1994 940 Bulb Out Warning...but no bulbs out...

Pianoman702 · Post by **Pianoman702** » 20 Jun 2012, 22:06

Today when I started up my 1994 945, the "bulb out" warning light came on. I got out of my car and checked every light that would trip the sensor: Parking lights, headlights, and tail-lights (I can eliminate brake lights because the light is permanently on). Every single light worked.

Curious, I moved the light switch to "parking lights" and the warning went away. I moved it back to headlights and the warning came back on. Then I pulled the high-beams and the warning went away. Thinking I skipped over one of my headlights, I checked again and both were working.

What could the problem be?

Could I have somehow fried the bulb out relay?

Post by **jimmy57** » 20 Jun 2012, 22:33

Sometimes the filament cracks and then arcs and fuses itself together again. This is enough imbalance to make the bulb light come on. I bet you'll have a low beam out soon.

Pianoman702 · Post by **Pianoman702** » 20 Jun 2012, 23:20

I'll hold you to that, Jimmy!

In the meantime, if I were to go to a junkyard, should I get an extra relay?

lummert · Post by **lummert** » 20 Jun 2012, 23:47

I'd get a light switch.

Pianoman702 · Post by **Pianoman702** » 21 Jun 2012, 00:11

This is probably a dumb question, but how could the switch cause the bulb out sensor to go off?

lummert · Post by **lummert** » 21 Jun 2012, 00:48

Resistance in the light switch?

Post by **jimmy57** » 21 Jun 2012, 06:23

If you are going to hold me to it then I'm giving you an extra couple of choices: the connector to the headlight bulb has a bad connection and has partially melted from a bad connection causing resistance. Corriosion of the ground point for that lamp.

The bulb is the most likely. The other two are kind of a tie but are lesser in likelihood.

Bulb integrity sensor is next on the list.

Headlight switch is upstream so it would create no headlights but not a bulb out warning.

Pianoman702 · Post by **Pianoman702** » 21 Jun 2012, 08:55

Thanks for the replies (and I was only kidding about holding it to you Jimmy, haha). I guess I'll give it some time and if nothing happens, I'll try replacing both headlight bulbs to see what that does. Thanks for all the help. I'll update everyone when something new happens!

Zdadgeezer · Post by **Zdadgeezer** » 25 Jun 2012, 08:22

Was this spontaneous or after a bulb change? My experience has been to replace both sides/bulbs of the same type/location. I agree with the impedance mismatch theory in that case. Could also be caused by corrosion/ oxidation of the contacts, vaseline or other petroleum jelly on the bulb base is helpful in preserving clean contact surface. If both bulb replacement does not alleviate check your grounds.