Brake pad warning + light

[MacaveliMC]

Hey guys,

Wanted to get your thoughts on what is happening here. For the first time since I bought my 2012 B8 S4 a year and a half ago, I started it up and the brake pad symbol + the brake light on the dash came on. But if I turn the car off then back on, they usually go away.

Am I understanding that both of these lights coming on typically means that it's probably time for brake pad replacement?

Here's the other part of the story:

A little while ago, I was doing some work on the car and I noticed there was a connector under the front driver wheel well with a pigtail or modified connector of some sort plugged into it. It seemed like it would be for the brake sensor wire, but it wasn't going to the brake pad. Instead it just had the pigtail or modified connector plugged into it.

So in my mind, someone didn't wanna deal with brake pad warnings and just plugged in a dummy connector to trick it? But then how am I now getting brake pad warnings? Also, am I right in believing there is only one of these connectors on the front driver side? or is there 1 for all 4 wheels?

These are just my initial thoughts before I have the time to actually go look into it by removing wheels, but I wanted to get some thoughts from the forum in case there is something I don't know or am missing.

Thanks!

- Mike

[Gunnark100]

Elsawin also shows on s4 2012 right front and right rear have sensor - but it is written optional - so do you have or not - i do not know!

[MacaveliMC]

Elsawin also shows on s4 2012 right front and right rear have sensor - but it is written optional - so do you have or not - i do not know!

Does it show both as option or just one of them?

[Gunnark100]

Does it show both as option or just one of them?

both right ones are optional, but in your case it does not matter, as they connected in line and left front one is last, so your light is on, due faulty dummy connector or cable is faulty between dummy connector and j519.

[sepheroth86]

both right ones are optional, but in your case it does not matter, as they connected in line and left front one is last, so your light is on, due faulty dummy connector or cable is faulty between dummy connector and j519.

This is good info.

How does one test the circuit?

[Smac770]

Wiring diagrams for B8.0 show only the G34 front left brake pad wear sensor. B8.5 show the optional G35 front right and G37 rear right brake bad wear sensors.
Parts catalog seems to show no indication of a pad wear sensor cable/plug for anything more than inner front left pad for B8.0 or B8.5.

If you wanted to test the sensor, unplug it and test for continuity across the two pins of the sensor side plug. When the sensor breaks, it breaks the circuit.
If you wanted to test the complete circuit path, you'd need to get to the J519 under the dash behind the headlamp switch. Unplug the T32B plug (black) with the black wire in pin 9 and either 17-pin plug (brown or red) with the large brown wire in pin 17. Then test for continuity between the T32B plug pin 9 (black wire) and either 17-pin plug pin 17 (large brown wire). The final ground point for all of those ground wires is the chassis ground point at the base of the a-pillar behind the kick panel.

[sepheroth86]

Wiring diagrams for B8.0 show only the G34 front left brake pad wear sensor. B8.5 show the optional G35 front right and G37 rear right brake bad wear sensors.
Parts catalog seems to show no indication of a pad wear sensor cable/plug for anything more than inner front left pad for B8.0 or B8.5.

If you wanted to test the sensor, unplug it and test for continuity across the two pins of the sensor side plug. When the sensor breaks, it breaks the circuit.
If you wanted to test the complete circuit path, you'd need to get to the J519 under the dash behind the headlamp switch. Unplug the T32B plug (black) with the black wire in pin 9 and either 17-pin plug (brown or red) with the large brown wire in pin 17. Then test for continuity between the T32B plug pin 9 (black wire) and either 17-pin plug pin 17 (large brown wire). The final ground point for all of those ground wires is the chassis ground point at the base of the a-pillar behind the kick panel.

Would this also apply for a C7 A6?

[MacaveliMC]

Wiring diagrams for B8.0 show only the G34 front left brake pad wear sensor. B8.5 show the optional G35 front right and G37 rear right brake bad wear sensors.
Parts catalog seems to show no indication of a pad wear sensor cable/plug for anything more than inner front left pad for B8.0 or B8.5.

If you wanted to test the sensor, unplug it and test for continuity across the two pins of the sensor side plug. When the sensor breaks, it breaks the circuit.
If you wanted to test the complete circuit path, you'd need to get to the J519 under the dash behind the headlamp switch. Unplug the T32B plug (black) with the black wire in pin 9 and either 17-pin plug (brown or red) with the large brown wire in pin 17. Then test for continuity between the T32B plug pin 9 (black wire) and either 17-pin plug pin 17 (large brown wire). The final ground point for all of those ground wires is the chassis ground point at the base of the a-pillar behind the kick panel.

So I only have front left since I have a B8. Do you know, is there anything else at all that can cause the brake pad warning + the brake light besides that circuit being broken?

