1999 Grand Prix GT Coupe Daytime Running Lights wont come on anymore

I can't pull up a schematic right now, so bear with a generic answer. I am pretty certain that your car uses series beams for DRL function i.e. either the low beams or high beams are rewired in series using relays or the BCM to send half voltage to each, thus making them appear less bright in DRL mode. BOTH filaments used in the DRL system must be working for them to light up when wired in series.

Be certain that both low and both high beams operate in "normal" mode before wasting any diagnostic time.

If you have amber or otherwise dedicated bulbs for DRL, then ignore the above and test bulbs, relays, then wiring in that order.

Toyota MDT in MO

I forgot to mention that your parking brake input will cancel DRLs by design. Is the brake warning light on in the dash?

Toyota MDT in MO

Thanks..

No brake warning light on..

I'm pretty certain my high beams are working correctly too at this point though.

I thought maybe there was a daytime sensor of some kind (Sorry, I'm not very car knowledgeable.. more of a PC tech kinda person)..

Yes. ALSO there is a DRL relay, which switches the lamps in series onto a seperate power source with a seperate fuse. That relay is activated by the DRL module.

Check the DRL fuse under the dash before anything else, then check the relay.

--scott

I guess my last big, long-winded post was lost in cyberspace, so I will recap briefly.

I finally got to see the schematics for your DRL system. Your design does not series bulbs together as I had guessed earlier. There are no relays in the system. The low beams are used along with an inline current reducer for DRL operation. Your likely culprit is the current limiting device known as the "DRL Diode". An easy test to prove this part out is as follows:

• Get your system into DRL mode (parking brake off, start engine, parked in bright sunlight, headlight switch in "OFF" position -- sometimes called "AUTO" on DRL systems).

• Locate the DRL Diode. My component locator shows it to be a smallish square part that is completely covered in cooling fins. It has a two wire connector. It is located under/behind the dash on the far left side. It appears to be just to the left of a trio of relays arranged on top of one another.

• Assuming the DRLs are currently nonfunctional (no light at all from headlights) unplug the DRL Diode connector and jumper its two wires together. If the low beams light up at full intensity, then your problem is the DRL Diode.

Do this check before any more troubleshooting, as it is a very likely cause of your symptoms.

Toyota MDT in MO

We'll assume that the DRL diode assembly was the culprit. Using "we", I can single-handedly make an ass out of everyone with just one statement.

Case automatically closed Reason: time expired

Toyota MDT in MO