Low beams not working - 2003 Subaru Legacy Outback - MT

[Hbondar]

Hi all - I live in California and am helping my son who is in Colorado to diagnose his lighting issue.  As I do not have the car nearby and only worked on the car once,  while replacing the infamous head gaskets,  I am admittedly a little under informed.  But here goes - and appreciative in advance for any help:

 

Situation:  Both low beams and Daytime running lights(which he tells me are the side marker lights??) are not operating.  Hi beams work.  Bulbs passed continuity check,  Relay has been swapped and indicates normal operation.  He disconnected the DLR and this did not allow the low beams to operate.

 

I have done some research and it suggests the following - but I am not sure.  Here are my conclusions - point x point.  Please correct me if wrong:

 

1. Body control unit - has no relation to headlight operation.

 

2. Illumination unit - has no relation to headlight operation

 

3.  DLR - would have thought this was the culprit but when disconnected it did not resolve the problem. ( I should note that he to thought the bulbs were the problem and replaced them with LED bulbs - I point this out just in case this clouds the result of the DLR relay disconnection test.

 

4. Connector near firewall - I read somewhere that someone had a problem with this; cleaned it and it fixed the problem.  He has not located this yet.

 

 

 

Any thoughts on the conclusions made and what steps he can take to diagnose the issue.  Many thanks - Harvey

[Fairtax4me]

Daytime running lights use a filament in the headlamp bulb. Typically the high beam filament, but at a reduced voltage. Not sure of which filament your year subaru uses.

 

Fuses. Have they all been checked? You can check relays all you want, but fuses are where the power comes from.

 

Another somewhat common issue with those years is a bad headlamp dimmer switch on the steering column.

[Hbondar]

thanks - fuses have all been checked.  What is the diagnostic for the dimmer switch.  Is that active when the lows are on?

[Hbondar]

also - my understanding is that the witch has separate circuits and contacts for Left vs. Right making it less likely this is the cause of a dual failure. ????

[Numbchux]

High and Low beam use the same fuses/relays

 

Low beam and Daytime Running Lights both use the same filament in the bulbs.

 

I'd test for power across the bulb connector, if it passes, try a new bulb. If it fails, then isolate whether it's the power or ground side of the circuit that has failed (test each wire individually, referencing straight to the battery for the other). The power side has the same source as the high beams, so I assume that will be fine.

 

I just spent quite some time studying the diagrams for that circuit (btw, the 2003 diagram has 2 wires for the Daytime Running Light relay switched, and it didn't make sense, but I had the same diagram printed for my '04, and it does make sense). I don't see a common component that could cause both issues other than the bulb itself (I have seen bulbs have some continuity, but not light up...). The Daytime Running Light module and relay would both have to be failed, I think. And they get their power from the same fuse that supplies power to the ECU and fuel pump (so if it runs, we can assume that is fine).