Pontiac Repair: Head Lights, marker lamps, high beams

Question


my g.p. has auto head lights not the selectable kind.the kind that comes on at night with out turning then on with then switch.what it doses is at night the low beams don't work but the parking lights and dash lights and the high beams do.and the stereo lights dim.but during the day the day time running light are on. I think those are the same as the low beam.When


I turn the switch on all light work as normal.When i turn on the high beams only the headlights turn off and back on when I turn the HBs off.So It is  some relay or that lights sensor or light switch or???.Also there a way to defeat the auto part and use them with the switch.
2000 grand prix SE base 3.1 with 157,000 on it Thank you!

Vince


Answer
Hi Vince:
This is right out of the service manual.
The Daytime Running Lamps (DRL) control module is designed to automatically operate the exterior lights depending on the outside light conditions.

The DRL control module operates in 2 modes:

   •  The day mode

        In the day mode, the DRL control module turns ON the low beam headlamps at a reduced intensity when the DRL ambient light sensor detects daylight under the following conditions:

      -  The ignition switch is in the RUN position.

      -  The headlamps are OFF.

      -  The park brake is OFF.

   •  The low light mode

        In the low light mode, the DRL ambient light sensor detects darkness, turning ON the low beam headlamps to full intensity through CKT 10.

        Additionally, the DRL ambient light sensor turns ON the following lamps through CKT 9:

      -  The park lamps

      -  The side marker lamps

      -  The license lamps

      -  The tail lamps

If the engine stalls with the DRL control module in the low light mode, the DRL control module turns OFF the headlamps while the engine is being cranked. The DRL control module turns ON the following lamps while the engine is being cranked:

   •  The side marker

   •  The park lamps

   •  The license lamps

   •  The tail lamps

The following lamps operate in the usual manner:

   •  The headlamp

   •  The instrument panel lamp dimmer switch

The DRL control module receives voltage from the following fuses:

   •  The DRL fuse through CKT 1239

   •  The DIC/HVAC fuse through CKT 541

The following lamps may be operated manually at any time by using the headlamp and the instrument panel lamp dimmer switch:

   •  The park lamps

   •  The headlamps

The DRL module does not operate if the system voltage is less than 9 volts or greater than 18 volts.

My guess here is that the lo beam headlamps have an issue wither wiring to the lamps or the DRL module or the switch is bad. It's one of them that is bad. Dumb question but they cut out at the same time right? No one lo beam and a few days later the other one? If so then it could be something as stupid as 2 blown out lo beam bulbs..