How Does It Know?

"Dakotahound" (dakotahound)
08/28/2020 at 10:06 • Filed to: Porsche, Boxster, Boxster 987

This morning, my 987 Boxster illuminated a warning message, “Check front left side light.” I checked the light, and everything seems fine, but I have reason to believe that the front left side light will soon need replacing.

Porsche 987 Boxster warning light.

Over the course of the past two years, I have replaced both dipped beams (low beams) and one side marker (actually, I replaced both side markers, but only one was out). About three weeks prior to each one failing, my Porsche gave me a warning. How does it know? I have some ideas:

1) The resistance of the bulb changes slightly before it burns out.

I don’t think that this is the case. The resistance of the bulb would normally change due to weather (hot and cold). Also, consider the case when the light has been on for a while and then the car is restarted. The bulb would be hot (with high resistance) during the start-up test.

2) The bulb becomes intermittent just before it fails.

This seems more likely. In fact, during the three weeks prior to the light failing, the warning is not constant. I get it about every other day, and it goes out after I drive a few miles.

3) This is a totally random event.

Not likely.

(This picture also made me realize that I need to clean my instrument panel.)

DISCUSSION (24)

WasGTIthenGTOthenNOVAnowbacktoGTI > Dakotahound
08/28/2020 at 10:16

It knows because it puts up the warning, and if you don’t replace it, it turns itself on a t night and breaks the bulbs itself.

The Snowman > Dakotahound
08/28/2020 at 10:17

Combo of 1 and 2. It's intermittent but caught by a resistance test.

Tripper > Dakotahound
08/28/2020 at 10:18

Maybe a time based setting that is hilariously accurate?

My 96 explorer had this feature (not the predicitive one but the “front left light out”) in typical ford fashion the light was fine, it was the control module that tells the car the light is out...it failed so the lights go out...

nerd_racing > Dakotahound
08/28/2020 at 10:21

This is just the pre-warning. The over the air courtesy alert. If the bulb is not changed in the time allotted , they send a G erman to your house to deactivate the bulb manually.

Dakotahound > WasGTIthenGTOthenNOVAnowbacktoGTI
08/28/2020 at 10:23

At least that guarantees it is correct.

phenotyp > Dakotahound
08/28/2020 at 10:23

It’s a German car-- the warning lights come on automatically.

Dakotahound > Tripper
08/28/2020 at 10:24

Well, I’m not sure that mine is predictive, but it sure seems so.

Dakotahound > nerd_racing
08/28/2020 at 10:25

Now that you mention it, there have been strange noises coming from the garage.

Dakotahound > The Snowman
08/28/2020 at 10:25

That is possible, I just didn’t think it was that smart.

WasGTIthenGTOthenNOVAnowbacktoGTI > Dakotahound
08/28/2020 at 10:29

Vee Do not make Mistakes!

Dakotahound > phenotyp
08/28/2020 at 10:29

This is slightly different but, about a year ago, my PSM light came on intermittently. I could not find the problem and, when I gave up, the Porsche dealer tried but had no luck. In some online forum, someone mentioned that the brake light switch can cause the PSM failure. I asked the Porsche dealer about it, but they said it was not possible. I went ahead and replaced the brake light switch anyway , and the problem disappeared.

phenotyp > Dakotahound
08/28/2020 at 10:35

That’s actually way better than my E60s-- with those, shit would just fail without warning. The best is when the water pump crapped out, the first warning I got was the “STOP DRIVING-- THE CAR’S GONNA EXPLODE” warning screen as it went into limp mode.

Merkin Muffley > phenotyp
08/28/2020 at 10:45

I was shocked to figure out the M60/62 engines in my 5-series have all the vital fluids circulated via the serpentine drive belt. A belt or tensioner failure gets you an overheated set of heads RIGHT NOW.

By contrast that “antiquated” LT1 in my Roadie wagon drives the water pump with a SOLID drive pin directly from the cam in block. If the pump stops turning on that Roadie you have bigger problems because the cam’s not turning either.

It's funny to see how the BMW design ideal is immensely complicated in the primary order... but somehow built with the idea that no components ever fail.

AMGtech - now with more recalls! > Dakotahound
08/28/2020 at 10:53

That’s exactly it. Power doesn’t get to the bulbs directly from the fuse and light switch. They’re all powered through a module that monitors current flow on the circuit. It knows what a normal resistance range is, even with temperature changes. It’s more looking for a lack of current flow. Often when bulbs fail, their filaments will burn open at one small point , then collapse and make contact again and continue working for a time. This can happen so many times that the glass of the bulb turns black and the filament looks like the burned out carcass of an old abandoned barn. If the filament isn't is perfect condition, or if the glass is slightly smoky, just replace the bulb.

phenotyp > Merkin Muffley
08/28/2020 at 10:55

“but somehow built with the idea that no components ever fail”

Perfectly stated.

CalzoneGolem > AMGtech - now with more recalls!
08/28/2020 at 11:34

Probably if you’re going through all the trouble to look at the bulb you should replace it

This is what we'll show whenever you publish anything on Kinja: > Merkin Muffley
08/28/2020 at 11:35

And then they use polymers that are designed to fail.

Merkin Muffley > This is what we'll show whenever you publish anything on Kinja:
08/28/2020 at 11:36

Yeah. I totally concur. Where do they source their terrible plastics? And.... Why?

Jb boin > Merkin Muffley
08/28/2020 at 11:40

You usually can’t drive long without a serpentine belt (or that is slipping violently) on a gasoline engine and most probably would hear/feel something is wrong and stop the car quickly .

This is what we'll show whenever you publish anything on Kinja: > Merkin Muffley
08/28/2020 at 11:42

So those who can afford them go buy another new one and the poors who buy used bankrupt themselves.

Merkin Muffley > Jb boin
08/28/2020 at 11:57

On an LT1 or LT4 you lose alternator and power steering... but with a full battery you can drive a hundred miles or more to safety.

In a BMW you get eaten by rabid armadillos.

Dakotahound > AMGtech - now with more recalls!
08/28/2020 at 12:04

I didn’t know that bulbs did that - thank you. I guess it would be harder to predict LED failures ( of course, they don’t fail nearly as often).

MiniGTI - now with XJ6 > Dakotahound
08/28/2020 at 13:04

#2 has happened in my MINIs a time or two over the years.

AMGtech - now with more recalls! > Dakotahound
08/28/2020 at 13:51

LED's still have current flow and can be monitored in the same way. But if they don't have a built-in resistor they will set a warning if used in place of a standard bulb, because the two types have different current flow. Lots of new cars use LED's from the factory and do a perfectly fine job of monitoring them. Many of those stop working from getting hit though.