Passenger DRL does not turn on when headlights turn on

Hello! New 2018 Tacoma owner here! Loving the truck so far. The only thing I've noticed so far is there is something wrong with the passenger side DRL light. Both driver and passenger DRL turn on just fine in DRL mode. Both blinkers also work fine. However, when I turn my low beams on, only the driver side DRL stays on and the passenger one does not come on at all. As mentioned, the light works otherwise, so I don't think it's the bulb. I also checked the DRL fuse under the hood and that is fine and intact. Is there a relay fuse or switch for it somewhere? Or some kind of settings I can toy with?

 

@haoleflip What trim is the truck?

 

SR5 double cab v6

 

That helps I am willing to bet it is the bulb. The SR5 uses a 7442 which is a dual filament bulb. The high filament is used for DRL with the low beams off and turn signal, while the low filament is used for DRL with the low beam on. If you wanted to verify this, you can swap bulbs side to side. The problem should follow the bulb if it is the bulb.

 

Ok thank you for your reply! I will try to switch the bulbs around first.

 

If that doesn’t fix it, let me know and we can do some further troubleshooting, but I’m pretty sure that will be your issue

 

I switched the bulbs just now and it is exactly what you said! Going to buy a new one now. Thanks again!

 

I thought DRL is off once you switch headlights on? So it would be the Drivers side bulb that is incorrect? You should be able to see in the bulb that it has dual filaments.

 

Are they supposed to turn off when headlights come on? I just assumed they were both supposed to be on since one of them stayed on. When I switched bulbs, the working bulb that was on my passenger side illuminated on the driver side.

 

Are there 2 nubs on the base of the bulb? Ie means there are two filaments. Can you see inside the bulb? You want the type with 2 filaments. Check the part# often at the base of the glass, or stamped onto the metal of the bulb base.

 

Yes, they do have 2 in each bulb.

 

And same part# then?

 

Yes both are 7442NA. Same bulbs.

 

Yup, getting a new bulb worked! Thanks!

 

I’ve always switched both out when 1 goes bad . From my experience it’s not gonna be long before the other starts acting up. I also use a small dab of dielectric grease to help with corrosion and moisture.

 

When the DRL (actual DRL, there is a difference) is on, the bulb lights up at full brightness (28W filament). The turn signal also lights up that same 28W filament. When the low beam is on, the power to the 28W filament is shut off (except for when the turn signal is activated) and the bulb uses the parking (or running light circuit, whatever you'd like to call them) to power the dimmer 8W filament. So the bulb is still lit up, just dimmer. The TRD models do the same thing with the LED DRL (the halogen version as well as the full LED version), but those have a separate white DRL that dims to less bright white when the low beams are turned on. Hope that makes sense.

So the breakdown is something like this for the SRs with a type B stalk switch. The type A is functionally the same as long as it is light outside, so AUTO would replace DRL in that case:

Stalk setting | Turn signal on/off | DRL bulb wattage |
OFF OFF 0W (off)
OFF ON 0/28W pulse
DRL OFF 28W steady
DRL ON 28W/0W/28W pulse, full brightness basically gets broken up with an off signal
PARKING OFF 28W steady
PARKING ON 28W/8W/28W pulse, full brightness basically gets broken up and the light goes dim between pulses, but returns full brightness after the turn signal is turned off
LOW BEAM OFF 8W steady
LOW BEAM ON 8W steady, 28W pulse with turn signal

 

Not a bad practice.