This 2004 Chevrolet Trailblazer came in with the complaint that neither one of the low beam headlights would work. They both stopped working at the same time. The customer had already paid another shop to have the headlight and dimmer switches replaced. After several days of trying hit and miss diagnosis she called me. I told her that I should be able to have her vehicle in and out of the shop in less than fifteen minutes and the bill would be around $65.
The first step in this easy repair is to locate the underhood fuse box assembly, located under the hood on the driver’s side of the vehicle.
After removing the outer cover, you should find an inner cover that also will have to be removed.
On the inside of the main fuse box cover there should be a fuse box legend. On the far right hand side of the legend is a listing for solid state relays. The relay we are looking for is designated as an HDM relay. It is identified as being relay number 46.
Looking at the legend for part number 46, we find that it is located nearly in the center of the fuse box but slightly towards the fender.
Here is the actual relay in the fuse box. The first thing that I noticed was that the relay had a different physical appearance compared to a factory relay. It should have been black, shiny and had the part number stamped on top. The part number is 15016745. It should have looked just like the relay located next to it that is designated as relay number 45. This relay had already been replaced with an aftermarket relay once and it had failed again. I strongly recommend using the original equipment relay if possible. They just last longer. To purchase the relay, click here.
It takes a firm grip to grasp the relay and pull it from the fuse box. A pair of pliers can be used, just make sure you don’t grab it too tightly and crush it.
Now the simplest was to test the relay is that if you know relay 45 is good, remove it. Also note that there are numbers next to the terminals on the underside of the relay.
Terminal #1 is not used.
Terminal #2 should have battery power on it at all times.
Terminal #3 is not used.
Terminal #4 is the relay output terminal to the low beam headlight fuses #3 & #6.
Terminal #5 is switch battery power from the BCM. I do not recommend testing this terminal with a test light.
Terminal #6 is continuous battery ground and is terminated at the lower left side of the engine.
In doing testing, take your time and do not allow yourself to be fooled by mirror images. I always place my finger on the relay terminal that I want to test and then rotate the relay into position to identify the corresponding terminal in the fuse box.
Then install it into the relay 46 position. If the headlights work, you know that you will need to purchase a new relay. I know the temptation is there to just swap relays but keep in mind that relay 45 is for the engine fan clutch. You may wind up with an overheating condition if you do.
The new relay has been installed for the low beam headlights and the original relay for the fan was restored to it’s location. I personally recommend changing both relays while you are there but I will leave that up to you. If you would like a deal on buying both relays, click here.
The headlights now work again and all I have to do is install the rubber cover over the low beam opening in the rear of the headlight assembly. The last shop left it off and the customer asked if I would install it.
The last word on this repair is that if you remember the relay had already been replaced with an aftermarket relay once and it had failed again. I strongly recommend using the original equipment relay if possible.