For 1990-2009 cars

### Circuit Description

The body control module (BCM) activates the headlamp relay when the light sensor senses a dark condition. Battery voltage is supplied to the headlamp relay through the BACKUP/TURN fuse locate in the UHFB. The BCM provides ground to circuit 352 to activate the headlamp relay; if the headlamp relay control circuit is shorted to battery for one second DTC B2578 will fail as current.

### Conditions for Setting the DTC

• | The headlamp relay is commanded ON.

• | Short to battery

• | Ignition in RUN

• | The condition is present for 1 second.

• | No light will illuminate in the instrument panel (I/P).

### Diagnostic Aids

• | Check for poor connection at the BCM. Inspect harness connectors for backed-out terminals, improper terminal mating, broken connector locks, improperly formed or damaged terminals and poor terminal-to-wire connection -- terminal crimped over wire insulation and not conductors.

• | Inspect the wiring harness for damage. Inspect for broken or chaffed insulation.

• | If fault is suspected to be intermittent, wiggling the harness wiring may help in locating fault.