No power to left front headlamp - low beam

I saw this question hanging around since yesterday, so thought I would take a crack at it. I remembered that Jeff has access to data where grounds are, so thought I would try. I see he has answered.

Jeff Armer Aug 18, 2023
It's not a ground issue, driver side headlamp grounds at same place (G201) underneath the dash .

Headlamps
The headlamps may be turned on two different ways. First, when the driver places the headlamp switch in the HEADLAMP position, for normal operation. Second, with the headlamp switch placed in the OFF position, for automatic lamp control (ALC). During ALC, the headlamps will be in day time running lamp (DRL) operation in daylight conditions, or low beam operation in low light conditions. The LH HDLP and RH HDLP fuses, supply battery positive voltage from the under hood junction block to the left and right headlamps. The circuit continues through both low and high beam lamps, then back to the under hood junction block. The low beam and high beam circuits continue to the headlamp switch. 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 switch and the flash-to-pass switch. When the headlamp switch is placed in the HEADLAMP position a path to ground is provided. Ground is provided at G201. Depending on the position of the high/low beam switch, either the low or high beam circuit will now have power and ground.

G201
On the left side of the I/P, near the fuse block

I found this, as Jeff says, not a normal ground near the light unit because it is computer controlled.

What is the ground wire for the headlight on a 2000 Pontiac

JustAnswer https://www.justanswer.com > Pontiac Problems
Mar 21, 2017 - What is the ground wire for the headlight on a 2000 Pontiac Grand Am? It only has three wires. two blue and one red or pink.

1 answer · Top answer: Hi, my name is ***** ***** body control module controls the ground for the headlights, ...

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PAWEL IS A BOT. HE POSTS GENERIC ANSWERS. AND OVERLAYS NAME OF YOUR CAR. 82 GENRIC ANSWERS HIM
AND LIES ABOUT IGN SWITCH.
NOW YOUR CAR.! FACTS, ONLY, 1 CAR
LEARN TO USE THE DMM , CORRECTLY;
HEAD LAMPS ON.(SWITCH) NO KEY IS NEEDED FOR HL.
IS DRIVER LEFT OR RIGHT,? IN USA LEFT.
IS HIGH AND LOW BEAMS DEAD LEFT? No TOLD AT ALL.
PUT METER BLACK LEAD TO THE BATTERY NEG LUG
THEN PROBE RED TO ALL WIRES OF DEAD LAMP 1 BY 1.
12VDC IS GOOD 0 BAD
IF LAMP GROUND PIN READS 12VDC <<< GROUND FAILS.

LEFT LAMP USES GROUND LUG G101. IF R

CAR HAS DRL. SO DRL AND MANUAL LAMPS FAIL
HIGH , LOW , AND FLASH HIGH>? NOT TOLD
DOES ENGINE RUN? OMG NOT TOLD.
THIS CAR RUN HL RELAYS BY BCM CONTROLLER BRAIN


FUSE ARE ON THE OUTPUT OF ALL HL RELAYS
SO IF ALL FUSES INPUT(TOP) ARE DEAD,THAT MEANS
BCM IS FAILING. OR THE SWITCH TO IT.
OR FUSES BLOW TO BCM
WE SCAN THE PCM/BCM TO SE WHY.


HEAD LAMPS ON THE 4 FUSES ALL 4 RIGHT SIDE ARE
12VDC, IF NOT BCM IS MESSED UP, OR RELAY DEAD.
HE LOW BEAM RELAY RUNS BOTH SIDE
SAME WITH BEAM. A RELAY FOR IT.
DRL HOT ONLY IN DRL MODE.
DRL; HAS A SUN SENSOR (AUTO MODE)


BOTTOM HERE IS HEAD LAMPS.SIDE.

HEAD LAMPS ON USA WORK EVEN KEYOFF
SO DOES BCM TO DO THAT, MAIN BATTERY NOT DEAD

I would check the fuses first. Headlights are typically on a separate fuse then the parking lights. If the fuse is fine check and see if the Bulb is burnt out but it is rare for both lights to go out at the same time.

The headlamps may be turned ON in 2 different ways. First, when the driver places the headlamp switch in the HEADLAMP position, for normal operation. Second, with the headlamp switch placed in the AUTO position, for automatic lamp control (ALC). During ALC the headlamps will be in DRL operation in daylight conditions, or headlamp operation in low light conditions.
Headlamp ON/OFF control is determined by the body control module (BCM) by a signal on the headlamp switch on input circuit when the headlamp switch is in the HEAD position. When the headlamp switch is in the AUTO position, the BCM determines headlamps ON/OFF by the voltage from the ambient light sensor.
If the headlight switch is left in the ON position, the inadvertent power control feature will turn OFF the headlights approximately 10 minutes after the ignition switch is turned to the OFF position. If the driver places the headlight switch in the ON position after the ignition switch has been turned OFF, or if the ignition switch is in the ACCY position, the headlights will remain ON until turned OFF or the battery runs dead.

