ignore it if I had that problem.

[marcrmercado]

I don't use it, but the fact that it gives me an annoying warning beep every time is what drives me to put some attention in it. How would you disconnect so the diagnostic system won't see it?

[Biged243]

http://en.wikipedia.org/wiki/Automot...Rear_fog_lamps

In Europe and other countries adhering to ECE Regulation 48, vehicles must be equipped with one or two bright red "rear fog lamps" (or "fog taillamps"), which serve as high-intensity rear position lamps to be energised by the driver in conditions of poor visibility to enhance vehicle conspicuity from the rear. The allowable range of intensity for a rear fog lamp is 150 to 300 candelas,[15] which is within the range of a U.S. stop lamp.[5] For this reason, some European vehicles imported to the United States have their rear fog lamps wired as stop lamps, since their European-specification stop lamps may not be sufficiently intense to comply with U.S. regulations, and in North America rear fog lamps are not required equipment. However, they are permitted, and are found almost exclusively on European-brand vehicles in North America — Audi, Jaguar, Mercedes, MINI, Land Rover, Porsche, Saab and Volvo provide functional rear fog lights on their North American models. The final generation Oldsmobile Aurora also had dual rear fog lights installed in the rear bumper as standard equipment.

Most jurisdictions permit rear fog lamps to be installed either singly or in pairs. If a single rear fog is fitted, most jurisdictions require it to be located at or to the driver's side of the vehicle's centreline — whichever side is the prevailing driver's side in the country in which the vehicle is registered.[15] This is to maximise the sight line of following drivers to the rear fog lamp. In many cases, a single reversing lamp is mounted on the passenger side of the vehicle, positionally symmetrical with the rear fog. If two rear fog lamps are fitted, they must be symmetrical with respect to the vehicle's centreline.[15] Proponents of twin rear fog lamps say two lamps provide vehicle distance information not available from a single lamp. Proponents of the single rear fog lamp say dual rear fog lamps closely mimic the appearance of illuminated stop lamps (which are mandatorily installed in pairs), reducing the conspicuity of the stop lamps' message when the rear fogs are activated. To provide some safeguard against rear fog lamps being confused with stop lamps, ECE R48 requires a separation of at least 10 cm between the closest illuminated edges of any stop lamp and any rear fog lamp.[15]

Well, I learned something new. This is for people that might not know exactly what your talking about rear fog lights.

[marcrmercado]

Haha I didn't know they existed until I owned an Audi. It would be nice to not have the rear fog lights out since they act as brake lights as well. I know that you pull the knob two clicks out to activate the rear fog, but mine most likely has a short. As I said, updates in about 2 days.

[marcrmercado]

Okay, so I took apart my trunk and found that my rear fog wiring definitely did have a short as suggested by some of you. I've spliced the wiring and made my own.

Here is the kicker. Both are now running at about 9 and 10 volts. The higher side powers on and when I try the lower voltage bulb to the higher voltage bulb, it lights up.

What gives? I feel like I'm so close!!!

[marcrmercado]

By that, I mean one side (higher voltage) lights up and the other does not when they're only a volt difference.

[a4audi4fun]

Assuming you are measuring the voltages at the bulb socket, 9 & 10 V would suggest there's still a bad connection (high resistance) between your bulb socket and the battery. What's the voltage either side of where you did your splice? You might also have to trace right back to the Central Electronics module.

[marcrmercado]

That's the voltage directly from the wires in the trunk itself.

[marcrmercado]

Okay, so I used the bulb, socket and ran my own wire as my "test light."

Under the CEM, on the T23, it had the cables going to the 8E0 907 279N, I placed my ground in and started to poke the live wire onto the sockets one at a time.


Everywhere lights up except for a few places and the grey/white and grey/violet (the fog cables [rear]) just happens to be two of them.

Any thoughts?

[marcrmercado]

My battery got discharged the night I was doing the tests so I called it quits after. I had my car jump started and went on with my day. I decided to tackle it again and ran my wires with new ground, and from the spliced, live wire to the other end and I got power on both and after a couple of times getting disconnected, it turned off permanently?

It did the same thing yesterday. A friend of mine who works at a dealership says that these electronically controlled cars can turn off certain thing to prevent damage. I'm trying to figure out how to make this reset again.

