ATECH 821FJ User manual

Model 821FJ
Lighting System Trainer
Supplement Service Manual
Information
2003 Chevrolet Impala
VIN W
Published by ATech Training, Inc.
12290 Chandler Drive
Walton, KY 41094 USA
Phone: [phone] Fax: [phone]
Email: [e-mail]
Website: www.atechtraining.com
Copyright 2009, ATech Training, Inc.
All Service Manual Information © General Motors Corporation

Body and Accessories
Lighting Systems
Schematic and Routing Diagrams
Headlights/Daytime Running Lights (DRL) Schematics
DRL Relay, Headlamps, and Power [w/o 6J7]
DRL Relay, Headlamps, and Power [w/ 6J7]
Indicators, and Lamp Control
Interior Lights Dimming Schematics
Dimming Control, and Steering Wheel Controls
I/P
Class 2 Dimming
Description and Operation
Exterior Lighting Systems Description and Operation
Interior Lighting Systems Description and Operation
Instrument Panel, Gages, and Console
Schematic and Routing Diagrams
Instrument Cluster Schematics
Gages, Illumination, and Indicators
Message Center
Theft Deterrent
Schematic and Routing Diagrams
Theft Deterrent System Schematics
Description and Operation
Content Theft Deterrent (CTD) Description and Operation
Doors
Description and Operation
Door Ajar Indicator Description and Operation

DRL Relay, Headlamps, and Power (w/o 6J7)

DRL Relay, Flasher, Headlamps, and Power (6J7)

Indicators, and Lamp Control

Dimming Control, and Steering Wheel Controls

I/P

Class 2 Dimming

Exterior Lighting Systems Description and Operation
Exterior Lamps
The exterior lighting consists of the following lamps:
• The Headlamps
• The Daytime Running Lamps (DRL)
• The Fog Lamps
• The Park, Tail, Licence and Marker Lamps
• The Turn Signal Lamps
• The Stop Lamps
• Special Equipment Option (SEO) Lighting
• The Backup Lamps
Headlamps
You can use the headlamps in two different ways.
•
Place the headlamp switch in the ON position for normal operation.
• Place the headlamp switch in the OFF position for automatic lamp control (ALC). During ALC the high
beam headlamps are On at reduced intensity for daytime running lamp (DRL) operation in daylight
conditions, or low beam headlamps On in low light conditions.
The DRL/EXT LTS fuse and the EXT lamps fuse in the underhood junction block supply battery positive
voltage at all times to both of low beam lamps and to the right high beam lamp. The low beam circuit
continues to the high/low beam switch, then, depending on the position of the dimmer switch, connects to
the normally-open headlamp relay switch contacts. Placing the headlamp switch in the HEAD position
provides a ground path for the headlamp switch input of the Body Control Module (BCM). After receiving
this input, the BCM energizes the headlamp relay. When the headlamp relay is energized, the low beam
circuit is connected to ground G201. The high beam circuit is divided into a left and a right side circuit.
The DRL/EXT LTS fuse in the underhood ignition block supplies battery positive voltage to both the coil
and to the normally-closed contact of the DRL relay switch circuit. During high beam operation, the left
side current flow is through the closed contacts of the DRL relay, and to the left high beam lamp.
The EXT Lamps fuse in the top of the engine fuse block supplies battery positive voltage to the right high
beam lamp. Both high beam circuits are then connected together, and continue to the dimmer switch.
When the driver closes the high beam contacts of the dimmer switch, the circuit is grounded at G201.
Both the headlight switch and the BCM provide a ground, or control circuit, to the headlight relay coil
circuit for manual or automatic headlamp operation. When you place the headlamp switch in the OFF
position, and the ambient light sensor indicates low light conditions, the BCM energizes the headlamp
relay for low beam operation. You may switch the headlights to high beam by pulling the dimmer switch
handle toward you until the dimmer switch is activated. When the dimmer switch is placed in the HIGH
position, the indicator lamp input to the BCM is pulled low. The BCM then sends a class 2 message to the
instrument cluster in order to illuminate the high beam indicator lamp.
If the headlamp switch is left in the head position, the inadvertent power control feature will turn off the
headlights 10 minutes after you turn the ignition switch to the OFF position. If you place the headlamp
switch in the head position after the ignition switch has been turned OFF, or if the ignition switch is in the
ACCY position, the headlights will remain ON until you turn them OFF or until the battery runs dead.

