no low beam but drls work

Yes if the No4 Relay is good, and there is nothing on the G-Y wire, I too would suspect a diod or ECU.

 

Did you test (or look) if 2003 ECU indeed has just a diode between 13(1L) and 14(1L). I know for the fact that Toyota is very reluctant to any changes in their vehicles within the same model. Their Change management is so strict almost like in airplane manufacturers. So it is most likely that they did not introduce any new functional logic in that area, just shoved in that stand alone diode.

 

I have no way to test it. I own a 2007.
And the diagrams I have don’t show anything inside the ECU.
The 2003 diagram still show a diod separate from the ECU.

PM inbound

 

Thanks. 2000 (and earlier) don't have ECU but have two diodes separating Flash from Headlight. The diagram looks different but the functionality is very identical.

 

Oh, ok.
I only have access to 01’ and 03’ diagrams.

 

@turbodb
@RysiuM
@jonesbt

This headlight issue is solved, according to the mechanic its a bad B-ECU. the work around was shorting the switch past the body ecu, i'll post some pictures of what was crimped together if jonesbt is still having this issue.

thank you everyone for the advice you guys were spot on in your troubleshooting but im just inexperienced in electrical.

 

Photos would be great. Thanks for following up! I actually actuated a new body ECU a couple of days ago but haven’t attempted to install it yet.

 

I’m having the same problem on my 04 Tacoma. No low or high beams when switch is turned on. DRL’s are functioning properly, and headlights work in the flash position. Fuses and relays checked good. I have 12 volts at body ecu connector green/yellow wire but 0 volts at the red/green wire and 0 volts at pin 13 of the switch. I’m thinking it may be a problem within the body ecu. Is there any way to test it to be sure? Any help would be appreciated.

 

Update: Problem resolved. I ended up replacing the Body ECU (fuse/junction-block assembly).