[diagnosticator]

All of the tail lamps use fixed pulse width modulation of the power supply voltage to the lamps, to control the brightness of the lamps according to the functional specifications, and to allow adjustment of the lamp illumination power accordingly. Because of this, the measured voltage at the lamps will be lower than +Batt voltage, as determined by the lamp power setting value in % dimming from 100%, in the adaptation channels of the CECM.

CECM Measuring block 006 shows the active power of the rear fogs as currently set in the adaptation channels:

006,3,Fog Light,Rear Left,Display Range: 0.0...100.0 %
006,4,Fog Light,Rear Right,Display Range: 0.0...100.0 %

The adaptation channel and values for the rear fog lamps:

A004,0,Rear Fog Light Dimming
A004,5,Rear Fog Light Dimming
A004,6,Standard: 28 %
A004,7,Range: 13...40 %
;

The CECM will disable certain lamps if there is a short in the wiring harness, resulting in an excessive current load on the CECM. A burned out lamp bulb, results in an open circuit, seen by the CECM as a infinitely high circuit resistance in Ohms. This is fundamentally different from a short circuit to chassis ground. An open circuit results in no current flow in the circuit, whereas a short circuit to chassis ground, (typically, but not always,) results in an excessively high current in the lamp power circuit. Since excessive current will overheat the wiring and damage the CECM, the CECM will disable a lamp circuit having excessive current load, higher than a specified limit, on the CECM. An open circuit results in a burned out lamp warning on the dash insert.

Testing the lamps power supply and ground circuit wiring, requires different methods. The power supply to the lamp socket can be evaluated for continuity and relative resistance between the origin and end point of the wire, and also the resistance in Ohms, measured between the power supply circuit wire and chassis ground. The resistance measured through the wire from the CECM to the lamp socket, must be no more than 1 to 2 Ohms, less is preferred, anything higher implies poor connections in the wiring harness connectors, or lamp socket or a broken wire. . The measured resistance to chassis ground must be open circuit, infinitely high Ohms, more than the meter is able to measure, displayed as "OL" by the meter or similar. However, a resistance value measured and displayed by a DVM, could be less than infinite, of a value in millions of Ohms, or megOhms, that is effectively an open circuit when the applied voltage is low voltage DC as is the case in our cars. Any lower values measured imply a short to chassis ground and must be found and fixed.

For practical guidance, open circuits are a lot more common than shorts to chassis ground, but either type of circuit fault or a duel mode fault can occur as well.

The CECM Diagnostics capabilities can distinguish what type of circuit fault exists. Use VCDS to scan the CECM for fault codes, the fault memory should have fog lamp related DTCs stored.

After the type of circuit fault is revealed by the diagnostics, the troubleshooting steps to find and repair the problem will be focused in the required direction helping avoid wasted time and effort performing tests irrelevant to the specific fault existing.

Ref: VCDS label file: 8E0-907-279-8EC.lbl

[marcrmercado]

I have yet to research into that. I'm sorry I'm taking a while. I work 6 days a week. Anyway, so I left it as is and right now when I unlock the car, the lights power on and the rear fogs flicker then dies.

I lock it and everything powers down. Turn it back on and it does the same thing over. I'm trying to get ideas from an AC electrician which is I know is a different ballgame from DC, and I'm still puzzled and trying to decode diagnosticator's response...

That's like super deep tech language to me.

[marcrmercado]

It's fixed!!! Here is the conclusion of my process:

-When it flicked as it did, I knew that my ground and power contacts were there. I made sure my connections were solid.

-I changed my lightbulb and apparently, it has to be the exact same as the one for your brakes. I've read on a site once about a bulb number that I took in place of it, and it was giving me the flicker-flicker-flicker-off issue.

Thank you everyone for your support!

[B7AudiSline]

Yeah the rear fogs require a double filament bulb so your taillights are still on during normal conditions, but when you activate the rear fogs the other filament lights up. Glad to hear you solved the problem.

[audi900]

It's fixed!!! Here is the conclusion of my process:

-When it flicked as it did, I knew that my ground and power contacts were there. I made sure my connections were solid.

-I changed my lightbulb and apparently, it has to be the exact same as the one for your brakes. I've read on a site once about a bulb number that I took in place of it, and it was giving me the flicker-flicker-flicker-off issue.

Thank you everyone for your support!

What bulbs are you using? my left rear fog light stops working intermittently

[marcrmercado]

7506. Walmart has them for about 5 bucks. Autozone charges a buck more.

Switch your left with your right and see if that fixes your left. If it does, means your bulb is bad. If it doesn't, you have a wiring short.

