07 S550: is it on fire?

[kevm14]

Yeah it was scary.

Was driving to work last week and was still in my neighborhood when I began to smell something off. I thought maybe it was wood stove related but I kept driving and it kept getting worse. Then I noticed wisps of smoke coming out of my dash, on the right side near the base of the windshield.

It was coming from the area circled, roughly:

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The defroster vent ends before the edge. I kept driving and it kept getting worse and I'm now thinking, if I don't pull over and shut this off, I may lose the car. I couldn't pull over where I was but I instinctively turned off the rear defrost and HVAC. Another 30 seconds later and it seemed like the smoke was subsiding. I decided to chance it and just drive to work even though I was less than 5 minutes from home.

This turned out to be fine because the symptom never returned. The car doesn't smell like burning, there is no smoke, EVERYTHING works, no codes in the modules. It's pretty baffling. I thought maybe the HVAC fan was smoked but that is clearly not the case.

I have narrowed the cause down (just logically) to the heated wiper park position feature. It is what it sounds like, a hidden defroster grid at the base of the windshield where the wipers park. My window sticker claims this was a standard feature. I also examined the fuse (30A) and relay for this and everything seemed fine, with no melting or other suspect evidence.

I have driven the car a number of times with full use of the fan and rear defroster and the symptoms did not reappear. This morning I connected DAS to play around. It does appear that I have this feature and while the control side seems to work fine, there is no de-icing occurring.

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So I'm thinking something just fried and is now open circuit. There are also two possible codes related to this feature and I have neither of them.

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These codes only check the output of the relay which means the control side, the power supply fuse and relay are all working. It doesn't know anything about the load side (although the front SAM absolutely measures load current on many circuits, just not this one apparently).

While this was scary, this is really the best possible outcome. I just lose a feature that I didn't know I had and my car is safe to operate.

I probably could pull the front SAM cover again and measure the resistance of the heating element at one of the fuse or relay pins to ground but I'm betting it is open circuit for all of the reasons I explained above. To draw up to 30A it would need to be as low as 0.4 ohms but is probably made to draw more like 20A so perhaps 0.6 ohms. FWIW I also found no mentions of this on the forum so this is quite uncommon.

Fun fact: the heated windshield (that my car does not have) is run at 42V, presumably due to current limitations of the various system components. You know, to prevent fires.

Self-inflicted but self-healing and fixed forever?

[kevm14]

Coded it off easily with the Launch X431.

Verified removed in DAS where I can't even show the status of the system (because it's been coded out).

So the car will never try to actuate this system again. I guess if I ever see smoke or smell something again, it can't be this system.

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[kevm14]

I probably could pull the front SAM cover again and measure the resistance of the heating element at one of the fuse or relay pins to ground but I'm betting it is open circuit for all of the reasons I explained above. To draw up to 30A it would need to be as low as 0.4 ohms but is probably made to draw more like 20A so perhaps 0.6 ohms. FWIW I also found no mentions of this on the forum so this is quite uncommon.

In case I want to do this check later, here is the schematic for the wiper park position heater.

Position 40L on diagram, component R2/10. I would check continuity between one pin of the fuse and chassis ground. I'm betting this will be open circuit.

[kevm14]

So here's a wild theory.

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Could my windshield have cracked and split the wiper defroster causing some kind of gap which then caused some smoke due to high resistance? Maybe it just took this long to finally expose itself and climb out of the black tint area which probably does hide it.

Or the defroster overheating caused the crack. These may well be related. It is in the exact same area that I saw the smoke.

[kevm14]

Just for posterity, I have circled the crack location in orange on top of the old photo with the blue circle showing the approximate area of magic smoke. It's the same area.

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