For 1990-2009 cars

## Headlights/Daytime Running Lights (DRL) Circuit Description Chevrolet and Pontiac/Canadian

The Daytime Running Lamps (DRL) module is designed to automatically operate the exterior lights depending on the outside light conditions.

The DRL module operates in 2 modes:

• | The day mode

| In the day mode, the DRL 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 tail/stop lamps

- | The license lamps

- | The tail lamps

- | The park/turn lamps

- | The tail/stop/turn lamps

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

• | The park/turn lamps

• | The park lamps

• | The license lamps

• | The tail lamps

• | The tail/stop lamps

• | The tail/stop/turn lamps

The following lamps operate in the usual manner:

• | The headlamp

• | The instrument panel lamp dimmer switch

The DRL module receives voltage from the following fuses:

• | The TAIL LPS fuse through CKT 240

• | The TURN B/U fuse through CKT 141

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.

### Daytime Running Lamps (DRL) Ambient Light Sensor

The DRL ambient light sensor is a light sensitive variable resistor. The DRL ambient light sensor's resistance decreases as the outside light intensity increases. The DRL module performs the following functions:

• | Measures the voltage drop across the DRL ambient light sensor.

• | Determines whether the DRL ambient light sensor should operate in the day mode or the low light mode.

### Park Brake Input

The DRL module will not operate any headlamps or exterior lamps if the park brake is applied before the ignition switch is turned to the RUN position. This allows the driver to start the vehicle and keep the headlamps OFF, as long as the park brake is applied. The DRL module activates the headlamps when the park brake is released with the ignition switch in the RUN position. This feature functions only when the park brake is applied before the ignition switch is turned to the RUN position. The headlamps will not turn OFF, if the park brake is applied after the ignition switch is turned to the RUN position.

## Headlights/Daytime Running Lights (DRL) Circuit Description Pontiac Domestic

### Daytime Running Lamps (DRL)

The Daytime Running Lamps (DRL) module is designed to automatically operate the exterior lights depending on the outside light conditions. The ambient light sensor is replaced by a jumper.

The DRL module operates when the following occurs:

• | The ignition switch is in the RUN position.

• | The headlamps are OFF.

• | The park brake is OFF.

The DRL module applies voltage to the front turn signal bulbs. Whenever the left or the right turn input is received at the DRL module, the front turn signal bulbs operate normally. When the park lamps or the head lights are on, the DRL removes voltage from the front turn bulbs.