2004 GMC Envoy Logo
Posted on Nov 28, 2010
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Is there more than one relay switch? I found one for the high beams but not one for the low beams. I changed my dimmer switch and the bulbs but nothing has helped, I have high beams just not low beams and I have no power going to my fuses for right or left low beams

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Freddy

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  • GMC Master 1,311 Answers
  • Posted on Nov 29, 2010
Freddy
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The low beam relay is #46 in the underhood fuse panel. check its contact pins before replacing it. If they are corroded, try cleaning them first.

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3answers

I have a 2005 chevy trailblazer and the low beam lights randomly work. I have to drive with my high beams on. we have changed the bulbs, the relay. sometimes the low beams come on in the morning

if this unit has a multifunction(turn signal switch with head lights) switch its about 99% the problem. for sure it is the dimmer switch wherever it is located.
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Low beam headlights do not work 2010 chevy impala high beams work as do daytime running lights low beams do not work on either automatic mode or manual mode

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
1helpful
1answer

I have a 00 ford explorer I have low beam no high beam I replace the bulbs and the dimmer switch I still don't have high beam why?

Normally, a relay switches the lamps between high and low beams; the dimmer switch controls the relay.
Check relay/fuse center covers for a legend describing the functions of the relays present.
Empty positions are normal and provided for accessories.

Many of the relays will bear the same part number so if you can locate the layout legend and find the headlight relay, exchange it with another of the same type to check the suspected one for function.
0helpful
2answers

High beam not working

id just replace the bulb, socket,and your sure you checked all fuses
0helpful
1answer

No headlights working

Just low beams headlamp switch, bulbs, dimmer switch, low beam relay, fuses
just hi beams : dimmer switch, high beam relay, bulbs , fuse
Both Headlamp switch , dimmer switch, fuse, bulbs.
1helpful
1answer

Is there any fuses or relays that are not in the fuse box on a 2002 buick rendezvousfor the bright lights

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.
0helpful
1answer

Low beams not working, but high are..

Year and model ?
Can you turn the headlights on and get the high beams, then nothing on low ? Or just get high beams when you pull on the dimmer switch ?
0helpful
1answer

I have a 1993 Honda Accord and the head lights won't turn on. I have changed the fuze and added new bulbs. what else can it be.

do you have low or high beams?

LOW BEAMS: When headlight switch is turned on the headlight relay is energized providing voltage through fuse 37 and 38 to the headlights and the low beams come on.

HIGH BEAMS : same thing as above thru fuses 37 & 38. When the dimmer is in high, the dimmer relay provides ground to the high beams, and the high beams come on.

1. pull your flash see if lights come on?
2. check fuse 15 if good
3. check fuses 37 & 38.
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