2006 MERCEDES-BENZ SPRINTER remote control

3.2.2 ECM OPERATING MODES
As input signals to the ECM change, the ECM
adjusts its response to the output devices. For
example, the ECM must calculate a different fuel
quantity and fuel timing for engine idle condition
than it would for a wide open throttle condition.
There are several different modes of operation that
determine how the ECM responds to the various
input signals.
Ignition Switch On (Engine Off)
When the ignition is turned on the ECM activates
the glow plug relay for a time period that is deter-
mined by engine coolant temperature, intake air
temperature and battery voltage.
Engine Start-Up Mode
The ECM uses the intake air temperature sensor,
engine temperature sensor and the crankshaft po-
sition sensor (engine speed) inputs to determine
fuel injection quantity.
Normal Driving Modes
Engine idle, warm-up, acceleration, deceleration
and wide open throttle modes are controlled based
on all of the sensor inputs to the ECM. The ECM
uses these sensor inputs to adjust fuel quantity and
fuel injector timing. EGR valve control is performed
using feedback from the oxygen sensor. An oxygen
sensor is located in the exhaust manifold to sample
oxygen content exiting the engine cylinders. The
ECM uses the O2 sensor, along with other sensor
inputs, to govern the amount of exhaust gas recir-
culation to reduce HC (HydroCarbons) and CO
(Carbon Monoxide). Engine coolant is routed
through the base of the EGR valve to provide
additional cooling of the exhaust gas, which further
helps the reductions of emissions. The EGR valve
has a self-cleaning function. When the engine is
shut off, the EGR valve rotates twice to reduce
carbon deposits at the valve seat.
Overheat Production Mode
If the engine temperature is above 105ÉC (221ÉF)
and vehicle speed is above 40 km/h (25 MPH) the
ECM will limit fuel quantity for engine protection.
Limp-In Mode
The ECM utilizes different degrees of engine
limp-in. The ECM is able to limit engine rpm,
engine power output (turbo boost reduction), acti-
vate engine cooling fan or all of these functions
based on the type of fault that is detected. Critical
engine performance faults such as accelerator pedal
position sensor fault will result in a fixed idle speed
of approximately 680 rpm regardless of actual pedalposition. Other less critical faults will result in
power reduction throughout the full range of driv-
ing conditions.
Overspeed Detection Mode
If the ECM detects engine RPM that exceeds
5200 RPM, the ECM will set a DTC in memory,
limit engine RPM to no more than 2500 RPM, and
illuminate the MIL until the DTC is cleared.
After-Run Mode
The ECM transfers RAM information to ROM
and performs an Input/Output state check.
3.2.3 MONITORED CIRCUITS
The ECM is able to monitor and identify most
driveability related trouble conditions. Some cir-
cuits are directly monitored through ECM feedback
circuitry. In addition, the ECM monitors the voltage
state of some circuits and compares those states
with expected values. Other systems are monitored
indirectly when the ECM conducts a rationality test
to identify problems.
Although most subsystems of the engine control
module are either directly or indirectly monitored,
there may be occasions when diagnostic trouble
codes are not immediately identified. For a trouble
code to set, a specific set of conditions must occur
and unless these conditions occur, a DTC will not
set.
3.2.4 SKREEM OVERVIEW
The sentry key remote entry module system
(SKREEM) is designed to prevent unauthorized
vehicle operation. The system consists of a sentry
key remote entry module (SKREEM), ignition
key(s) equipped with a transponder chip and the
ECM. When the ignition switch is turned on, the
SKREEM interrogates the ignition key. If the igni-
tion key is Valid or Invalid, the SKREEM sends a
message to the ECM indicating ignition key status.
Upon receiving this message the ECM will termi-
nate engine operation or allow the engine to con-
tinue to operate.
3.2.5 SKREEM ON-BOARD DIAGNOSTICS
The SKREEM has been programmed to transmit
and monitor many different coded messages as well
as CAN Bus messages. This monitoring is called
On-Board Diagnostics. Certain criteria must be met
for a DTC to be entered into SKREEM memory. The
criteria may be a range of; input voltage, CAN Bus
message or coded messages to the SKREEM. If all
the criteria for monitoring a circuit or function are
met and a fault is detected, a DTC will be stored in
the SKREEM memory and the START ERROR indi-
cator will be turned on in the instrument cluster.
2
GENERAL INFORMATION

