How do i access the headlamp relay switch 2004 chevy impala

That year impala comes with a 3.4 l or 3.8 l vin K , no 3.6 . vin K

Headlamp relay is located in the left instrument panel fuse / relay box . Oper drivers door , pull plastic end from I/P . relay inside .

The headlamps are controlled by the BCM - body control module , do you know what that is ? The headlamp switch is a input to the BCM ,the BCM energizes relays to turn on the headlmps , low beam relay , high beam relay , DRL relay . These relay's are PCB - printed circuit board relay's ( non - serviceable ) If found to be bad the whole under hood fuse box would need to be replaced .
Low Beam Headlamp Operation
The low beam headlamps may be turned ON in 3 different ways:
• When the headlamp switch in the HEAD position for normal operations
• When the headlamp switch is in the AUTO position, for automatic lamp control (ALC)
• When the headlamp switch is placed in the AUTO position, with the windshield wipers ON in daylight conditions, after a 6 second delay
Battery voltage is applied at all times to the coil and switch sides of the LOW BEAM PCB Relay located in the underhood fuse block. When the headlamp switch is placed in the HEAD position, ground from G202 is applied through headlamps ON switch signal circuit to the body control module (BCM), signaling the headlamps ON request. In response to this signal, the BCM applies ground through the headlamp low beam relay control circuit energizing the low beam relay. With the relay energized, battery voltage is applied through the switch side of the relay, the left and right low beam fuses, and the low beam supply voltage circuits illuminating the low beam headlamps. Ground for the left headlamp is provided at G101 and the right headlamp at G100.

Do you know what B codes are ? BCM - DTC'S - diagnostic trouble codes , need a factory scanner or professional one to view these codes , not autozone or advance etc....Having a qualified repair shop check your vehicle would be your best bet.

DTC B2575 00: Headlamp Control Circuit

Circuit/System Description
The vehicle headlamps are controlled by the body control module (BCM) based on inputs from the headlamp switch and the turn signal/multifunction switch. The headlamp switch has four positions: Off, Auto, Park, and Headlamps. The default headlamp switch position is Auto, in which the BCM uses the ambient light sensor to determine when headlamps are needed. The Off portion of the headlamp switch is a momentary switch which overrides the automatic headlamps and will turn off the vehicle headlamps. When in the Off position, the headlamp switch grounds the headlamp switch headlamps off signal circuit, prompting the BCM to turn off the headlamps. The Park position of the headlamp switch will only illuminate the vehicle parking lamps. The Headlamp position of the headlamp switch will illuminate both the parking lamps, as well has the headlamps. With the headlamp switch in the Headlamp position, the headlamp switch headlamps on signal circuit is grounded, prompting the BCM to turn on the headlamps, regardless of other factors such as ambient light.
The headlamp high beams are controlled through the flash to pass switch and the headlamp dimmer switch, both located in the turn signal/multifunction switch. The flash to pass switch is a momentary type switch, designed to illuminate the high beams as long as the switch is held. With the switch closed, the flash to pass switch signal circuit is grounded, prompting the BCM to turn on the high beam lamps. The headlamp dimmer switch allows the operator to select between full time high or low beam operation. Unlike the flash to pass switch, it is not a momentary switch. When the headlamp dimmer switch is in the high beam position, the headlamp dimmer switch high beam signal circuit is grounded. This prompts the BCM to turn on the high beam lamps.
The BCM controls the headlamps based on the inputs explained above. When a low beam request is received, the BCM grounds the headlamp low beam relay control circuit. This energizes the coil in the LOW BEAM PCB relay, causing the relay switch to close. This then applies B+ to both low beam headlamps through the LT LO BEAM and RT LO BEAM fuses, illuminating the low beam headlamps. When a high beam request is received, the BCM grounds the headlamp high beam relay control circuit. This energizes the coil in the HIGH BEAM PCB relay, causing the relay switch to close. This then applies B+ to both high beam headlamps through the LT HI BEAM and RT HI BEAM fuses, illuminating the high beam headlamps

Headlamp relay is located in the left instrument panel fuse box . How To Replace Car Relay DIY Automotive Maintenance

Junction Block-Left I/P
Left side of the I/P, behind an access panel.
How To Test Relays EricTheCarGuy

High Beam Headlamp Operation
Battery voltage is applied at all times to the coil and switch sides of the HIGH BEAM PCB Relay located in the underhood fuse block. When the headlamp dimmer switch is placed in the high beam position, the headlamp dimmer switch signal circuit to the BCM is pulled low signaling the headlamp high beam request. In response to this signal, the BCM applies ground through the high beam relay control circuit energizing the high beam relay. With the high beam relay energized, battery voltage is applied through the switch side of the relay, the left and right high beam fuses, and the high beam supply voltage circuits illuminating the high beam headlamps. At the same time the BCM sends a GMLAN serial data message to the instrument panel cluster (IPC) requesting the IPC to illuminate the high beam indicator. Ground for the left headlamp is provided at G101 and the right headlamp at G100.

Check fan motor relay and temp. switch in block.

change your signal light switch. i just had the same problem. cost me a 150.00 for an after market switch, comes with a full harness that plugs in under the dash.

under the hood in the fuse/relay box there will be a relay for the automatic headlamps, also a relay marked drl daytime runnin lamp, sometimes there one and the same.

if you have auto lights it could be the photo eye or its the headlight switch

It sounds like your low headlight relay may not be working. not sure on this particular model, but most of them have relays for high and low beam headlamps. these are usually located in the power distribution panel under the hood. before replacing make sure you have power to them. if not check for wiring problem, if power is present try a different relay.

Ok, locate the relay panel (probably inder the hood) and find the relay that controls the headlamps. With your headlight switch "on", pull the relay and see if your getting a hot current to the connectors in the relay panel. If it's hot, replace the relay. If no current, it's probably your headlight switch.