Headlamps

Headlamps

Principles of Operation

NOTE: The Smart Junction Box (SJB) is also known as the Generic Electronic Module (GEM).

NOTE: The Headlamp Control Module 2 (HCM-2) is also known as the automatic high beam module.

Exterior Lighting

The SJB (Smart Junction Box) monitors the headlamp switch position by sending voltage reference signals on multiple circuits to the headlamp switch. There is one circuit for each headlamp switch position. At any given time, one of the signal circuits is switched to ground.

If the SJB (Smart Junction Box) does not detect any of the inputs to the headlamp switch are active (switched to ground) for 5 seconds, the SJB (Smart Junction Box) turns on the parking lamps and headlamps and keeps them on until the battery saver feature times out.

Additionally, if the SJB (Smart Junction Box) detects multiple headlamp switch input circuits short to ground, the SJB (Smart Junction Box) turns on the parking lamps and headlamps and keeps them on until the battery saver feature times out.

Refer to Exterior Lighting Exterior Lighting for information regarding the Battery Saver feature.

If either of these situations occur, the SJB (Smart Junction Box) Cannot be ruled immediately as being at fault. This is normal behavior of the SJB (Smart Junction Box) design as it has detected a fault with the inputs from the headlamp switch.

The SJB (Smart Junction Box) also monitors the multifunction switch for a flash-to-pass or high beam request. There are 2 voltage reference circuits which monitor this. When the multifunction switch is in the FLASH-TO-PASS or HIGH BEAM position, the voltage signal is routed to ground.

NOTE: The flash-to-pass feature does not require any input from the headlamp switch.

When the SJB (Smart Junction Box) receives an input requesting the headlamps on, the SJB (Smart Junction Box) supplies voltage to the headlamp relays in the Battery Junction Box (BJB) (halogen headlamps) or a ballast within each headlamp (High Intensity Discharge (HID)). For halogen headlamps, the headlamp relays then energize and route voltage to the headlamps. For HID (High Intensity Discharge) headlamps, the ballasts then provide the necessary voltage to the HID (High Intensity Discharge) bulbs.

High Beam Functionality

When the high beams are requested, the headlamps remain powered and a shutter within each headlamp is activated. This changes the headlamp beam pattern to illuminate a greater distance.

The flash-to-pass feature is different between vehicles equipped with halogen headlamps and vehicles equipped with HID (High Intensity Discharge) headlamps. If the low beams are off when the flash-to-pass is requested, the headlamps and the shutters are activated for approximately 2.2 seconds on halogen headlamps equipped vehicles and approximately 0.5 second on HID (High Intensity Discharge) headlamp equipped vehicles. If the low beams are on when the flash-to-pass is requested, the shutters within the headlamps are activated as long as the multifunction switch is held in the FLASH-TO-PASS position.

Automatic High Beams

The HCM-2 (Headlamp Control Module 2) controls the automatic high beam feature when active. The HCM-2 (Headlamp Control Module 2) turns the high beam headlamps on when the following conditions are met:

- the feature has been enabled using the message center

- the autolamps feature has turned the exterior lamps on

- the vehicle speed is greater than 51 km/h (32 mph)

- the HCM-2 (Headlamp Control Module 2) determines the ambient lighting conditions are dark enough

- the HCM-2 (Headlamp Control Module 2) does not detect any light source that may be interpreted as an illuminated vehicle lamp

The HCM-2 (Headlamp Control Module 2) turns the high beams off if any of the following occur:

- the HCM-2 (Headlamp Control Module 2) detects any light source that is interpreted as an illuminated vehicle lamp

- the HCM-2 (Headlamp Control Module 2) determines the ambient lighting conditions are not dark enough

- the vehicle speed falls below 44 km/h (27 mph)

- the fog lamps are turned on

- the autolamps are turned off

- the HCM-2 (Headlamp Control Module 2) determines the view is blocked

When the HCM-2 (Headlamp Control Module 2) determines that the high beams need to be turned on, the HCM-2 (Headlamp Control Module 2) sends a message over the communication network to the SJB (Smart Junction Box) to turn the high beams on.

The HCM-2 (Headlamp Control Module 2) defaults to the low beams when the following DTCs are present:

- B11C7:46

- B11C7:97

Field-Effect Transistor (FET) Protection

Field-Effect Transistor (FET) is a type of transistor that when used with module software can be used to monitor and control current flow on module outputs. The FET (Field-Effect Transistor) protection strategy is used to prevent module damage in the event of excessive current flow.

The SJB (Smart Junction Box) utilizes a FET (Field-Effect Transistor) 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 continuous 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 (Field-Effect Transistor) 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 (Field-Effect Transistor) protection) and the circuit remains shorted, the FET (Field-Effect Transistor) 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 (Field-Effect Transistor) protected circuit has 3 predefined levels of short circuit tolerance based on the harmful effect of each circuit fault on the FET (Field-Effect Transistor) and the ability of the FET (Field-Effect Transistor) to withstand it. A module lifetime level of fault events is established based upon the durability of the FET (Field-Effect Transistor). 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 continuous 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 B106E and the associated continuous DTC (the DTC related to the shorted circuit) automatically clears and the circuit function returns.

When the first or second level is reached, the continuous DTC (associated with the short circuit) sets along with DTC B106E. These DTCs can be 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 B106F and B1342 set along with the associated continuous DTC. This DTC cannot be cleared and the module must be replaced.

The SJB (Smart Junction Box) FET (Field-Effect Transistor) protected output circuits for the headlamp system are the LH low beam output and the RH low beam output circuits.