Turn Signal Lamp: Description and Operation

TURN SIGNAL LAMPS




The smart flasher (GMSF) is an automotive flasher designed to accept turn, hazard, and brake inputs. The GMSF will provide corresponding outputs to the exterior lamps and instrument panel turn signal indicator lamps. This lighting system has combined lamps for the turn/hazard functions and the brake function. The system incorporates the use of flash rates for diagnostics. The flash rate is a calculation of the number of flashes that occur within a 60 second period. This system uses a percentage of on-time to off-time called duty cycle. For the bulb outage condition, the indicator of the vehicle side on which the outage occurs shall assume bulb outage flash rate mode. The opposite side indicator will assume the normal flash rate mode for an input from the non bulb outage side of the vehicle. Hazard warning lamp outage will maintain a normal flash rate as long as 2 or more exterior signaling lamps are functional. During all modes of operation, the instrument panel cluster (IPC) will receive the same flash rates and duty cycles that the exterior lamps receive. The IPC will then control the indicators in the cluster. The vehicle operator will be provided with an audible and visual indication of the flasher operation. There is a table with flash rates and duty cycles.

The IGN E fuse in the underhood fuse block supplies Ignition positive voltage to the turn signal switch assembly. With the ignition switch in the RUN or START position, ignition positive voltage is connected through the turn signal/multifunction switch assembly to the GMSF which is powered by the FLASH fuse also in the underhood fuse block and is grounded at G200. When the turn signal switch is placed in either the left or right position, the circuit is completed from the GMSF to the turn signal lamps and to ground. The GMSF then sends an ON-OFF voltage signal to either the left or right turn signals and their IPC indicator. When the hazard switch is pressed, all turn signal lamps will flash including both IPC turn indicators. The front turn signals are grounded at G105 and G100. The rear turn signals are grounded at G402.

The IPC illuminates the TURN SIGNAL ON indicator in the driver information center when the IPC determines that the turn signal is active for more than 1.2 km (0.75 mile). The IPC also sends a class 2 message to the radio in order to activate the audible warning.

For trailer wiring, the turn signal circuits are also connected to the trailer wiring harness.