Headlights not working - low beams?

The headlights are controlled by the BCM which is sounds like it is going out but to be sure lets do a CAN scan which is the future of automotive repair you can get a CAN scanner from Amazon for about $50.00 here is a video to show you how.

https://youtu.be/InIlnsjOVFA

Also here is a guide to help check the wiring with the headlight wiring diagrams below so you can see how the system works.

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

Also let me know all the exact code numbers you have not code descriptions. Check out the diagrams (Below). Let us know what happens and please upload pictures or videos of the problem.

I have a multi-meter. I also have a Actron AutoScanner. Although it is not a professional model, it is a scanner and code reader. I will scan/read the vehicle today to see if any codes are listed. There are no indicators that have illuminated on the dash.
Thanks for the response.

Your scanner will only read engine codes and some of the transmission codes.You need a scan tool that can reqd the body control and all the other computer's in your vechile.Unfornately the newer the vechile the more computers you have. They have codes for everything on the newer cars turn signals etc.That's why I say get a professional scan tool to scan all the computers in your car.Also sometimes it takes those scan tools to diagnose the problem even.Make sure you get the exact code numbers.Makes it more difficult to diagnose also.

My unit is a Actron CP9145. It did not show any issues.

By a professional scan, am I able to get this done at a auto parts store or do I have to go to a mechanic/dealer?

Your scan tool can only read engine and transmissioncodes also the same with the auto parts store.A ddealer or shop would have the real expensive scan tool that can read all the different computers codes.Let's start with the multi meter and see share it leads.Let's start by turning on the low beams and see what were missing at the low beam bulb connector power or ground?

Another bit of strange information for you. I was told by a neighbor to take out the relay and put it back in regarding a possible contact issue. In the engine compartment, I removed the cover from the fuse/relay box. The schematic on the underside of the cover stated the relay for the low beam lights & wipers should be in position #37; however, there was no relay in that slot. The windshield wipers work fine. Does this make any sense to you?

As soon as I can do the diagnostics on the low beams I will get back to you. We're supposed to get a lot of rain shortly, so I do not know when I can start.

Thank you.

Relay number 46 labeled HDM RELAY also fuse number 6 and fuse number 3 feeds power to the low beam bulbs. This is all in the under hood fuse box.

Also fuse number 57 feeds power to the the bcm relay.

Thank you for the additional information. What does "bcm" stand for?

Update: In order to access the bulbs and connections, by removing the headlight housing, the grill has to be removed. I was able to remove all this and put the headlight housings back on the vehicle before dark. I did not have any time to do testing. When I did a head light check, now the high beams do not work either except in the flash mode. They did work prior to the removal and re installation of the headlight housings. Does this give you any additional clues?

Sorry about the bcm that was a mistake I ment to say hdm relay feed for the number 57 fuse.Also what don't you have to the bulbs power or ground?You may have a loose connection if the high beams don't work now that you moved the wires around.

Replaced relay # 46 HDM.

Problem solved.

glad to hear you got it fixed that's what we like to.hear

My low beams are intermittently working. I have replaced the HDM relays and every applicable fuse related to the low beams. Nothing has resolved the issue. I am unsure if they is a ground issue or something else. If anyone has had to go past the fuse and relay solution, please let me know.

Thank you,

Tyler

Hi,

It won't be a ground issue because the low and high beam have a common ground. Since the high works, the low should too.

I attached a pic below of the headlamp schematic. Check all of the fuses I indicated as well as relay 46.

Here are a few links you may find helpful:

https://www.2carpros.com/articles/how-to-check-a-car-fuse

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

https://www.2carpros.com/articles/how-to-check-wiring

Let me know what you find.
'
Joe

All of the fuses and relays are good. I am stumped.

Have you checked if there is power to the socket?

Yes, do you think the headlight control in the dash or the dimmer/cruise control switch could be an issue?

Do you mean there is power to the light socket? If not, there is one other thing I need you to check. The lamps are grounded at the same point. However, when looking at the wiring schematic, I'm questioning the HDM relay ground. Take a look at the schematic below and if possible, check the ground for the relay and the splice.

Let me know what you find.

Joe

hello i have a 07 chevy trailblazer with the 4.2L inline six 4wd. I have a problem with the low beam (Both Low Beams) going off at the same time and stay off for 2 secs or longer

check item in pic for a bad relay or corrosion on it use dielectric compound on the prongs. if not that then have it scanned for a body module problem. Check out the diagrams (Below). Please let us know if you need anything else to get the problem fixed.

I have a 2006 Chevy Trailblazer and last night both headlights went out at the same time. The bulbs are brand new so that shouldn't be the problem. I checked the fuses and can't see a problem with them. Also switched relay #45 with #46 and nothing happened so that doesn't appear to be the problem either. PLEASE HELP

Did you check for voltage anywhere? Did you check for voltage at the fuse circuit? Neither high or low beam will work? Our database info says bcm controls ground side of headlamp relays, so check for applicable trouble codes. There are headlamp control codes. I believe those are B type codes. Some of the national brand autostores will check codes for free. Let us know.

changed out the light relay and it didn't work. if you move relay back and forth the headlights go on and off. I think the female plug in that the relay fits in are worn out. what can I do to fix this problem?

You are probably correct that the terminal is the issue. You will need to either de-pin the connector and tighten the terminal or you will need to replace the connector if it is loose and allowing the terminal to move around.

We don't have any videos on how to tighten a terminal but there are a ton of DIY videos on the internet that will give you the idea on what needs to be done.

The other solution is to replace the fuse box. I attached the instructions below on how to do this for the fuse box with the park relay. Let me know what questions you have.

06 trailblazer low beam headlights went out at same time tried another bulb no luck high beam are fine

Have you checked to see if you have power to both sides of the low beam fuse?

i have a 2004 the problem is in the fuse box under the hood it is called an hdm relay its a square black one autozone has them for 35 bucks.

the headlights go from the headlight switch to the dimmer switch then to the bulbs.the switch is on the l/side lower steering column when u dim the lights u will see the linkage rod will move as you move the dimmer lever.check the voltage their.

After having a buddy do collision repair on driver side fender and headlight low beam and turn signal don't work on driver side only. high beams are okay. my question is, if it's not the bulb or fuse what could it be?

Hi,

If the fuse in pic 1 is good, then I suspect it is a ground issue. If you look at pics 2 and 3, you will see "S107" and then "G107". The S means there are several wires spliced together. Since the high beam still works, the the ground (G107) is likely still good and the ground wire to the high beam is still attached. However, both the low beam and the signal light for the driver's side splice together with the same ground. I suspect that is where the problem is located.

Here is a simple test I need you to do: Note that the ground wire for both lights is black in color. Simply run a jumper wire from the black wire to the battery ground and see if the light works. If it does, then we know the splice is likely the issue. You don't have to run it all the way to the battery, but you need to provide a known good ground location on the vehicle to confirm.

Let me know if you have other questions and what you find.

Take care,
Joe