ohmmeter
voltmeter
jumper wires and probes
oscilloscope
6.0 GLOSSARY OF TERMS
A/Cair conditioning
APPaccelerator pedal position (sensor)
BCMbody control module
BPboost pressure (sensor)
CKPcrankshaft position (sensor)
CMPcamshaft position (sensor)
CTMcentral timer module
DLCdata link connector
ECMengine control module
ECTengine coolant temperature (sensor)
EGRexhaust gas recirculation (solenoid/
valve)
EOSengine oil sensor
IATintake air temperature (sensor)
IPintake pressure sensorMAFmass air flow (sensor)
MILmalfunction indicator lamp
msmillisecond(s)
O2oxygen sensor
PDCpower distribution center
S/Cspeed control
SKREEMsentry key remote entry module
SRCsignal range check
WIFwater in fuel (sensor)
10
GENERAL INFORMATION

ELECTRONIC CONTROL MODULES
TABLE OF CONTENTS
page page
CENTRAL TIMER MODULE
DESCRIPTION..........................1
OPERATION............................1
DIAGNOSIS AND TESTING - CENTRAL TIMER
MODULE.............................2
REMOVAL.............................2
INSTALLATION..........................3
CONTROLLER ANTILOCK BRAKE
DESCRIPTION..........................3
REMOVAL.............................3INSTALLATION..........................3
ENGINE CONTROL MODULE
DESCRIPTION..........................3
REMOVAL.............................6
INSTALLATION..........................6
TRANSMISSION CONTROL MODULE
DESCRIPTION..........................6
OPERATION............................7
STANDARD PROCEDURE - TCM ADAPTATION . 10
CENTRAL TIMER MODULE
DESCRIPTION
The central timer module (CTM) is located beneath
the driver seat. The CTM uses information carried on
the programmable communications interface (PCI)
data bus network along with many hard wired inputs
to monitor many sensor and switch inputs. In
response to those inputs, the circuitry and program-
ming of the CTM allow it to supply the vehicle occu-
pants with audible and visual information, and to
control and integrate many functions and features of
the vehicle through both hard wired outputs and the
transmission of message outputs to other modules in
the vehicle over the PCI data bus.
The features that the CTM supports or controls
include the following:
²Central Locking- The CTM on vehicles
equipped with the optional Vehicle Theft Security
System (VTSS) includes a central locking/unlocking
feature.
²Enhanced Accident Response- The CTM pro-
vides an optional enhanced accident response fea-
ture. This is a programmable feature.
²Panic Mode- The CTM provides support for
the optional RKE system panic mode including horn,
headlamp, and park lamp flash features.
²Power Lock Control- The CTM provides the
optional power lock system features, including sup-
port for the automatic door lock and door lock inhibit
modes.
²Programmable Features- The CTM provides
support for certain programmable features.
²Remote Keyless Entry- The CTM provides
the optional Remote Keyless Entry (RKE) system fea-
tures, including support for the RKE Lock (with
optional horn and park lamps flash), Unlock (with
park lamps flash, driver-door-only unlock, andunlock-all-doors), Panic, and illuminated entry
modes, as well as the ability to be programmed to
recognize up to four RKE transmitters. The RKE
horn, driver-door-only unlock, and unlock-all-doors
features are programmable.
²Vehicle Theft Security System- The CTM
provides control of the optional Vehicle Theft Secu-
rity System (VTSS) features, including support for
the central locking/unlocking mode and control of the
Security indicator in the instrument cluster.
Hard wired circuitry connects the CTM to the elec-
trical system of the vehicle. Refer to the appropriate
wiring information.
Many of the features in the vehicle controlled or
supported by the CTM are programmable using the
DRBIIItscan tool. However, if any of the CTM hard-
ware components are damaged or faulty, the entire
CTM unit must be replaced. The hard wired inputs
or outputs of all CTM versions can be diagnosed
using conventional diagnostic tools and methods;
however, for diagnosis of the CTM or the PCI data
bus, the use of a DRBIIItscan tool is required. Refer
to the appropriate diagnostic information.
OPERATION
The central timer module (CTM) monitors many
hard wired switch and sensor inputs as well as those
resources it shares with other modules in the vehicle
through its communication over the programmable
communications interface (PCI) data bus network.
The internal programming and all of these inputs
allow the CTM to determine the tasks it needs to
perform and their priorities, as well as both the stan-
dard and optional features that it should provide.
The CTM then performs those tasks and provides
those features through both PCI data bus communi-
cation with other modules and hard wired outputs
through a number of driver circuits, relays, and
VAELECTRONIC CONTROL MODULES 8E - 1

