A few times recently, I start my 92 945t and get a warning light indicating a bulb is out. I get out of the car and check and they are all on. Where do I statrt with this? The problem is intermittent at this point.

Thanks.

Steve C

Here are the basics of how the Bulb Failure Sensor works...

The Sensor tests for an equal current on each side of these three pairs of lights (includes 3 bulb brake lights):

• Tail lights
• Brake lights
• Low headlight beams

With the car running, you can isolate the source of the BFS warning light to one of these groups as follows:
1 – Step on Brakes.... If no Warning light,
2 – Turn Parking (tail) lights on.... If still no Warning light,
3 – Turn on Low beams. Should be the cause of the Warning light.

If Warning light is ON when all these lights are OFF (or all test OK), it could be the BFSensor at fault But more often it is simply due to "mismatched" bulbs (different brands, age, or socket condition), or corrosion at the common ground points for Left & Right light housings ) that is causing the false warning light.

Note that there will be NO warning light if BOTH bulbs in a pair are out.
--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

Dear Steve C,

Good a.m. and may this find you well.


The problem could be:
(a) a loose wire or a weak/corroded ground wire
(b) corrosion on or in a bulb socket
(c) failing relay, which senses bulb failure
(d) if you've recently changed a single bulb, so the new bulb is not the same make/typc as its mate(s), that can trigger the bulb failure warning light.

From the intermittency, I'd start with (a) or (b).

Good luck tracking this down.

Yours faithfully,

spook

When ever I see the Bulb Failure come on, I assume everything is really OK. But when my lane changes trigger honking horn from the other drivers, I know it's time to check the bulbs.