2005 buick lesabre low beams not working at night daytime running lights work hi beams work dimmer switch works relays and fuses are good. what do I check now and how?

If the main beams work, it is unlikely to be a grounds issue, but you could check with a meter from the connector to the vehicle body.

The most likely reasons would be the bulb, the fuse, the relay, or the headlight switch itself.

Hi Ricky, Im AL the owner of Big As Auto Repair.

Ricky, if the high beams work when you hold the lever in, then its the high beam switch NOT the light switch. The lever controls the high and low beams. You need the multi-function switch which is also the dimmer switch. Hope this helps and please visit my auto-repair-website at: http://www.bigasautorepair.com/

Headlamps Inoperative - Low Beams

Step

Action

Value(s)

Yes

No

DEFINITION: This diagnostic procedure should only be used if the high beam headlamps are operating properly and the low beams are inoperative.

1

Did you perform the Headlights System Check?
--
Go to Step 2
Go to Headlight System Check

2

1. Turn the headlamp and panel dimmer switch to the ON position.
2. Move the headlamp dimmer switch to the LOW position.
3. Backprobe the headlamp dimmer switch connector with a J 35616-200 from cavity A to ground.

Does the test lamp light?
--
Go to Step 3
Go to Step 5

3

1. Remove the daytime running lamp relay.
2. Connect a J 35616-200 at cavity G5 to ground.

Does the test lamp light?
--
Go to Step 4
Go to Step 6

4

1. Re-install the daytime running lamp relay.
2. Backprobe cavity B at the high/low beam headlamp with the headlamp dimmer switch in the LOW position.

Does the test lamp light?
--
Go to Step 7
Go to Step 8

5

Replace the headlamp dimmer switch.

Is the repair complete?
--
Go to Headlight System Check
--

6

Repair the open in CKT 359 (PPL) between the headlamp dimmer switch and the daytime running lamp relay.

Is the repair complete?
--
Go to Headlight System Check
--

7

Replace the high/low beam headlamps.

Is the repair complete?
--
Go to Headlight System Check
--

8

1. Inspect for an open in CKT 12 (TAN) between the daytime running lamp relay and S120, repair as necessary.
2. Replace the daytime running lamp relay if no open was found in CKT 12 (TAN) between the daytime running lamp relay and S120.

Is the repair complete?
--
Go to Headlight System Check
--

If your lows do not work at all before you do anything make sure your both low beam bulbs are not blown out. My freinds car had this happen and he replaced both bulbs and they work now. Next check the fuses. There is a tester you can buy that has needle tips so you can poke the wires and see if you have power getting in the wires. You poke the black into the ground wire and red in the power side..
There are also head light relays you might want to check also.

The headlight relay provides power to the dimmer relay, then power goes thru a fuse for each light for each circuit (4). The low beam fuses are in fuse block 2. The dimmer relay is controlled by the daytime running light module. The headlight and dimmer switches send signals to the DRL module. You may need a shop manual to troubleshoot the circuits.

The high and low beam lights use the same power source, so if the low beams work the high beams have power.
There is a low and high beam relay controlled by the dimmer switch.
If the low beams work and the high beams don't, and the bulbs are good, check the dimmer switch and the high beam relay.

Headlamps
The headlamps are operated when the driver places the headlamp switch in the HEADLAMP position. The LT HDLP and RT HDLP fuse in the IP fuse block, supply battery positive voltage to both the left and right headlamps. The low beam and high beam circuits continue to the headlamp switch. Depending on the position of the dimmer switch, either the low or high beam circuit will now have a path to ground. Ground is provided at G204. The low beam and high beam circuits also provide the body control module (BCM) with both low and high beam inputs. The headlamp switch includes the dimmer and the flash-to-pass switch.
If the headlight switch is left in the HEADLAMP position, the headlights will remain on until turned off or the battery runs dead.
Daytime Running Lamps (DRL)
Any function that turns on the headlights will cancel the daytime running lamps operation. The LT HDLP fuse in the IP fuse block supplies battery positive voltage to the daytime running lamp (DRL) relay coil circuit. The DRL relay switch contacts are connected to the low beam circuit. When the headlamp switch is placed in the OFF position, the BCM will turn on the daytime running lamps. The BCM energizes the DRL relay, closing the switch contacts and grounding the low beam circuit at G204. The DRL illuminate the low beam headlights at a reduced intensity. The DRL will operate when the ignition switch is in the RUN position, the gear selector is not in the PARK position and the parking brake is released. When these conditions have been met the DRL will illuminate.
DRL operation in Manual Transmission equipped vehicles will occur when the ignition switch is in the RUN position, and the parking brake is released.

Probably the dimmer switch . But without testing that would be just a guess . Turnning the headlamps on Any function that turns on the headlights will cancel the daytime running lamps operation..
No ,don't think the DRL relay has anything to do with it .

View wiring diagrams an testing the electrical circuits at the dimmer switch would be the proper way to diagnose .

Check out your fuse associate with the low beam headlight, secondly there is a relay fuse under fuse rely box under the hoos. Locate this box, and locate the relay fuse associated to the low beam. You can rotate the relay with another relay of the same spec to see if the low beam lights are coming on. I would believe that it is a fuse that is blown, check your owners manaual on the location of the fuse box. Usually it's located in the driver side kick panel.

The most likely cause is a bad multi-function switch which for ease of understanding is the turn signal switch which is also the dimmer switch. there is a procedure for checking this but if you are not skilled at reading a wiring diagram I don't recomend it.

If the low beam head light relay is fine,and the dimmer switch checks out fine,then look at the out put wire from the dimmer switch to the head light relay,check for voltage,then check the relay to see if it energizes.Then follow the wire(out put)from the relay to the head light.Now if power from the dimmer is getting to the relay,but the relay is not energizing,look for a bad relay,or bad relay ground wire.