2005 Subaru Headlights and Oxygen Sensors

Ray and Tom once took a question about a 2005 Subaru owner who keeps burning head lights… they blamed in the person touching the headlights… I hate to say they are WRONG… a search on Google yields many discussions regarding this issue… and it is an issue I also suffer from. My 2005 Subaru burnt out multiple headlights and Oxygen sensors under warranty… Subaru never acknowledged an issue… I have stopped replacing the Oxygen Sensors and I burn out 4-5 sets of headlights a year (and I do not touch the bulbs). So does anybody have an idea on what to do about this problem?

What’s the battery voltage with the engine running and all accessories off?
Should be 13.5-14.5V.

The only fault with our 2005 Subaru Legacy turbo wagon with 77k is burned out headlights at 20k miles. The dealer replaced under warranty both and not a lick of trouble.

The o2 sensors failing repeatedly indicates a problem that is not the sensor itself but somewhere else and damaging them.

When checked by the shop it was 13.5 volts with the engine running. As another part, when a headlight burns out, the other burns out within 2 weeks… I figure that is part of a surge when the one head light burns out… also the only lights to have burned out are the low beams…

Was that voltage only at idle, or did you also test it up through the entire rpm range to make sure it doesn’t increase?


They did ‘Rev’ the engine but my no measure was it carefully done… and they indicated it always was “around” 13.5 volts so I take that as it remained within normal operating parameters and did not throw a flag up to them.


My '02 Outback, with over 97k on the odometer, still has the original headlight bulbs, and its original o2 sensors.

One tail light bulb did burn out a year or so ago, but other than that, the only parts that have been replaced in the 7 years since I bought it are the idler pulley and the tensioner for the serpentine belt. The bearings in both of them were starting to get noisey for the first few minutes after start-up on a cold day. Apparently this is an issue with the H-6 engine, after 90k or so.

The 2005 design had something different on headlights from previous generation.

Not even a single CEL my entire ownership. Trouble free car

You have checked the DC voltage but you should also check the AC voltage. Bad diodes in the alternator can cause excessive AC ripple. With the engine running around 2,000 RPM you shouldn’t have more than .1 volt of AC voltage across the battery.

When an electrical circuit is turned ON, or OFF, a voltage surge occurs each time. These surges can shorten the life of the light bulbs (or, other things). The electrical circuit can be rapidily turned on and off where there is a poor electrical connection. A couple of places this could happen is in the alternator, and the highlight relay. There are other connection places. The quickest way to detect if this is happening is with an oscilloscope connected to the headlight circuit.