GM Service Manual Online
For 1990-2009 cars only

Headlamps - Low Beam

Voltage to the headlamp switch is available at all times through the following components:

    • The HDLP SWITCH fuse
    • The CKT 1940 (ORN) wire

When the headlamp switch is turned to the HDLP position, the headlamp power relay coil is energized through CKT 352 (WHT). A signal is sent to the body control module (BCM) that the headlamps are switched on. When the headlamp switch is in the AUTO position, a light sensor located in the right speaker grill senses one of the following conditions:

    • Daylight
    • Dark

The body control module (BCM) controls the actuation of the following components for DRL operation during a daylight condition:

    • The headlamp power relay
    • The headlamp grounding relay
    • The DRL relay

When the light sensor detects a dark condition, the BCM produces a signal that will energize only the headlight power relay, through CKT 350 (BLK) to ground G102.

The headlamp power relay supplies current to the following fuses:

    • LT HDLP
    • RT HDLP

The LH headlamp low beam bulb receives current through CKT 712 (YEL/BLK). The RH headlamp low beam bulb receives current through CKT 198 (DK BLU). Both headlamp low beam bulbs are grounded through the following components:

    • CKT 525 (YEL)
    • The underhood fuse block
    • The multifunction switch (low position)
    • The body relay block through CKT 10 (YEL) to the headlamp grounding relay

The headlamps grounding relay and the DRL relay are deenergized by the body control module (BCM). The BCM provides a ground path through the normally open contacts of the headlamps ground relay. The ground path is completed through the following components:

    • Through the underhood fuse block
    • To ground G102 through CKT 350 (BLK)

Headlamps - High Beam

Voltage to the headlamp switch is available at all times through the following components:

    • The HDLP SWITCH fuse
    • CKT 1940 (ORN)

When the headlamp switch is turned to the HDLP position, the headlamp power relay coil is energized through CKT 352 (WHT). A signal is sent to the body control module (BCM) that the headlamps are switched on. The headlamp power relay coil is grounded through the following components:

    • The underhood fuse block
    • Pin F7 of connector C2
    • CKT 350 (BLK) to ground G102

The headlamp power relay supplies current to the following fuses:

    • LT HDLP
    • RT HDLP

The RH headlamp high beam bulb receives current through CKT 198 (DK BLU) from the RT HDLP fuse. When the headlamp switch is in the HDLP position, the body control module (BCM) removes the ground path to the relay coil of the following components:

    • The headlamp grounding relay
    • The DRL relay

Both relays return to the normally open position. The normally open contacts of the DRL relay allows current to the LH headlamp high beam bulb through CKT 711 (DK GRN/WHT).

Both headlamp high beam bulbs are grounded through the following components:

    • CKT 524 (PPL)
    • The underhood fuse block
    • The multifunction switch (high position)
    • The body relay block to the headlamp grounding relay

Because the relay is deenergized, the current flows through the following components:

    • The normally open contacts of the relay
    • The underhood fuse block
    • Through CKT 350 (BLK) to ground G102

A voltage signal is sent to the body control module (BCM), through CKT 524 (PPL), to confirm proper high beam operation.