Another pesky Prius 2 headlight problem

2008 Prius 2, first owner, 50Kmi.
The car has developped an intermittent problem with the driver side headlight. Turns on fine, but turns off after about 30 seconds. Turns back on if the lights are toggled off/on. Sometimes took a couple of retries on the light switch to "fully" turn on.

First, the bulb got changed by the dealer at their own initiative at the occasion of an oil change. Different bulb model, clearly warmer temperature, but problem still present.

Then I decided to go after the ballast. Ordered a replacement ballast, followed a DIY to take the headlamp module out, swapped the ballast with the new one, remounted, everything seemed fine. For a few days at least.

Now the headlight turns off again after 30s. Observing the symptom closer:
- when cold (first attempts), the light flickers several times and fails to turn on

- after a few tries, the light stays on 30s, then flickers before going off

- if I toggle the headlight switch, it goes back on, etc ...

Passenger side running fine. Original ballast and bulb. No problem.

My next move in consideration is to swap the bulbs to see if the bulb+ballast combination is marginal, and the OEM bulb will run fine with the new ballast, while *maybe* the new bulb runs fine too on the OEM ballast (or I can limit further actions to finding another colder D2R bulb).

Before I go through the joy of swapping the bulbs, I would like to know whether there are possible other upstream root causes i am ignoring.

I don't see how the ECU could be responsible. If i understand the schematics correctly, the relay toggles the power that goes to both headlights, so the problem can't be there.
Could a brand new ballast be defective ?
Could the warmer D2R bulb installed by the dealer be incompatible with the ballast ?

Many thanks in advance for advice or insights. This car has been really reliable, but this problem is a safety concern.

 

So i have done my bulb swap:
- side which works, OEM bulb: OSRAM Xenarc D4R 66450
- side which does not work: Philips D4R XenEco 42406

After swapping, the problem follows the Philips D4R, so that bulb is not compatible with the OEM ballast.
Ordering a replacement OSRAM bulb.

 

I wrote D2R in my first post by mistake, I have D4Rs.
But the fact is that, on this 2008:
- OSRAM Xenarc is/was OEM
- the replacement Philips Xeneco my dealer installed challenge the ballasts, both original and replacement, to the point of malfunction.

 

Yes, the headlights are OEM, nothing's been changed, and it shows no haze at all. Car is bone stock. Surely gets less sun than if it was parked outside in a warm climate.

I will have to differ with you on the bulb:
1) the driver side ballast is brand new. It works fine with the OSRAM Xenarc, but doest not work repeatably with a 2m old Philps Xeneco
2) the passenger side ballast is original (2008). It works fine with the OSRAM Xenarc, but does not work at all with the Philips.
3) OSRAM Xenarc is the original equipment, not Philips (in this car)
4) the Philips Xeneco has a completely different temperature and far lower intensity than OSRAM

Admittedly, I am just looking for a solution since I am sellling the car anyway, and yes, that Philips bulb, though 2m old in its 150$ glory, could be marginally defective, have excessive impedance. I am not too sure what else could have an influence. Control signal drives the ballast, ballast drives the bulb.

I just got a 2nd OSRAM Xenarc so I'll be able to confirm my observations and deliver the car.

 

OSRAM Xenarc swapped in and everything back to normal.
So on this car and FWIW, Phlips Xeneco can challenge an OEM ballast, old or brand new.