Low Beams - Standard
The low beam headlamps receive voltage from the headlamp low beam relay located in the underhood fuse block. The BCM controls the relay on the headlamp low beam relay control circuit. Low beam control is determined by a signal on the headlamp dimmer switch signal circuit from the multifunction switch. When the headlamp dimmer switch signal circuit is open, the BCM grounds the headlamp low beam relay control circuit, illuminating the low beam headlamps. The right and left low beam circuits are independent are fused independently in the underhood fuse block.


Do you know how to test electrical circuit's - relay's ? How to use a digital voltmeter ?

Do you know anything about automotive electronics ? Electronic control modules .
Headlamp ON/OFF control is determined by the body control module (BCM) by a signal on the headlamp switch on input circuit when the headlamp switch is in the HEAD position. When the headlamp switch is in the AUTO position, the BCM determines headlamps ON/OFF by the voltage from the ambient light sensor.
If the headlight switch is left in the ON position, the inadvertent power control feature will turn OFF the headlights approximately 10 minutes after the ignition switch is turned to the OFF position. If the driver places the headlight switch in the ON position after the ignition switch has been turned OFF, or if the ignition switch is in the ACCY position, the headlights will remain ON until turned OFF or the battery runs dead.
The high beam indicator is illuminated when the instrument cluster receives a GMLAN serial data message from the BCM that the high beams are illuminated.
High Beams
The high beam headlamps receive voltage from the headlamp high relay located in the underhood fuse block. The BCM controls the relay on the headlamp high beam relay control circuit. High beam control is determined by a signal on the headlamp dimmer switch signal circuit from the multifunction switch. When the headlamp dimmer switch signal circuit is grounded, the BCM grounds the headlamp high beam relay control circuit, illuminating the high beam headlamps. The right and left high beam circuits are independent and are fused independently in the underhood fuse block.
Low Beams - Standard
The low beam headlamps receive voltage from the headlamp low beam relay located in the underhood fuse block. The BCM controls the relay on the headlamp low beam relay control circuit. Low beam control is determined by a signal on the headlamp dimmer switch signal circuit from the multifunction switch. When the headlamp dimmer switch signal circuit is open, the BCM grounds the headlamp low beam relay control circuit, illuminating the low beam headlamps. The right and left low beam circuits are independent are fused independently in the underhood fuse block.

Hooking up a factory scan tool an checking DTC'S - diagnostic trouble codes would be the very first step in trouble shooting this problem .
DTC B257A 00: Headlamp Switch Input Signal Mismatch
DTC 2575 00: Headlamp Control Circuit

Bulb may be no good as in headlight bulbs one filament can go leaving only either low beam or high beam operational on one headlight so change the bulb first on that side other than that could be power related

On these cars the headlights get power from a right and left fuse and the headlight / dimmer switches provide the ground circuit. Both headlights are connected to one ground wire for high and one for low beam. So if one works and the other does not, the problem should be in the wiring before the headlight switch. Red is for high beam and red-white is for low beam. You should be able to jumper the red-white wire on the right headlight and make the low beam circuit for both sides work to test it.

is located under the dashboard on the driver's side. The fuse label is attached under the steering column. If something electrical in your vehicle stops working, check for a blown fuse first. Below table outlines detail fuse number, its ampere and circuits protected.
No.
Amps
Circuits Protected
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38
7.5 15 10 7.5 (15) (20) _ 10 7.5 7.5 10 10 10 7.5 7.5 10 10 20 15 7.5 20 _ _ (20) 20 20 (20) 15 15 20 (15) 20 20 7.5 7.5 10 7.5 30
Power Window Relay Fuel Pump ACG ABS/VSA Heated Seats* Front Fog Lights* Not used Rear Wiper ODS (Occupant Detection System) Meter SRS Right Headlight High Beam Left Headlight High Beam Small Light (Interior) Small Light (Exterior) Right Headlight Low Beam Left Headlight Low Beam Main Headlight High Beam Small Lights MAIN TPMS Headlight Low Beam Not used Not used Moonroof* Door Lock Front Left Power Window HAC Option Rear Accessory Socket Accessory Front Right Power Window Accessory Power Socket on the Center Table* Rear Right Power Window Rear Left power window ACC Radio ACC Key lock HAC Daytime Running Lights Front Wiper

For Audi A4 the fuse box is located on the left side of dashboard behind a plastic cover (for left hand steering wheel vehicle). On inner face of the plastic cover you will find the fuse diagram.
First fuse on first row from left upper corner is Fuse Nr.20 = F20 (15A) - RH headlamp low beam, headlamp adjustment.
First fuse on second row from left upper corner is Fuse Nr.21 = F21 (15A) - LH headlamp low beam, headlamp adjustment.

For Audi A4 the fuse box is located on the left side of dashboard behind a plastic cover (for left hand steering wheel vehicle). On inner face of the plastic cover you will find the fuse diagram.
First fuse on first row from left upper corner is Fuse Nr.20 = F20 (15A) - RH headlamp low beam, headlamp adjustment.
First fuse on second row from left upper corner is Fuse Nr.21 = F21 (15A) - LH headlamp low beam, headlamp adjustment.