It's dark outside
 

Regarding a 2010 997.2 C4S with standard (not auto adaptive) headlights...

A friend's headlights quit working. No low beams. No high beams. But the high beams do operate via the flash feature on the stalk.

Fuses appear good. DRLs work. Parking and rear fog lights work from the switch. Just no headlights.

I swapped light switches with my car to no avail.

Looking at the schematic it looks like the lights are controlled by the front module via the CAN bus. So why does the flash work (indicating power to the control module and connection to the CAN bus) but not the switch?

Any thoughts?

As an aside, the static battery voltage read low but when running the charge voltage looked fine. The CTek indicates yellow with inability to achieve green even with extended charging time. We replaced the battery today. This probably doesn't have anything to do with the headlights, but ...

Additionally the TPMS just started reading 0, 0, +2, +2 (delta pressure?) instead of absolute pressure. I believe this is an option for the readout but haven't checked the Manual or my car on this. Just adding this here as a possible data point.

BTW, the 997.2 has a very neat light switch removal ...

1. Turn to the off position.
2. Push in on the switch.
3. Rotate clockwise (not quite to 12 o'clock).
4. Pull it out.
5. Unplug the connector.

Literally less than 15 seconds total!!!

Thanks in advance for any advice.

Wayne, you say you replaced the battery... then what? Low battery voltage causes all kinds of problems in these highly digitally-controlled cars. I wonder if the issue is a system reset due to low voltage or a short circuit caused by some rodent (Yikes!).

The change of the TPMS readout from absolute to relative is an indication of a system reset. One can choose the absolute or relative display option.

Thanks for the info re light switch removal. Much easier than others I know.

Tony ... Yep, my thoughts on the low battery and the change from absolute TPMS to relative.

Doclouie ... I was surprised about the lack of a relay, but the front control module appears as a black box in the schematic. The location is supposedly at the front right of the frunk but when I peeled back the carpet I didn't see anything. I suspect there could be an N channel (or less efficient P channel) FET controlling the bulbs, but I can't tell. I still would expect the high beam flasher not to work from what the schematic indicates. All of these functions appear to be CAN bus based and thus tied together.

The last thought is the headlight switch (via CAN bus) needs to be reactivated via PIWIS. As Tony said, a low battery can cause havoc 8(

Thanks for the responses. Now I need to grab my headlight switch out of the truck and reinstall it. Time to go for a drive 8)

In the meantime, this may be something for the dealer. I'll let you know when we find something.

My bet is that the system reset itself improperly and needs a PIWIS review, now that a new battery is in place.

Don't know the answer, but will a Durametric Pro do the job in lieu of the PIWIS?

It's worth a try.

Wayne - Pat reset my ECU into "delivery mode" to clear out a wonky fault I got with my heated seated after disconnecting the battery. He had to do the same to fix my front control module. They arent open today but swing by Sonnen and we can do a quick loop on the 1 back to Stinson :-)

The Bruce ...

It's not my car that's affected. But I always enjoy visiting Ryan in Parts and the Stinson ride is always welcome!!!

The headlight control is in the front controller, where you mentioned problems. So this may come down to a marginal battery (now replaced) and the need for a reset. It's the only thing that makes sense to me.

These computers seem finicky from what I've read. I'm not sure why the system can't auto populate and adjust. I need to learn more about the CAN bus!!!

Wait ... makes me think ... people have mentioned a problem with static discharge affecting the front controller when cleaning the bumper. Isn't that what happened to yours? Hmmmm.

As an aside, as I've cut down to four, then three, then two, then one, and after Tuesday no days a week working I'm discovering mine sits in the garage for days at a time. It may be time to break open the packaging on my battery maintainer and make sure it works. Or better yet, take daily pleasure drives 8)

I had that problem on my 996 driving from Montana to CA. Night came and no headlights. However, like you described, the high beam flasher worked. Drive for a couple of hours with the high beam flasher pulled back which illuminated the road quite well.
It turned out to be a bad relay in the lever assembly which I had replaced. No problems after that (excluding the IMS failure a year later, which is why I'm now on the 997 forum).

Thanks for the report and sorry to hear about the 996 woes.

Your problem sounds identical. Sorry for being stupid, but what and where is this lever assembly you spoke of?