sseiyah

2008 Lexus LS600h L

Here is a video of the headlight behavior, the key fob was about 20 miles from the car when this was recorded and the car was unlocked:

You Tube

I have a strange headlight and taillight issue I have been unable to figure out. After I park the car the headlights and taillights will randomly turn on and off usually every 4-8 seconds. Eventually the lights will stay on after the lights flash hundreds of times which takes anywhere from 30 minutes to a couple hours. I'm not sure what to try next to fix this problem. I thought maybe the relay was sticking but since the issue occurs only with the ignition is off I'd think the relay is fine?

So far I have tested the 4 door switches for continuity with no issues found. I replaced the drivers door switch for good measure but there was no change in behavior. The Panasonic 12V battery was recently replaced and I just had it tested again yesterday and no problems were found.
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• The problem does not occur when the ignition is ACC or ON Mode, the headlights and tail lights work as designed in this mode.
• The problem does occur when the headlight switch is set to Off or Auto, no difference in behavior.
• The headlights and taillights will not respond to the headlight switch once they get "stuck" on however putting the ignition in ACC or ON mode will turn them off if the headlights switch is set to off. They stay off but then start flashing again like shown in the beginning of the above video.
• The problem does not change whether the doors are open or closed. Same behavior either way.
• The problem does not change whether the doors are locked or unlocked.
• The problem occurs in broad daylight and when its dark.
• In Tech Stream I changed Light Auto OFF Delay from 30 s to OFF and there has been no change
• DTCs are unchanged from before this problem started, no new DTCs logged.

jmcraney

You should check to see if your spare wireless-electronic-key is caught in your seat. Run your hand through the part where the backrest meets the seat bottom.

Gerf

In Techstream under "Electric Power Control" in the data list you can watch the condition of the light combination switch, I've never seen this problem before but if it's switching while in the off position that's not a good thing haha...there must be a lighting control module as well somewhere.
I would check for water intrusion in the trunk and footwell areas too.

jmcraney

If this is being caused by a “rogue key” it will cure iitself when the key battery is depleted,

dan25man

It's a ghost. Lexus well is known for incorporating parts of past Takumi's into their cars. Thats why the LS's feel and drive like old men (because they are!) I think there's a TSB out there somewhere for the spirit induced electrical problems. Ask your local Lexus dealer.

Boykie

Spirit of mt.Akina? Or Bunta's?

sseiyah

I changed out the headlight multiplexer module next to the under-hood fuse box but the symptoms did not change. After a long drive yesterday the problem changed. The car stopped turning the headlights on at random with the car off and now turns them off when the ignition is off. The new problem is now the headlights stay on when the ignition is set to Accessory or On regardless of the headlight switch position. I tried running the Head Light Low Beam test however it fails. "ECU cannot perform the requested Active Test. Please verify that all vehicle conditions are met and try again."

The headlights do not turn off when the ignition is on with the headlight switch disconnected. They just stay on.

I will install a replacement headlight switch soon and see if that corrects the issue.

Marc780

Well, let's think on this for a minute and ask, what other circuits affect the headlights? The obvious answer would be the ignition switch. Not sure how you'd isolate the ign even for testing, but probably by pulling a fuse or two. But if you can disconnect the ignition completely, while still keeping power available to the headlights, I'm thinking this definitely would have to affect your headlight problem. And if it does, fix might be a new ignition switch (which you obviously don't want to rush into buying just on the off-chance that might be the problem).

swfla

iTrader: (1)

The daytime sensor for automatic lights on at dusk is another circuit that could be the cause. It’s forward and center on the dash. If you can turn off this feature, it may help diagnosis.

Marc780

So OP how did you finally fix the problem? What turned out to be the cause?