[audi900]

7506. Walmart has them for about 5 bucks. Autozone charges a buck more.

Switch your left with your right and see if that fixes your left. If it does, means your bulb is bad. If it doesn't, you have a wiring short.

Thanks for your response! I did as you said and switched the left with the right. Still not working, even after I replaced it with the exact bulb. I think it might be a wiring short. I am not savvy with auto electronics so the search begins.. any suggestions on where I should start?

[marcrmercado]

Thanks for your response! I did as you said and switched the left with the right. Still not working, even after I replaced it with the exact bulb. I think it might be a wiring short. I am not savvy with auto electronics so the search begins.. any suggestions on where I should start?

Before all this, test the bulb holder to make sure it ain't the issue by moving it from left to right. Also, check for corrosion between the bulb holder and the socket. If it works, then it's your wiring.

Next, test your ground by getting a volt meter or a "test light." Place the red probe set to 20v onto the gray wire on the working side, and place the black probe on the brown wire. If you got voltage, it's your + wire.

The first time I had this issue, I took it to the dealership. What they explained to me is that it's fairly common for rear lights to go out where the hinges are at. If you look on the left side where the trunk meets the body, what I did for me, is remove the bottom and left trunk interior (check out some DIYs how to do that). Check the color of the gray wire on the malfunctioned socket and it'll have either a white or a violet stripe.

Trace it back maybe a couple inches and cut it. I ran a new wire all the way up and connected it. It'll either work right away or it'll take a few days for it to recognize that it works. Audi tends to kill the switch if it notices the short's been going on for a file and it'll test again to see if it works, so once you're done wiring and you know it's solid... give it a few days before you tackle it again. If that doesn't do it, then it's something else.

Good luck. It's a pain in the ass, but it's so perf now that it works. :.)

[audi900]

Before all this, test the bulb holder to make sure it ain't the issue by moving it from left to right. Also, check for corrosion between the bulb holder and the socket. If it works, then it's your wiring.

Next, test your ground by getting a volt meter or a "test light." Place the red probe set to 20v onto the gray wire on the working side, and place the black probe on the brown wire. If you got voltage, it's your + wire.

The first time I had this issue, I took it to the dealership. What they explained to me is that it's fairly common for rear lights to go out where the hinges are at. If you look on the left side where the trunk meets the body, what I did for me, is remove the bottom and left trunk interior (check out some DIYs how to do that). Check the color of the gray wire on the malfunctioned socket and it'll have either a white or a violet stripe.

Trace it back maybe a couple inches and cut it. I ran a new wire all the way up and connected it. It'll either work right away or it'll take a few days for it to recognize that it works. Audi tends to kill the switch if it notices the short's been going on for a file and it'll test again to see if it works, so once you're done wiring and you know it's solid... give it a few days before you tackle it again. If that doesn't do it, then it's something else.

Good luck. It's a pain in the ass, but it's so perf now that it works. :.)

I will try this and see what I come up with. I was thinking of just cutting the wire where the socket is but it sounds like you went way further down. Where do you get your new wire from??? And thanks for all your help!

[marcrmercado]

Any electronics area like Walmart/RadioShack that carries 18-19 gauge wire. Stranded or solid, it doesn't matter. I wouldn't waste my time cutting it where the socket would be. It would look horrendous like mine since I've done some dumb-a work before thinking.

Remember, test for voltage and test the ground before you dig deep. Removing the interior will require torx bits and a 10mm socket. (Takes 5 minutes, 15 if you're new to it.)

[audi900]

Any electronics area like Walmart/RadioShack that carries 18-19 gauge wire. Stranded or solid, it doesn't matter. I wouldn't waste my time cutting it where the socket would be. It would look horrendous like mine since I've done some dumb-a work before thinking.

Remember, test for voltage and test the ground before you dig deep. Removing the interior will require torx bits and a 10mm socket. (Takes 5 minutes, 15 if you're new to it.)

Haven't had time to trace the wires yet. Before, my left rear fog would work only when the trunk was halfway open or in the "sweet spot" kind of like the same issue you were describing earlier. Now it has COMPLETELY failed and doesn't turn on at all. Do you think it could have anything to do with the light switch? Just want to check all possibilities before cutting anything. Thanks for any responses.

[audi900]

Finally got a chance to follow marcrmercado's advice and instructions. I must say thanks. Everything is working 100% now!

[marcrmercado]

Of course. Have a good Monday.