[Smac770]

So I only have front left since I have a B8. Do you know, is there anything else at all that can cause the brake pad warning + the brake light besides that circuit being broken?

The J519 applies voltage to the wire on T32B pin 9. If it detects current flow, it knows the circuit is complete, meaning the pad wear wire is not worn through. If it does not detect current flow, then it presumes the wire is worn through and it advises the instrument cluster of such. So there's any number of points along the wire path where an issue could occur. Could be the wire, could be at the plug between the wheel well harness and the sensor, could be at the splice of the wheel well harness to the vehicle harness. But that's the only involved component to the J519 deciding to set that light or not.

Some pics of the sensor: https://www.fcpeuro.com/products/aud...q5-8k0615121-1

[Smac770]

Would this also apply for a C7 A6?

I don't have documents for C7 platform since I don't own one. But if we look at the parts catalog, we see one wear sensor on the front and on the rear. The B9 uses front left + rear right. I presume that's the configuration on the C7 as well. Unless you have the ceramic rotors. In that instance, it appears you have a sensor at all four corners.

[Gunnark100]

Wiring diagrams for B8.0 show only the G34 front left brake pad wear sensor. B8.5 show the optional G35 front right and G37 rear right brake bad wear sensors.

Correct, i typed 2012, but in EU it is b8.5 already.

- - - Updated - - -

Would this also apply for a C7 A6?

give me year and engine i will check

[Gunnark100]

The J519 applies voltage to the wire on T32B pin 9. If it detects current flow, it knows the circuit is complete]

It is simple 0.5 ground wire, so j519 does not apply voltage, but receives ground signal!

[Smac770]

So you won't see the + on the wire as the sensor loop is not the voltage drop location. It's using the line as a ground to an internal test circuit instead. Ok, no doubt more reliable that way. Explains why people just short pin 9 to ground with no need for a resistor when they eliminate the sensor with certain brake configs.

[Smac770]

That being the case, to test if the circuit is whole, you only need to test the voltage from any 12v source (such as the term 30 fuses on that end of the dash) to that pin 9, 12v good, no volt bad.

[sepheroth86]

Correct, i typed 2012, but in EU it is b8.5 already.

- - - Updated - - -



give me year and engine i will check

2012 A6 3.0t Prestige North America market.

[Gunnark100]

2012 A6 3.0t Prestige North America market.

I cant take pictures out from my new VM, hopefully you can downloud and use zoom.

[MacaveliMC]

The fact that I have a dummy plug on mine leads me to suspect maybe a change has been made to the brakes? Why else would you put a dummy plug on with OEM brakes? Who doesn't wanna know their brakes need to be changed? I should take a picture of the brakes and post a pic on here, maybe you guys can tell me if they are stock. Don't wanna buy new pads or other and find out they don't fit.

[Gunnark100]

The fact that I have a dummy plug on mine leads me to suspect maybe a change has been made to the brakes? Why else would you put a dummy plug on with OEM brakes? Who doesn't wanna know their brakes need to be changed? I should take a picture of the brakes and post a pic on here, maybe you guys can tell me if they are stock. Don't wanna buy new pads or other and find out they don't fit.

Yes, your pads have been changed, as it is already 10 years old car :). Probably wire has damaged somewhere, thats why they put dummy there. Many people change rotors and pads together and light will be on to soon, still 20-30% pads wear left. So maybe previous owner did economic decision or for sale - who knows...

[blackfunk]

Car could have also had a BBK installed. I've thought about coding mine out but I've gotten so used to staring at that red light I figure I'd miss it too much. Either way its best practice to check your brakes yourself at least twice a year.

[MacaveliMC]

Car could have also had a BBK installed. I've thought about coding mine out but I've gotten so used to staring at that red light I figure I'd miss it too much. Either way its best practice to check your brakes yourself at least twice a year.

Any quick way to know looking at them if they have the BBK or not?

[Smac770]

BBK = big brake kit, ie just some oversized aftermarket arrangement. Not sure just using a larger OE brake option constitutes a BBK. As for what are your rotors, just measure them. Either they are the expected size per your PR code or they are not.

Prior owner probably used a brake pad set that didn't have the sensor, or he didn't want to buy the sensor.

[blackfunk]

Using something like this - https://www.audizine.com/forum/showt...1#post14778614

A plug or terminating the sensor is typically the only option. Mine was terminated for a few years and somehow got loose but just haven't been inspired to resolve again.

[hardfive]

Theyre dummy plugs for sure. Have them in my car as i have a bbk and didnt want the stupid light on. Previous owner had a brake kit.

Post a pick. Stock brakes pretty obvious.

ECS sells them. https://www.ecstuning.com/b-ecs-part...BoCQp8QAvD_BwE

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