Interior Lighting System: Overview Mercury Sable V

Note. The smart junction box (SJB) is also known as the generic electronic module (GEM).

The interior lighting system consists of the following components

1. Door ajar switches
2. Instrument panel dimmer switch
3. Interior/map lamps
4. Luggage compartment lamp (if equipped)
5. Luggage compartment/liftgate ajar switches (part of the latch assembly)
6. Liftgate/trunk module (LTM) (if equipped)
7. Puddle lamps
8. SJB
9. Vanity mirror lamps

The interior lighting system consists of 2 subsystems

1. Courtesy lamps
2. Demand lamps

The courtesy lamps are controlled by the SJB. The courtesy lamp subsystem consists of the ajar switches, interior dome lamps, LTM (if equipped), and the puddle lamps. The SJB supplies voltage to the courtesy lamps when the SJB receives the required input.

The demand lamps are also controlled by the SJB via the battery saver relay. The demand lamps subsystem consists of the instrument panel dimmer switch, luggage compartment lamp (if equipped), all map/reading lamps, and the LH and RH vanity mirror lamps. The SJB energizes the battery saver relay to supply voltage to the demand lamps.

The SJB and the LTM (if equipped) set DTCs if certain circuit failures exist with the interior lighting system.

Special Tools Illustration Tool Name Tool Number 73III Automotive Meter 105-R0057 or equivalent Vehicle Communication Module (VCM) and Integrated Diagnostic System (IDS) software with appropriate hardware, or equivalent scan tool Flex Probe Kit 105-R025C or equivalent

Scheme 1

Scheme 2

Principles of Operation

Note. The smart junction box (SJB) is also known as the generic electronic module (GEM).

The SJB supplies voltage to the interior lighting system. The interior lighting system illuminates the courtesy lamps to enhance visibility of the interior while a vehicle door is ajar, and the vehicle speed is less than 15 km/h (9 mph) or 5 km/h (3 mph) for puddle lamps. The SJB controls all interior lighting functions and timing by monitoring inputs from the door ajar switches, the instrument panel dimmer switch, and vehicle speed.

Normal Operation

Power is supplied to the courtesy lamps through the smart junction box (SJB) fuse 9 (15A). When any door or the liftgate is opened, the ajar switch opens, signaling the SJB. The SJB monitors the ajar circuits and IKT input. Based on the input status, the SJB supplies voltage to the courtesy lamps on circuit VLN33 (GY/VT). Ground is supplied through circuits GD133 (BK) and GD147 (BK/VT) for the courtesy lamps.

1. DTC B2A35 (Interior Lighting Output Circuit Open) - is an on-demand DTC that sets when the SJB detects an open from the interior lighting circuit.
2. DTC B2A36 (Interior Lighting Output Circuit Short To Ground) - is a continuous and on-demand DTC that sets when the SJB detects a short to ground from the interior lighting circuit.

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. SJB

When any door or the liftgate is opened, the ajar switch (or the liftgate/trunk module [LTM] if equipped) opens the circuit to the smart junction box (SJB) to indicate a request for the courtesy lamps. When the instrument panel dimmer switch is rotated to the dome detent, ground is supplied on circuit CLN28 (GN/BU) to the SJB. The SJB monitors the ajar circuits and the dome input circuit. Based on the inputs, the SJB supplies voltage to the courtesy lamps on circuit VLN33 (GY/VT).

This pinpoint test is intended to diagnose the following

1. Wiring, terminals or connectors
2. Door ajar switch
3. Liftgate ajar switch
4. Instrument panel dimmer switch (part of the headlamp switch)
5. LTM
6. SJB

Based on the input status, the smart junction box (SJB) supplies voltage to the courtesy lamps on circuit VLN33 (GY/VT). Ground is supplied through circuits GD133 (BK) and GD147 (BK/VT) for the courtesy lamps.

This pinpoint test is intended to diagnose the following

1. Wiring, terminals or connectors
2. Interior lamp

When any door is opened, the door ajar switch opens the circuit to the smart junction box (SJB). The SJB monitors the door ajar circuits, and based on the status, the SJB supplies voltage to the courtesy lamps on circuit VLN33 (GY/VT).

