Principles of Operation

Interior Lighting

Principles of Operation

The Body Control Module (BCM) controls all the interior lighting functions and timing by monitoring inputs from the following:

- door ajar switches
- ignition state
- instrument panel dimmer switch (monitored by the Steering Column Control Module (SCCM))
- Remote Keyless Entry (RKE) system
- vehicle speed

The BCM turns off the courtesy lamps when the vehicle speed exceeds 15 km/h (9 mph) or 5 km/h (3 mph) for the puddle lamps, unless the courtesy lamps are turned on using the instrument panel dimmer switch.

Interior Lamp Arbitrator

The interior lamp arbitrator (programming within the BCM) chooses between the interior lighting delay, the illuminated entry and exit, the battery saver, and the alarm flash processing to determine which feature has precedence of activating and deactivating the interior lamps.

Ambient Lighting

The Interior Lighting Control Module (ILCM) provides voltage and ground to the LEDs. There are 3 different color LEDs (red, blue and green) housed within each LED assembly. By illuminating various color combinations, the LEDs can produce 7 different colors of ambient light. The ambient lighting select switch and ambient lighting dimmer switch are inputs to the ILCM. With each press of the ambient lighting select switch, the ILCM cycles through a different color variation or turns the ambient lighting feature off. With each press of the ambient lighting dimmer switch, the ILCM changes the brightness setting of the ambient lighting. The module retains the last color and brightness setting between uses.

The ILCM also receives messages regarding courtesy lamp door ajar status, illuminated entry status, accessory delay status, courtesy lamp delay status, battery saver relay status and ignition status over the network from the BCM. The ILCM uses these inputs to determine when the ambient lighting is turned on to the preset color and brightness setting or to customer-selected color and brightness setting. The color and brightness setting can only be changed when the ignition is in RUN or ACC, the parking lamps are on and all of the doors are closed.

Field-Effect Transistor (FET) Protection

A Field-Effect Transistor (FET) is a type of transistor that, when used with module software, monitors and controls current flow on module outputs. The FET protection strategy prevents module damage in the event of excessive current flow.

The BCM utilizes an FET protective circuit strategy for many of its outputs (for example, a headlamp output circuit). Output loads (current level) are monitored for excessive current (typically short circuits) and are shut down (turns off the voltage or ground provided by the module) when a fault event is detected. A short circuit DTC is stored at the fault event and a cumulative counter is started.

When the demand for the output is no longer present, the module resets the FET circuit protection to allow the circuit to function. The next time the driver requests a circuit to activate that has been shut down by a previous short (FET protection) and the circuit is still shorted, the FET protection shuts off the circuit again and the cumulative counter advances.

When the excessive circuit load occurs often enough, the module shuts down the output until a repair procedure is carried out. Each FET protected circuit has 3 predefined levels of short circuit tolerance based on the harmful effect of each circuit fault on the FET and the ability of the FET to withstand it. A module lifetime level of fault events is established based upon the durability of the FET. If the total tolerance level is determined to be 600 fault events, the 3 predefined levels would be 200, 400 and 600 fault events.

When each tolerance level is reached, the short circuit DTC that was stored on the first failure cannot be cleared by a command to clear the continuous DTCs. The module does not allow this code to be cleared or the circuit restored to normal operation until a successful self-test proves that the fault has been repaired. After the self-test has successfully completed (no on-demand DTCs present), DTC U1000:00 and the associated DTC (the DTC related to the shorted circuit) automatically clears and the circuit function returns.

When each level is reached, the DTC associated with the short circuit sets along with DTC U1000:00. These DTCs are cleared using the module on-demand self-test, then the Clear DTC operation on the scan tool (if the on-demand test shows the fault corrected). The module never resets the fault event counter to zero and continues to advance the fault event counter as short circuit fault events occur.

If the number of short circuit fault events reach the third level, then DTCs U1000:00 and U3000:49 set along with the associated short circuit DTC. DTC U3000:49 cannot be cleared and the module must be replaced after the repair.

The BCM FET protected output circuits for the interior lighting system are the interior courtesy lamp and puddle lamp output circuits.