I posted a while back on a friend's headlights. The problem was that the headlights would not turn on, at all.

All fuses are good and all other lights function correctly.

The schematics I have imply that there is no relay and that the control comes from the front control module via the CAN Bus (FET drive via a logic input?).

As it stands now ...

New battery, in good condition.

The car went to an independent for a computer reset. They also unplugged and plugged in the front control module connectors (there's no such thing as a good connection ...).

And now, when the ignition is on, the headlights operate whenever the light switch is in the off position but shut off whenever the switch is in the on position.

All other lights behave properly (parking, DRLs, instrument, brakes, turn signals, etc.). Even the high low beam works (as long as the light switch is not asking for headlights).

It's like someone installed an inverter to the headlights. I flipped my light switch with the other car. The problem is with the car, not the switch.

Is there a PIWIS reset or something that may fix this? The original battery had gone weak but not dead.

I'm confused ...

 

 

Interesting..... how hard is it to get at that front control module.... that is all that is left no? It looks to me like you have to pull the front bumper off.... from inside the trunk? Its a 997.2 no? If a 997.1, folks were swapping the headlights out and required electronics... any evidence of this work and its reversal?

Nothing I am aware of re the Durametric... but that tool is so poorly documented, who knows?

Peace
Bruce in Philly

 

Have you tried a 10 min battery disconnect just for fun. Was the car being detailed before this problem happened Static from polishing or wiping the hood bumper or headlights has been knows to build up enough static to fry the front control module, but you usually get the lightning bolt error on the dash screen after it happens.

Does the 997. 2 have an auto position for the headlight switch like the Cayenne from the same generation or is it just like the 997.1 version. If it has an auto position, what do the lights do when set there.

 

Not an expert but just my thoughts, Reversal of the on/off control isn't a programmable parameter unless your savy enough to decode the firmware, so I don't think this is a software issue. If you had an scope with can interface you could decode the inbound message to make sure it is correct but this is way out of the realm of most people.

Typically in most control circuits, the CAN is decoded by a microcontroller, then sends low level complementary signals (ie one positive and one negative) to some kind of FET bridge with an upper and lower fets which then turn on and off the actual lights. Given you have a CAN message making it over to the module but resulting in inverted logic, it does suggest your headlight controller module. I would also just check to make sure all inbound/outbound connections on the module have continuity to where they are supposed to go to.

 

Thanks for the input.

It is a 997.2.

We swapped headlight switches with my near identical 997.2 and the problem stayed with the other car (my car still worked fine with the other car's switch).

There is not an auto switch on the 997.2 ... off, parking, home, on. The headlights turn on with the ignition if the switch is at off or parking. They turn off at home and on.

Static damage had been considered. Saw this happen to a friend's 997.1 when his wife brushed against it with her yoga pants. We have not flip flopped the control box. That move makes me a bit worried ... concerned a wiring problem in the other car could subsequently damage my box.

Interesting thought on the complimentary signals. I do have an o-scope but I wouldn't have a clue if the signal I was looking at was valid or not!!! I've tracked down a lot of RS232 comm signals and have ultimately found (short of signal degradation or driver problems) computer data capture to work better than a scope for analysis.

Note: Now that I've converted from full time to consulting status I hope to find time to get smart on CAN Bus, but that will have to wait until I finish remodeling the house for Pam.

The Indie wants to run a parallel wire when he has time. My schematics don't show that wiring detail. But the guy is very good so it looks like that is the next step.

Again ... Thanks for the thoughts 8)

 

Have you tried using a scope probe at the actual input to the headlight module to see how it toggles or latches (ie to a fixed dc voltage) after you turn on the headlights. Curious if you could compare the two waveforms on the good car verse the bad car. That will help isolate to the headlight module.

 

Interesting thought, comparing cars side by side that way. Thanks.