What would cause low beam headlights not work when all other lights work including high beams and fuses are all good on a 2005 Chevy trailblazer?

Answer 1

If the bulbs have been replaced with new ones and they still don't work then check the harness that connects to the bulbs. They have failed in the past.

OR

It's probably the Headlamp Relay. Its GM part number #15016745. Its a bit hard to find at most parts houses but most GM parts shops have them. Look to pay around $26 if you can order online, $32-42 if you want to pick it up locally. The high end is from the dealers themselves.

Easiest way to check is swap the Headlamp Relay (also called the Driver Control Module Relay if I remember correctly) with the cooling system relay, they are the exact same part. Do this with the car turned off, make the swap and check your low beams. Its a fairly common problem with the Chevy Trailblazer/GMC Envoy/Buick Rainier series.

There are two such relays in the under hood fuse box. One controls the low beams and one controls a cooling fan. They both have 15016745 part number on them and the low beam relay is in position 46. Swap the two relays and see if your low beams work. If so you have found your problem. Swap the relays back and get a replacement relay. I found mine on eBay for $20.

At Napa Online it said the part number was ECH AR6100 and in my area costs $50

At Oreilly Auto it is part # R6100 (ask them for the blower motor relay)

You want the pin-out to be 1 and 3 not the 2 and 2, helpful if you take the relay in to them. In the relay box in the engine compartment (driver side), you can take off the top lid and under it you will see a layout of the fuses and what goes to what and where. You may need a pair of plier to help pull it out