GM Service Manual Online
For 1990-2009 cars only

Front Fog Lamps

When the ignition switch is in the RUN position, battery positive voltage (B+) is applied to the coil of the fog lamp relay in the underhood relay center from the IGN 1 fuse via CKT 439 (PNK). Battery positive voltage (B+) is applied at all times to the switch side of the fog lamp relay from the FOG LAMPS fuse via CKT 1640 (ORN). When the front fog lamps switch is enabled, the instrument cluster front fog lamps input is grounded through the headlamp switch via CKT 192 (ORN). In response to this input the instrument cluster sends a request via the Class 2 serial data line to the body control module (PZM) to activate the front fog lamps. The PZM provides ground for the coil via CKT 1317 (DK GRN/WHT). The coil is then energized, closing the switch contacts. Battery positive voltage (B+) is then applied via CKT 34 (PPL) to the fog lamps and the front fog lamps ON indicator. The PZM also activates the park lamps when the front fog lamps are on. When the front fog lamps are enabled and the high beams or flash-to-pass are activated, the front fog lamps will be temporarily disabled for as long as the high beams or flash-to-pass are enabled. The park lamps will remain on during this period.

Rear Fog Lamps

When the ignition switch is in the RUN position, battery positive voltage (B+) is applied to the coil of the rear fog lamp relay from the IGN 1 fuse via CKT 439 (PNK). With the park lights on, battery positive voltage (B+) is applied to the switch of the rear fog lamp relay from the RT PARK fuse via CKT 9 (BRN). When the rear fog lamps switch is enabled, the instrument cluster rear fog lamps input is grounded through the headlamp switch via CKT 187 (LT BLU). In response to this input, the instrument cluster sends a request via the Class 2 serial data line to the body control module (PZM) in order to activate the rear fog lamps. The PZM provides ground for the coil via CKT 1977 (YEL). The coil is then energized closing the switch contacts. Battery positive voltage (B+) is then applied via CKT 122 (RED) to the LH and RH rear fog lamps, and the rear fog lamps ON indicator.