no low beam but drls work

2003 tacoma v6 auto 4x4 drls

Ok I think I have a fairly unique situation and im going to try to explain it best I can because everyone I've asked has had a hard time following my thought process

My headlight low beams don't work on the stalk and im stuck with the lower voltage/amperage(?) Day running lights

Heres a write up of how my stalk light switch acts
twist knob resting position - drls
Twist knob first position - parking lights and drls
Twist knob second position - parking lights and drls
high beam position(forward) - no high beams no indicator on dash
Flash position(back) - high beams and indicator on dash

Extra: I did the drl wire cut modification(green and white wire iirc) naively thinking this would fix my headlight issue but it didn't change anything besides disabling the drls

What I've tried so far : replaced the stalk switch with one from Napa, replaced the dimmer relay under the hood with one from eBay, also tested the other relay right next to it with one from my mom's truck which is I think the same truck as mine, 2003 tacoma v6 with drls with the wire cut modification , looked at the filaments and they looked fine, also assuming theyre fine because drls work just not the full headlight voltage Im almost out of ideas I have access to a schematics if that's any help but im seriously thinking it's the drl control module or 'maybe' a relay located under the passenger side dash board also checked fuses

 

Just what voltage are you getting at the head light bulbs ??

You have checked the low beam fuses ??

I am guessing at one time the lights worked like they Should??

Just what happened that lead to this issue ?? The more we know the better we can try and help .

The head light switch was plug and play no chance of things not wired correct ??

You have the prints for your truck time to break out the meter and get to work remembering these are switch to ground head lights.

You did test and find the parts you replaced were defective in someway??

 

What you are looking for is on Plate 8... top left corner of each frame.

 

Wyoming09
i have checked fuses
i bought the vehicle like this
the headlight switch was plug and play
i have a meter so yes i guess thats what i'll be doing is learning how to check ground
i didnt test the parts to see if they were defective but i think i'll be swapping parts with ones from my moms truck to test it since everything works on hers

 

So, it sounds to me like you've got an issue with the low beam circuit - as it appears that that circuit never works for you.

It's unclear to me if you know this - forgive me if you do - but the DRLs work on the hi-beam circuit, simply supplying lower voltage to the hi-beam filaments. That's why your DRLs and hi-beams work - the low-beam filament is never lighting.

Follow the wires around for that low beam circuit. You'll find that somewhere you're either not getting power to the lights, or there's no ground from the lights.

In fact, that's what I'd check first - pull the plug out of the back of the headlight and there should be three female connections. One is for hi-beams and DRLs, one is for low-beams, and one is ground. Make sure that:

1. ground has continuity to the negative post of the battery/a known ground point. If it doesn't, you're looking for a problem there.
2. low-beams - gets 12V when you have the stalk set to headlights. If you don't, the problem is between the stalk and the headlights on that wire run.
3. hi-beams - gets 12V when you have the stalk set to hi-beams
4. DRL - well, those might never work if you cut the wire.

My guess is that your issue is #2. Also, the right way to disable DRLs is not to cut the white/green wire. the right way to do that is to cut a wire at the DRL relay. PM me if you want more details on that.

 

ok first i just want to thank you guys for posting any information i really appreciate it.

i've since tested the headlight plugs for any voltage and got a .25 volt readings from all three recepticles(with the headlights in on position), i bought this used fluke 87v but i dont trust it because it hunts alot with voltage but for the most part if there was 12v i think it would show it. im confused on the main drl relay, is that the drl box with the wire plug connecting to it? it doesnt look like an average relay is why im confused on it.

 

first off make sure you are using the meter correctly. You want to be on the V-DC setting. It should have a solid line with a dashed line under it. It kind of sounds like you are on V-AC. ~ is the symbol for AC on the Fluke meters.

 

yea its in v/dc with the line and dots -..

 

I would check 7.5A DRL Fuse. If this is gone the system would behave like you described.

 

Really? Why do you say that? It seems that his DRLs are the only thing "working," so I'd think that 7.5A fuse is just fine.

 

Tak it back: I just noticed: "Flash position(back) - high beams and indicator on dash" - it it works that would eliminate the fuse cause.