FTP
With the headlamps in the low beam position, you may momentarily turn ON or flash the high beams
using the dimmer switch handle. When you pull the headlamp dimmer switch handle toward you, the
flash-to-pass (FTP) switch closes, grounding the high beam circuit at G201. Both high beams will remain
ON until you release the switch handle. If the low beam headlamps were ON during an FTP operation, the
headlamps will remain ON.
Lights On Warning
The radio activates the lights on warning as requested by the body control module (BCM). The BCM sends
a class 2 message to the radio indicating the chime frequency (fast rate) and duration (continuous).
•
The ignition is OFF.
• The BCM determines that the driver's door is open (signal circuit is low).
• The BCM determines that the headlamp switch is in the park or head position.
Daytime Running Lamps (DRL)
The ambient light sensor is a light-sensitive transistor that varies its voltage signal to the body control
module (BCM) in response to changes in the outside (ambient) light level. When the BCM receives this
signal, the BCM turns ON either the DRL lamps or the headlamp relay for auto headlamp operation. Any
function or condition that turns ON the headlamps will cancel the DRL operation.
Thirty seconds after you start the ignition with the headlamp switch set in the OFF position, the DRL will
perform one of two actions:
• Illuminate the high beam headlamps at a reduced intensity in daylight conditions
•
Illuminate the low beam headlamps in low light conditions
Battery positive voltage is applied at all times from the DRL/EXT LTS fuse in the underhood junction block
to the coil side of the DRL relay. When the ambient light sensor indicates a day light condition, the BCM
applies a ground to the DRL relay control circuit. This energizes the DRL relay allowing a ground to be
applied from G101 through the DRL relay switch side to the left high beam headlamp. When the DRL relay
is energized, battery positive voltage is applied from the EXT LTS fuse through the right high beam
headlamp, to the left high beam headlamp. The high beam headlamps are now in series, and split the
voltage so that the headlamps illuminate a half intensity. The DRL operates when the ignition switch is in
the RUN position, and the parking brake is not set or the transmission is not in park. When these
conditions have been met and the ambient light sensor indicates daytime conditions, the DRL will
illuminate.
Fog Lamps
When the ignition switch is in the ON position and the headlamp switch is in either PARK or HEAD position,
the fog lights illuminate whenever you press the fog lamp switch. The FOG RLY fuse in the top of the
engine fuse block supplies battery positive voltage to both the fog lamp relay switch contacts and to the
fog lamp relay coil circuit. The fog lamp relay coil is controlled by the Body Control Module (BCM).
Whenever you press the fog lamp switch, the BCM fog lamp switch input is grounded. The BCM energizes
the control circuit of the fog lamp relay coil. The current flows from the fog lamp relay to both front fog
lamps and to ground G101. The fog lamps remain ON until you again press the front fog lamp switch, or
until you cycle the ignition switch OFF and ON. The park lamps or low beam headlamps must be ON in
order for the fog lamps to be illuminated. Fog lamp operation will be cancelled whenever the park lamps
are turned OFF or the high beam headlamps have been selected.

