One high beam not working - 2019 Tundra

So far, I've determined that it's not bulbs, fuses, or relays. Any guidance on what to chase next would be appreciated. Thanks!

 

If you have/get techstream you could see if the BCM is receiving a signal from the high beam switch. Also you can "turn on" the highbeams with techstream to help diagnose. The combination switch for the lights is the ground for the light control. You could disconnect the headlight switch connector and find the appropriate wire the controls the high beam and the high beams should come on when grounded. This would at least eliminate the headlight switch but you will need a wiring diagram.

 

Thanks for the reply. Does what you’re suggesting apply if it’s only one headlight that won’t go to high beam?

 

No sir, this would only be if both highbeams were not working. You probably have a ground issue at the connector on the bulb. Did you check for a ground at the headlight bulb connector?

 

I’m a total rookie at trying to chase down these electrical problems. At the bulb socket, the voltage drop from the negative post to the low positive is about 12v and 0 at the high beam positive when the switch is set to low beam. When I switch to high beams, the total voltage drop is spread across both high and low beam positive posts as if they’re in parallel…. I haven’t pulled the right headlight to compare the readings yet

 

Do all your testing right at the bulb connector. The three terminals are ground, low and high. Your test light connected to ground then test for voltage at high and low terminals. Test light (not LED) should be the same brightness as when the test light is connected to the battery.

 

Sorry for the slow reply. I had to go get a test light... Here's what I've learned so far: with low beams turned on, there's voltage at the low terminal (both headlights). With high beams turned on, there's voltage at the high terminal of the right headlight and voltage at the low terminal on the left headlight (the problem headlight).

 

So when the bulbs are connected you still had a low beam on the left headlight when on highbeam?

Do you have access to the wiring diagram? If not let me know the year and model and I can see if I can find one later tonight.

 

No. When the high beams are turned on the left headlight turns off entirely. However, if I pull the LH High fuse, the LH low beam will remain on when high beams are selected.

* I do not have a wiring diagram. 2019 Tundra TSS (I think that's an SR-5 trim version)

 

I'll dig up a wiring diagram. Understanding the circuit is the first step to properly diag.

 

@cgilbertson do you have halogen or LED headlights?
Any mods done recently to any electrical in the truck?
Perhaps an OEM LED upgrade from halogen?

Here are your wiring diagrams.

 

Thank you.

FYI, when checking the plug with a multimeter here's what I find:

• Good headlight - low beams: ~12v at low terminal, 0v at high terminal
• hight beams: ~12v a high terminal, 0v at low terminal

• Bad headlight - low beams: ~12v at low terminal, ~7.5v at high terminal
• high beams: ~9v at high terminal, ~12v at low terminal

 

Thanks for the diagrams... Halogen. No electrical mods, but I did replace the front bumper so the fog light mounting is different. The harness looks like it runs down from the headlight socket to the "box" at the foglights... This started a few months after replacing the bumper. And, a few weeks later, they started working normally for a period of about 3 months. Then the problem returned.

 

This is your area of concern.
The oddest part of the situation is that it is only one side, they both get the same signal..


Is it possible a wire got pinched on that side with the bumper install?
Sounds like something is grounding the bad headlight on either beam.
Or as @Ruggybuggy stated there is a bad ground and it's grounding thru something else.
Check your bad headlight ground for continuity with a DMM.

It is going to be pin 3 white with black stripe wire





Can you check the voltage at the fuse of the problem light?

With the headlights on low with the fog lights on, the fog light is on.
What happens to the fog lights when you switch the hi beams on?
Do they both go out?

 

Also check and make sure the plug is securely seated to the headlight bulb.
I know it sounds simple, but I've done worse...

 

@1lowlife has given you very good information. I would recheck you wiring as suggested. It's likely the harness has been pinched. I was going to ask you if any body work has been done. I've repaired a few weird wiring issues of vehicles that have been in accidents and poor harness routing has caused issues.

 

• The voltage at the fuses is the same for both headlights in both high and low conditions.
• Both fog lights turn off when high beams are selected.
• I'll check continuity on that wire. However, wouldn't the problem be the same for both high and low beams since that is the ground wire for both?

*UPDATE: continuity of the ground wire at the bad headlight is good.

 

All other lights and headlight leveler work normally.
It's the driver side. The low pos wire is green, high pos wire is blue.

 

Is this one of the models / years that had the headlight harness recall?

 

I was hoping that was it. But, a vin search shows no recalls for mine.

 

OMG...............
Although he only has it on one side.
That is the confusing part...

RCMN-21V688-9434.pdf (nhtsa.gov)

 

The TSB is a condition where both high beam and low beam are on at the same time so unless the connector at the bulb has melted then this shouldn't apply.

 

Is that not what we're seeing here??

 

He only has a problem with the left side highbeam not coming on. The tsb is for both highbeams coming on with the low beams causing the bulb connectors to overheat and melt.

 

I was kind of wondering the same thing. There's always voltage at the high beam terminal. However, I don't ever see both elements illuminated at the same time.

BTW, my truck manufacture date falls within the recall period. But, when I do a search by VIN or license plate number, it doesn't indicate that my vehicle has a recall. I'm not the first owner. I owned the vehicle for about a year when the problem first occurred.

 

When something is designed poorly and prone to fail, we don't always get the exact same failure pattern or a full failure every time. This is still the symptoms associated with the known harness issue. I wouldn't rule it out. The variable here is the bumper lights swap and the fact that the symptoms were closely related in time to that. I would retrace that and see if there is an issue there first if it were me. Then I would chase down the harness recall issue.

 

Could it be the harness is bad? Is it possible / easy to get a new harness and try that first? To my very novice eyes, It seems that there must be a wire pinched somewhere or that the harness is bad.

 

I'll try to trace that blue wire and see if I can find anything unusual. And, I'll also swing by a dealer and see if perhaps my vehicle should've been part of the recall, or if the recall remedy has already been done on my truck.

 

I'm probably much more novice than you. When I search for harnesses, most of the results are for plug-and-play LED upgrade kits or ads from findpigtails.com. Any pointers on how to correctly search for a replacement are welcomed.

 

Its likely that the harness is a long run and very involved (and expensive). I was more under the assumption that you may have used a relocation harness for the bumper and maybe that was the culprit.