 

This is tricky (or stupid in Toyota naming). DRL fuse is powering relay to turn off the DRL i.e. turn on DRL relay which is bypassing the resistor i.e. giving direct short the Hi beam bulb to the ground. It is naming DRL but actually works opposite (no DRL)

 

This makes me think of that maybe this piece not working (just guessing). On the diagram listed above




The highlighted wires are responsible of for making DRL Relay to short the bulb ground (bypassing the DRL resistor).
Could be the switch, bad connector or wire issue. If you did not look at Body ECU you may check these two connectors (red-green and green-yellow wires) maybe something is odd there.

High beams work in "flash" position as they are grounding the DRL relay directly via the flash switch not via Body ECU

 

OP, I feel your pain. I have had this exact same issue with my headlights for probably 3 years. Can we rally together and find a fix here?

Here’s what I tried a while back: I had a working truck to borrow parts from and attempted a few parts swaps to see if they would solve the issue. I tried replacing the headlight relay as well as a replacement DRL unit for under the dash. Neither worked. Went ahead and ordered bulbs and a new stalk also. No fix.

edit: DRL fuse tested fine on mine also.

 

thank you jonesbt for the information about the drl relay unit, i think i can go ahead and skip the step of checking it and try to work on what RysiuM is suggesting

 

@RysiuM Curiosity got the best of me and I went to test my body ECU.

I have 12v across my r/g wire going into body ecu with selector switch in (off and —) but when switched to the headlight symbol I have 0v.

I couldn’t get to the g/y at the back of the body ECU easily so I tested the one going into the main DRL relay box and it read 12v in all positions. I assume that means the g/y checks out as ok?

 

With the Headlights OFF, the the No.4 relay is NOT in use.
With the headlights in the ON position, the HL switch provides a Ground to the No.4 relay.
Power goes from the DRL Fuse, through the control side of the No4 relay, then through the the HL switch to ground. There for, you should have a voltage on pin #13 (Red/Green wire) at the HL Switch. If you do have voltage there, then I would say the ECU is Good. I’d then make sure the Switch is good by checking continuity between pins #13 # 16 of the switch.

If you have a good switch, I’d check the ground side of the switch. Black/white wire 16 to Body Ground.

Have you checked the voltage at the HL switch?

 

Do all of your other lights work correctly? Tail, brake, rear license plate, etc..?

 

No it is not OK. R-G wire at ECU behaves like it should - it gets grounded via the light control switch in Headlight on. It should create zero Volt at G-Y wire going out of ECU. There are three options as I can see:

1. There is no continuity between 13(1L) on ECU and the G-Y wire you have tested (bad plug, chewed up wire) - I really hope it is this.

2. ECU is broken not providing ground to 13(1L) - this is possible but unlikely unless ECU got water damage or something like that. These things hardly ever go bad.

3. ECU "thinks" it should not pass the ground to 13(1L) because there is some condition on other ECU inputs. This is possible that there is some other wire, connector or switch not working correctly providing wrong information to ECU. Unfortunately I have no bloody clue what is the logic in ECU and what other conditions (inputs) might affect its behavior on 13(1L) output.

This ECU involvement in DRL was introduced in the latest models of Tacoma - I know 2000 still had direct connection between DRL relay and the light switch. It was much easier then. I suspect this is byproduct of ECU involvement in light auto turn-off when leaving the truck. But Toyota does not publish the diagram nor the functional description of ECU, so I can only guess.

 

The info in the conversation got me thinking that it is possible that ECU is just a plain hard connector with just a diode like 2000 has, with no fancy logic on other inputs. I am leaning towards that option, as it would mimic the diagram from 2000 with just moving stand alone diode into inside ECU (this is common Toyota's style ) then the most possible failure option is 1 (in my listed above). Or if the history of the truck and modifications is unknown, possible someone burned that diode in ECU (very possible if you screw up during DRL disable mod applying direct 12V to Green/Yellow wire). Base on the information from OP there is no connection between DRL relay (G-Y wire) and the switch (R-G wire), so this is a place to investigate. I would start with checking ECU (I know, it's a PITA - sorry )