Park, Tail, Marker Lamps, and License
The park, tail and marker lamps, including the license lamps, turn on when the headlamp switch is placed
in either the PARK or the HEAD position, or anytime the headlamps are requested. The RT I/P #1 fuse in
the RH I/P fuse block supplies battery positive voltage to both the park lamp relay switch contacts and to
the park lamp relay coil circuit. The park lamp relay coil is controlled by the body control module (BCM).
When the headlamp switch is placed in the PARK position, the BCM energizes the park lamp relay coil
control circuit.
Current flows from the park lamp relay switch to both front and rear park lamp fuses and to their
respective park/tail lamps. The front park lamps are grounded at G101. The rear park lamps are grounded
at G302. The license plate lamps are a part of the rear park lamp circuit and are grounded at G302. The
inadvertent power control feature prevents the park lamps from remaining on more than 10 minutes if left
on. If the park lamps are turned on after the ignition switch has been turned OFF, or is in the ACCY
position, they will remain on until turned off or until the battery runs dead.
A surveillance mode is available in Special Equipment Option (SEO) vehicles. The headlamps and park
lamps may be disabled by using the emergency vehicle interior lamp switch.
Remote Keyless Entry Exterior Lamp Illumination
When the remote function actuation (RFA) module receives a door unlock command from the RFA
transmitter, the RFA module will perform the following tasks:
• Ground the door unlock signal circuit to the body control module (BCM)
• Send a class
2 message to the BCM indicating that an UNLOCK command has been received
The BCM will then flash the park lamps twice. If the doors are closed when you use the RKE transmitter in
order to lock the doors, the park lamps will flash twice. The park lamps will not flash if you use the RKE
transmitter in order to open the rear compartment.
Turn Signal Lamps
The TURN SIGNAL fuse in the LH I/P fuse block supplies ignition positive voltage to the hazard and turn
signal lamp flasher assembly. The HAZ SW fuse in the RH I/P accessory wiring junction block also supplies
battery positive voltage to the hazard and turn signal lamp flasher assembly. The turn signal lamps may
activate only when the ignition switch is in the ON or START position.
When the turn signal switch is placed in either the left or right position, current flows from the flasher
module's output to the turn signal switch assembly. The flasher module then sends an on-off voltage
signal to either the left or the right turn signals and their instrument cluster (IPC) indicator. When you
press the hazard switch, all the turn signal lamps and both of the IPC turn signal indicators will flash. The
hazard and turn signal lamp flasher assembly is grounded at G201. The front turn signals are grounded at
G101 and the rear turn signals are grounded at G302.
Turn Signal On
The Radio activates the turn signal on audible warning as requested by the body control module (BCM).
The BCM sends a class 2 message to the radio indicating the chime frequency ( fast rate) and duration (2
seconds).
Stop Lamps
The BRAKE SW fuse in the RH I/P fuse block supplies battery positive voltage to the normally-open stop
lamp switch. When you press the brake pedal the switch contacts close and battery positive voltage is

supplied to the left and right stop lamp assemblies and to the center high mounted stop lamp (CHMSL).
The left and right stop lamps along with the CHMSL are grounded at G302.
Rear Window Panel Lamps (SEO, RPO 6J6)
The rear window panel lamp system on Special Equipment Option (SEO) vehicles, consists of two red
lensed lamps that function as auxiliary turn signal and stop lamps. The wiring necessary for the additional
emergency lamps on SEO vehicles consists of battery positive voltage supplies, circuit breakers, an
emergency flasher, and relays. The lamps are mounted to the rear window panel.
Rear Compartment Lid Lamps (SEO, RPO T53)
The rear compartment lid lamps on Special Equipment Option (SEO) vehicles, consists of two red lensed
lamps that function as an auxiliary flashing warning lamp. The wiring necessary for the additional
emergency lamps on SEO vehicles consists of battery positive voltage supplies, circuit breakers, an
emergency flasher, and relays. The lamps are mounted on the inner trunk lid. When you raise the lid a
switch closes and the lamps alternately flash.
Spot Lamps and Front Lamps (SEO, RPO 9C1, 9C6, 7X6 and 7X7)
The spot lamp system on Special Equipment Option (SEO) vehicles consists of either one left spot lamp
(RPO 7X6), or two left and right spot lamps (RPO 7X7). The spot lamps are mounted to either the left or
right hand windshield pillars and contain their own ON/OFF switch. Battery positive voltage is supplied to
the spot lamps through their own respective fuses. All other wiring is blunt-ended to be used on SEO
vehicles as necessary.
Surveillance Mode Switch (SEO)
The Surveillance Mode Switch turns off the daytime running lamps (or low beam headlamps and tail lamps
during nighttime hours), instrument cluster, PRNDL and radio indicators. Interior courtesy lights are also
disabled when switch is activated.
Backup Lamps
The B/U LAMP fuse in the RH I/P fuse block supplies battery positive voltage to the switch terminal of the
backup lamps relay. The DIC/RKE fuse supplies battery positive voltage to the backup lamps relay coil
terminal. When you place the gear selector lever in the REVERSE position, the powertrain control module
(PCM) sends a class 2 message to the body control module (BCM). When these conditions occur, the BCM
energizes the reverse lamp relay control circuit, closing the switch contacts, the current flows from the
reverse lamp relay switch to the backup lamps. The backup lamps are grounded at G302.
Battery Rundown Protection / Inadvertent Power
The body control module (BCM) controls the lighting system through circuits that enable the park lamps,
head lamps and fog lamps as well as the interior lamps. The BCM opens these enabling circuits 20 minutes
after the ignition switch is turned OFF with no subsequent lamp switch activity. If the ignition switch is
turned to any position other than OFF, or if a lamp switch is activated, during this 20-minute period, the
timer will reset for another 20 minutes.
Lighting System Indicator(s)
High Beam
The IPC illuminates the high beam indicator when the body control module (BCM) detects that the high
beams are requested. The IPC receives a class 2 message from the BCM requesting illumination.

