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I have a '04 Envoy that both driver and passenger sides headlights are out. It's not the bulbs, i replaced both of them. i checked the fuse and the fuse is fine, so i tested the wiring of the connector of the headlamp, and on both sides passenger and driver, i'm getting a short with all of the wires. theres 2 sets on the connector. the hi beams and the low beams and they're all shorted. what else can i check to fix my problem.

-manny
 

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2007 chevy trailblazer_ss_1ss
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If the wires are shorted the fuse would be blown. Does the light on the dash come on when the switch is flipped? Is it just the lowbeams or are ALL the lighbulbs in the headlight out? What about the rear bulbs?
 

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2002 chevy trailblazer_ls
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Try temporarily swapping #45 Cooling Fan relay and and #46 HDM relay in the underhood fuse block, and see if the low beams come on.
 

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Discussion Starter #7
I swapped both relays 45 and 46 and they came on. Now what does this mean which one of my relays is bad or is it a bad relay.
 

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2007 chevy trailblazer_ss_1ss
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I swapped both relays 45 and 46 and they came on. Now what does this mean which one of my relays is bad or is it a bad relay.
If you tried a different relay in there, and the lights work fine now then the relay is bad. Less than $10 at the dealer (I can't remember how much it is off hand).
 

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2002 chevy trailblazer_ls
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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.
 

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2003 chevy trailblazer_lt
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Thanks.

I know this is an old thread, but thanks. I tried everything I could think of. Not a mechanic by trade BUT an electrical engineer. Then I search for 'low beam' and read about HDM relay. Right there. Now if I only knew what HDM was, I might have figured it out on my own.

Darin
BadFishRacing
 

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Now if I only knew what HDM was,
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.
 

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Thanks

after fighting this crap all day, i find this thread and low and behold. THE PROBLEM IS SOLVED. thanks for not deleting this thread!

(BIG SIGH OF RELIEF)

:thumbsup:
 

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this post saved me, thank you.

I have a question, since I have a mechanical fan, not an electric cooling fan, can I just use the cooling fan relay permanently? Or does that control something else as well?
 

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2002 chevy trailblazer_ls
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this post saved me, thank you.

I have a question, since I have a mechanical fan, not an electric cooling fan, can I just use the cooling fan relay permanently? Or does that control something else as well?

You have the engine cooling fan with the electroviscous (EV) clutch which the amount of engagement is controlled by the PCM through that cooling fan relay. That relay is a solid-state module that can contol a range from 0 to 100% on. If that's gone you lose electrical control of the fan clutch and set a DTC.
 

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2002 gmc envoy_sle
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Currently having the same problem and came to the same conclusion...
switched the 45 for 46 and away we go HOWEVER... the next day the check engine lite comes on and the sob's want $69.85 canadian for the HDM in canada.
No wonder they are going bankrupt.
im currently looking on e bay or aftermarket but so far no luck. anyone here find an aftermarket supplier for HDM yet?
 

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2002 chevy trailblazer_ls
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Currently having the same problem and came to the same conclusion...
switched the 45 for 46 and away we go HOWEVER... the next day the check engine lite comes on and the sob's want $69.85 canadian for the HDM in canada.
No wonder they are going bankrupt.
im currently looking on e bay or aftermarket but so far no luck. anyone here find an aftermarket supplier for HDM yet?
Hey at least you didn't have to pay to have it diagnosed! Last time I checked dealer cost on that was about $25. If GM was getting $70 for a HDM maybe they wouldn't be broke! But.. every TB will have two in the fuse block, so you'd think salvage yards should have a few. (Seems I read the 2008s don't have the electro-viscous clutch any more- GM to a mechanical thermal bi-metal type, so the '08s might just have one module like that).
 

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2002 chevy trailblazer_lt
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headlight low beam problem

I too have no low beams or DRL's. 2002 TrailBlazer. Fuses #3 and #6 good. Switched #45 and #46. Still no low beams. All other lights work including dash, high beams and light for selector switch. Pulled #3 fuse, turned on headlights and do not have power where the fuse plugs in. Got any other ideas before I go to dealer?:cry:
 

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I too have no low beams or DRL's. 2002 TrailBlazer. Fuses #3 and #6 good. Switched #45 and #46. Still no low beams. All other lights work including dash, high beams and light for selector switch. Pulled #3 fuse, turned on headlights and do not have power where the fuse plugs in. Got any other ideas before I go to dealer?:cry:
Pull HDM #46 and look at socket connector pin #2 there should be battery voltage there. You may have to check each one they aren't numbered only one will have the battery voltage on it. Others are the output to the low beams, the control from the BCM and ground.
 

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Pull HDM #46 and look at socket connector pin #2 there should be battery voltage there. You may have to check each one they aren't numbered only one will have the battery voltage on it. Others are the output to the low beams, the control from the BCM and ground.
OK With the light selector on or off I have power to the socket connector (HDM # 46) thats by itself. As you said only one had power. What's this mean? #45 and #46 both bad? :confused:
 
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