This pinpoint test is intended to diagnose the following

1. Wiring, terminals or connectors
2. Door ajar switch
3. SJB

When the liftgate is opened, the liftgate ajar switch (or liftgate/trunk module [LTM], if equipped) opens the ground signal to the smart junction box (SJB) through circuit CPL58 (GY/OG). The SJB monitors the liftgate ajar circuit, and based on the ajar status, the SJB supplies voltage to the courtesy lamps on circuit VLN33 (GY/VT).

1. DTC B2721 (Liftgate/Decklid Ajar Output Short To Ground Or Open) - is a continuous and on-demand DTC that sets when the LTM detects a short to ground from the liftgate ajar input circuit to the SJB.

This pinpoint test is intended to diagnose the following

1. Wiring, terminals or connectors
2. Liftgate ajar switch (part of the liftgate latch)
3. Rear wiper motor
4. LTM
5. SJB

The smart junction box (SJB) monitors the instrument panel dimmer switch status on circuit CLN28 (GN/BU) to determine if the courtesy lamps are requested. When the instrument panel dimmer switch is rotated to the dome detent, ground is supplied to circuit CLN28 (GN/BU). Based on the dimmer switch status, the SJB supplies voltage to the courtesy lamps through circuit VLN33 (GY/VT).

This pinpoint test is intended to diagnose the following

1. Wiring, terminals or connectors
2. Instrument panel dimmer switch (part of the headlamp switch)
3. SJB

The smart junction box (SJB) provides voltage to the puddle lamps through circuit CLN25 (VT). The puddle lamps have separate ground circuits. The LH exterior mirror is grounded through circuit GD133 (BK), and the RH exterior mirror is grounded through circuit GD148 (BK/YE).

1. DTC B2A39 (Puddle Lamp Output Circuit Open) - is an on-demand DTC that sets when the SJB detects an open on the puddle lamp output circuit.
2. DTC B2A3A (Puddle Lamp Output Circuit Short To Ground) - is a continuous and on-demand DTC that sets when the SJB detects a short to ground on the puddle lamp output circuit. This DTC also sets as a result when the SJB fuse 10 (15A) has failed or is removed.

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. Exterior mirror
4. Puddle lamp
5. SJB

The smart junction box (SJB) provides voltage to the puddle lamps through circuit CLN25 (VT). The puddle lamps have separate ground circuits. The LH exterior mirror is grounded through circuit GD133 (BK), and the RH exterior mirror is grounded through circuit GD148 (BK/YE).

1. DTC B2A39 (Puddle Lamp Output Circuit Open) - is an on-demand DTC that sets when the SJB detects a short to voltage on the puddle lamp output circuit.

This pinpoint test is intended to diagnose the following

1. Wiring, terminals or connectors
2. SJB

The smart junction box (SJB) energizes the battery saver relay based on inputs from the ignition key position, ajar switches, integrated keyhead transmitter (IKT), keypad, and the instrument panel dimmer switch (when rotated to the dome position). When the battery saver relay is energized, it supplies voltage to the demand lamps on circuit CLN09 (YE/GN). The demand lamps are grounded through circuits GD133 (BK) and GD147 (BK/VT).

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. SJB

The smart junction box (SJB) supplies voltage to the demand lamps on circuit CLN09 (YE/GN). The demand lamps are grounded through circuits GD133 (BK) and GD147 (BK/VT).

This pinpoint test is intended to diagnose the following

1. Wiring, terminals or connectors
2. Interior lamp

The smart junction box (SJB) supplies voltage to the luggage compartment lamp on circuit CLN09 (YE/GN). The luggage compartment lamp ground is a series circuit that is comprised of circuits GD147 (BK/VT), CLN13 (WH/BU), and the luggage compartment ajar switch (part of the luggage compartment lid latch). When the luggage compartment lid is ajar, the ajar switch closes and completes the ground path by connecting circuit GD147 (BK/VT) to circuit CLN13 (WH/BU).

1. DTC B1331 (Decklid Ajar Rear Door Circuit Failure) - is an on-demand DTC that sets when the SJB detects an open from the luggage compartment ajar input circuit to the SJB.

This pinpoint test is intended to diagnose the following

1. Wiring, terminals or connectors
2. Luggage compartment lamp
3. Luggage compartment lid latch

The smart junction box (SJB) provides a battery saver function. The battery saver function provides automatic shutoff of the interior lamps (courtesy lamps and demand lamps) after 10 minutes has elapsed in order to save battery power.

This pinpoint test is intended to diagnose the following

1. Wiring, terminals or connectors
2. SJB