volvo s60 2005 mystery lob beam Voltage dropping

adrian22 · Post by **adrian22** » 16 Aug 2016, 14:00

I got the "Low beam bulb failure "I have changed the light bulb on the driver side but lights don't work. Bulb is new and good-checked with another battery. The passenger side light is working ok. I know left and right have separate circuits. Checked both RH and LH fuses, they are ok .Measured voltage at the fuse connector. On the working passenger side Voltage consistent 12V but on the driver side when I connect voltmeter the fuse I have 12v for 1 second then Voltage dropping from 12 v to 0 v in one second and stay to 0. That is very strange? I was expecting 12v or 0, but dropping voltage is inexplicable-At the bulb connector there is no power( bulb to ground 0)
Question
There is any relay or capacitor that is responsible for each low beam bulbs? That will explain Voltage dropping on one side only

Post by **mrbrian200** » 05 Sep 2016, 02:37

The Low beam fuses are before the CEM and feeds from the main +B wire, so you're looking at one of the terminals/wires right there within the underhood junction box losing continuity when current is run through it (heat).
To know for sure jump between the +B (where you would attach positive jumper cable) to the battery side of the fuse (not the lamp side) which is merely bypassing that bit of wiring. That fuse would normally be hot at all times. The light is switched on/off down the line by a relay inside the CEM.

The low beam circuits run from the junction box in engine compartment (fuse) -> CEM -> back out to the lamps so that the CEM can sense a failure. Puzzlingly the high beams +B doesn't come from the underhood junction box, but instead through separate +B wires that run directly between the trunk to the CEM.

adrian22 · Post by **adrian22** » 05 Sep 2016, 08:18

thanks so much for your kind reply
I did jump the defective lamp fuse socket with a wire from the working lamp fuse hopping to bypass the CEM relay but still not able to fix it. I suspect the defective lamp relay control is burned out and I dont want replace CEM
If I understand correctly your solution is to and supply power directly from the battery to the defective fuse?
I will try that but I dont see how to solve the defective relay problem
Question is can I use the working relay to switch on/off both lamps?

adrian22 · Post by **adrian22** » 05 Sep 2016, 08:21

or I can permanently jump a wire from the working light to the defective light?