HIGHBEAM OUT
The IPC illuminates the HIGHBEAM OUT indicator in the message center when the body control module
(BCM) detects an open in one of the high beam lamp circuits. The IPC receives a class 2 message from the
BCM requesting illumination. The HIGHBEAM OUT indicator illuminates for 60 seconds when the condition
is present.
Turn Signals
The IPC illuminates the right or left turn signal indicator when the IPC detects a turn signal request or a
hazard request. If the IPC determines that the turn signal is active for more than 1.2 km (0.75 mi), the
IPC sends a class 2 message to the radio in order to activate an audible warning.

Interior Lighting Systems Description and Operation
Interior Lamps
The interior lamps consists of two groups, lamps that can not be dimmed and lamps that can be dimmed.
This first group consists of lamps that may not be dimmed. This Includes those lamps that may be
manually turned on by placing the interior lamp switch to the DOME position, or by opening a door or a
compartment:
•
Auxiliary dome lamp (SEO, RPO 6C7)
• Dome lamp
•
Inside rear view mirror lamps
•
Instrument panel (I/P) compartment lamp
• I/P courtesy lamps
• Reading lamps
• Rear compartment courtesy lamp
•
Sunshade vanity mirror lamps
Battery positive voltage is applied at all times to the DIC/RKE fuse and to the switched side of the BATT
RUNDOWN PROTECTION relay in the right I/P junction block. The DIC/RKE fuse supplies battery positive
voltage to the coil side of the BATT RUNDOWN PROTECTION relay. When the ignition is turned to the ON
position, the body control module (BCM) provides a ground to the courtesy lamp relay control circuit. This
energizes the BATT RUNDOWN PROTECTION relay and applies battery positive voltage to I/P BRP fuse and
to the TRK/ROOF/BRP fuse. Battery positive voltage is applied from the I/P BRP fuse to the I/P courtesy
lamps, I/P compartment lamp and to the courtesy lamp supply voltage circuit to the BCM. Battery positive
voltage is also applied from the TRK/ROOF/BRP fuse to the:
• Rear compartment courtesy lamp
• Dome lamp
•
Inside rear view mirror lamps
• Roof rail/reading lamps assembly
•
Sunshade vanity mirror lamps
If the BCM receives a door lock or unlock input signal, the BCM will activate the BATT RUNDOWN
PROTECTION relay, which provides battery positive voltage to all interior courtesy lamps. When any door
is opened, the door jam switch contacts close and the BCM receives a door-open input signal. The BCM
then applies a ground to the interior lamp control circuit and to the courtesy lamp low control circuit
illuminating the courtesy and dome lamps.
After all the doors are closed, the courtesy lamps remain illuminated for approximately 40 seconds. The
courtesy lamps will also turn on and remain illuminated for approximately 15 seconds after the ignition
key is removed, prior to any door being opened.
When the headlamp switch is placed in the DOME position, the BCM receives a ground signal. The BCM
then applies a ground to the interior lamps control circuit. This illuminates the dome and roof rail lamps.
The courtesy lamps will normally turn off using the theater dimming feature. The BCM provides a pulse
width modulated ground to all courtesy/reading, dome, and inside rear view mirror lamps for the theater
dimming feature. The BCM will immediately turn off the courtesy lamps if a door lock command is received
with all the doors closed, or if the ignition switch is turned to either the ON or RUN position.

