Question about 2004 Chevrolet TrailBlazer

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Head light / fan clutch relay swap service engine light.

Hello, I have a 2004 trailblazer. Recently the low beams stopped working. I swapped the relay with the fan clutch relay. wala! they work. I switched them back planning on buying a new relay. Well my boyfriend decides to swap them back so he can drive my car at night! Then tells me he intentionally drove around and let it sit in idle to see if it would over heat! WHAT???
Well anyway I get back from work and now my service engine light is on, even after swapping the relays back again. I plan on getting to autozone today for a new relay. But in the mean time can you tell me how to go about this?

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You have to reset the computer, do this by removing the positive cable for 10 mins.

Posted on Nov 26, 2008

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1 Answer

Why doesn't my low beam headlights work when all the other lights do ?


The most common cause of low beam failure on trailblazer, buick, and GMC, are the micro relay under hood in fuse box. One relay is for the low beams and the other one (beside it) is for the cooling fan. It is part number 15016745 and has four prongs on it. Just swap the cooling fan relay, with the low beam relay. This will tell you if it is bad. Then see if low beams work, If they do its a bad relay. Good-Day! Make sure to swap the relays back so that the cooling fan is working ok!

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Lowbeam headlights wont work, brake lights are out and check engine light is on...changed th dimmer switch, no luck


For the low beam problem, Swap relays 45 & 46 in the underhood fuse panel. Relay 46 is for the Low Beams. If that fixes the light, replace the relay that cam out of position 46.
Since the high mounted brake light is working, that indicates that the brake switch is good. You need to check the bulbs in the rear tail light assembly, if they are good, check fuse #34.

Sep 01, 2012 | 2004 Chevrolet TrailBlazer

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Low beam head lights won't work fuses are ok


What fuse did you check? There is a relay that controls the low beams, it is #46 in the underhood fuse panel. Try swapping it with #45.

Feb 20, 2011 | 2004 Chevrolet TrailBlazer

1 Answer

2004 chevy trailblazer, Both low beam headlamps are out. Headlamps replaced(same problem). Fuses are good. High beams work fine.


There should be a relay for the low beams. Locate and replace, Or swap it with another relay to see if that fixes the problem.

Dec 27, 2010 | 2004 Chevrolet TrailBlazer

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Both of my low beams just stopped working at once. High beams work fine, and bulbs seem to be good. We've replaced the fuses also, and it hasn't worked. what would cause the low beams to both just quit...


The headlight relay has probably failed. This relay is in the underhood fuse box. There are typically two of the same relays in there, so you can swap the low-beam relay for the high-beam relay to verify the problem before you shell out $30 for new relay.

Oct 21, 2010 | 2004 Chevrolet TrailBlazer

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The Saturday before Easter I was doing last minute shopping,when i got in the car to leave my headlight wouldn't work.The parking lights and high beams work, I changed the bulbs that didn't work. I got in...


Try temporarily swapping #45 Cooling Fan relay and and #46 HDM relay in the under-hood fuse block, and see if the low beams come on.

The one originally in the HDM #46 socket is bad. That relay is actually is a solid state module, not a conventional relay, and will cost you anywhere from $25-45 at the dealer.

HDM = Headlight Driver Module

Also known as a solid-state relay, since instead of relay contacts and a coil, it uses a power switching transistor capable of running the headlights (and the fan clutch in #45) at less than 100% power, to provide daytime running lights, and control the fan clutch engagement for the engine cooling fan.

Thank you for using fixya and be safe.

Apr 16, 2010 | 2006 Chevrolet Trailblazer

1 Answer

Highbeams work but low beams wil come on regardless of the settings. Chcked fuses and they are fine.


Check the relay #15016745 in the under hood fuse box. It is in position 46. There are actually two of them side by side, one for the low beams and one for the cooling fan. Swap the two relays and see if the headlights work, if so you have found the problem. Swap them back and purchase a replacement relay. The dealer should have them for around $45, other parts stores may have them or you may find them on ebay by searching for 15016745.

Feb 28, 2010 | 2004 Chevrolet TrailBlazer

3 Answers

2002 chevy trailblazer low beam lights will not come on.


if both lamps dont work a common problem was the headlamp module. It looks like a black relay in the underhood fuse block (next to the master cylinder), there is two black small relays right next to each other (they used to say 15016745 on top in white letters.) One is for the low beams and one is for the fan clutch. Swap them and check the lamps - if the come on, go get a new one at the dealer and replace the bad one. If you leave the bad one in the fan clutch your gas mileage will be bad and your ses light will come on.

Mar 31, 2009 | 2002 Chevrolet TrailBlazer

1 Answer

Low beams will not turn on - checked fuses,solenoids,bulbs and changed the light switch- low beam lights went off then three days later came back on . now they are out again.


Check the relay module. 45 or 46. on the engine relay block. you can swap the two they are the same part number, then you will know. Dont start the engine, just check the lights. If it works replace the relay module. You may have to order the part from the parts store. Or go to the dealer to get it.

Mar 20, 2009 | 2004 Chevrolet TrailBlazer

3 Answers

Front lights do not turn on.


This is, in fact, correct. The problem you're describing I just repaired. The problem is a relay in the fuse panel. There are two identical black relays, one for the headlights on/off function and the other is for the fan clutch. Please do not just swap one for the other, if your headlights are not switching off and swapping these relays appears to solve your problem, this would indicate that the initial relay is faulty and needs to be replaced. Operating your vehicle with a blown relay in the fan clutch's fuse panel will result in your vehicle eventually overheating. The part cost me about $40 from my nearest Chevy dealer and was easy enough for any novice to replace on their own.

Jan 14, 2009 | 2004 Chevrolet TrailBlazer

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