The BCM activates the interior lighting output 15 seconds after receiving the class 2 message "Airbags
Deployed" from the sensing and diagnostic module (SDM). The interior lamps remain activated for
25 minutes.
Auxiliary Dome Lamp (SEO, RPO 6C7)
An auxiliary dome lamp on special equipment option (SEO) vehicles is mounted to the headliner near the
windshield. The auxiliary dome lamp is turned ON using a switch at its base.
Interior Lamps (SEO)
When the emergency vehicle interior lamp switch is turn to the OFF position, the interior lamps are
deactivated immediately.
I/P Compartment Lamp
The I/P BRP provides battery positive voltage to the instrument panel compartment lamp. When the I/P
compartment is opened, a switch closes, providing a ground circuit to G201, and the I/P compartment
lamp illuminates.
Keyless Entry Interior Illumination
When the door key is used to unlock the doors, the BCM receives a door unlock signal. The BCM activates
the interior lamps, provided the BCM has input signals indicating the following conditions:
•
The ignition switch is OFF
• The courtesy lamp switch is OFF
• All the doors are closed
If the door locks are activated to the LOCK position, or if the ignition switch is turned to either the RUN or
CRANK position the courtesy lamps turn off immediately, otherwise the courtesy lamps will remain on for
approximately 40 seconds after the door is closed. The BCM turns the courtesy lights off through the
theater dimming feature.
If the remote function actuator transmitter is used to unlock the doors or the trunk, or if the panic button
is pressed, the BCM will keep the courtesy lamps on for approximately 15 seconds. If the door locks are
activated to the UNLOCK or LOCK position, or if the ignition switch is turned to either the RUN or CRANK
position, the courtesy lamps will turn off immediately.
The BCM keeps the courtesy lamps on for approximately 40 seconds after an alarm event is completed.
The courtesy lamps in special equipment option (SEO) vehicles may be disabled by using the emergency
vehicle interior lamp switch, called surveillance mode.
Rear Compartment Lamp
The TRK/ROOF fuse provides battery positive voltage to the rear compartment lamp. When the rear
compartment is opened, the rear compartment lid ajar switch closes, providing a ground circuit to G302
and the rear compartment lamp illuminates.
Sunshade Vanity Lamps
The TRK/ROOF fuse provides battery positive voltage to each vanity mirror lamp. When the vanity mirror
cover on the sunshade is opened, a switch closes, providing a ground circuit to G302, and the vanity
lamps illuminates.

Interior Lamps Dimming
The second group of interior lighting includes lamps which may be dimmed. This group uses a combination
of class 2 controlled illumination and incandescent lamps:
• Ashtray lamp
•
Door switches and window switches
• Fog lamp switch
•
HVAC control head assembly
•
Outside rear view mirror switches
• Radio
•
Steering wheel controls
•
Instrument panel cluster (IPC)
• Traction control switch
• Headlamp switch
• Hazard switch
• Heated seat switch
•
The rear view mirror lamps
•
Surveillance mode switch (SEO, 9C1/9C3)
The RH instrument panel (I/P) fuse block supplies battery positive voltage to both the coil and normally
open switch contacts of the park lamp relay. When the body control module (BCM) energizes the park
lamp relay, current flows from the park lamp relay switched contacts through the REAR PARK LP fuse to
the I/P dimming switch. When dimming is selected, by moving the I/P dimming switch, all incandescent
back lighting lamps (see schematics) and the BCM are provided with a variable voltage through the
instrument panel lamp supply voltage #1 circuit. The incandescent back lighting lamps are then grounded
at G201, G203 and G302. The BCM then applies a message signal to the class 2 circuit to the IPC and
radio. The class 2 displays then dim to the level set by the I/P dimmer switch. When the I/P dimmer
switch is moved from MIN to MAX, all class 2 displays and all incandescent back lighting respond from
minimum intensity to maximum brightness.
Parade mode may be selected by manually turning on the park lamps during daylight conditions. The front
park lamp circuit supplies voltage the HVAC assembly for a park lamp on input, and the display will
become full bright. The BCM applies a message signal to the class 2 circuit to the IPC and radio
commanding the displays to become full bright. The surveillance mode switch (SEO) overrides this
feature.
Battery Rundown Protection / Inadvertent Power
The body control module (BCM) controls the lighting system through circuits that enable the park lamps,
head lamps and fog lamps as well as the interior lamps. The BCM opens these enabling circuits 20 minutes
after the ignition switch is turned OFF with no subsequent lamp switch activity. If the ignition switch is
turned to any position other than OFF, or if a lamp switch is activated, during this 20-minute period, the
timer will reset for another 20 minutes.

Gages, Illumination, and Indicators

MESSAGE CENTER

Theft Deterrent System Schematics