INSTRUMENT CLUSTER
DESCRIPTION
The instrument cluster for this model is an Elec-
troMechanical Instrument Cluster (EMIC) that is
located above the steering column opening in the
instrument panel, directly in front of the driver (Fig.
1). The remainder of the EMIC, including the mounts
and the electrical connections, are concealed within
the instrument panel behind the cluster bezel and
beneath the instrument panel top cover for the clus-
ter. The instrument cluster includes analog gauges,
meters, indicators, and acoustic signal transmit-
ters.The EMIC module also incorporates a multi-func-
tion indicator that consists of a digital Liquid Crystal
Display (LCD) unit for displaying odometer/trip
odometer information, an electronic digital clock,
engine oil level information, automatic transmission
gear selector position (PRNDL), and certain diagnos-
tic information. The multi-function indicator also has
four push button switches, which provide the vehicle
operator with an interface to adjust certain inputs to
the instrument cluster and to select from multiple
display options. If the vehicle is equipped with the
appropriate options, the multi-function indicator also
provides an outside ambient temperature indicator
display and an Active Service SYStem (ASSYST)
engine oil maintenance indicator to display engine oil
level and maintenance reminders.
The EMIC gauges and indicators are visible
through a dedicated opening in the cluster bezel on
the instrument panel and are protected by a clear
plastic cluster lens (Fig. 2) that is secured by eight
integral latches to the molded black plastic cluster
hood. Four, black plastic multi-function indicator
switch push buttons protrude through dedicated
holes in a rectangular black plastic switch bezel that
is integral to the cluster lens and located near the
lower edge of the cluster directly below the multi-
function indicator LCD unit. The cluster hood serves
as a visor and shields the face of the cluster from
ambient light and reflections to reduce glare. The
cluster hood has eight integral latches that engage
eight integral latch tabs on the cluster rear cover,
sandwiching the cluster housing unit between the
hood and the rear cover. The cluster hood also has
two integral pivot loops molded into its underside
that engage two pairs of molded pivot hooks that are
integral to the top of the instrument panel base
structure. These pivots allow the cluster to be rolled
rearward to ease service access to the wire harness
connectors at the back of the cluster.
The rear of the cluster housing and the EMIC elec-
tronic circuitry are protected by the molded plastic
rear cover. A mounting ear at each upper corner of
the rear cover are used to secure the EMIC to the
molded plastic instrument panel base unit with two
screws. The rear cover includes clearance holes for
the two cluster connector receptacles on the cluster
electronic circuit board. The connector receptacles on
the back of the cluster electronic circuit board con-
nect the EMIC to the vehicle electrical system
through two take outs with connectors from the vehi-
cle wire harness. The EMIC rear cover includes a
molded mounting tab and a latch feature that
secures the Remote Keyless Entry (RKE)/immobilizer
module to the back of the cluster. The RKE/immobi-
lizer module is connected to the vehicle electrical sys-
tem through a separate take out and connector of the
vehicle wire harness.
Fig. 1 Instrument Cluster
1 - COVER
2 - BEZEL
3 - INSTRUMENT CLUSTER
4 - STEERING WHEEL
5 - MULTI-FUNCTION SWITCH
6 - SPEED CONTROL SWITCH
Fig. 2 Instrument Cluster Components
1 - LENS
2 - HOOD
3 - CLUSTER HOUSING
4 - REAR COVER
8J - 2 INSTRUMENT CLUSTERVA

(6) Depress the release (Arrow A) and lift the lever
arm (Arrow B) to disconnect each of the two frame
wire harness connectors for the cluster from the con-
nector receptacles on the back of the cluster housing
(Fig. 6).
(7) Lift the instrument cluster upward far enough
to disengage the two molded plastic pivot loops inte-
gral to the base of the cluster hood from the two
pairs of molded plastic pivot hooks that are integral
to the top of the instrument panel base structure.
(8) Remove the instrument cluster from the instru-
ment panel.
INSTALLATION
WARNING: To avoid personal injury or death, on
vehicles equipped with airbags, disable the supple-
mental restraint system before attempting any
steering wheel, steering column, airbag, seat belt
tensioner, or instrument panel component diagno-
sis or service. Disconnect and isolate the battery
negative (ground) cable, then wait two minutes for
the system capacitor to discharge before perform-
ing further diagnosis or service. This is the only
sure way to disable the supplemental restraint sys-
tem. Failure to take the proper precautions could
result in accidental airbag deployment.
(1) Position the instrument cluster to the instru-
ment panel.
(2) Align the two molded plastic pivot loops inte-
gral to the base of the cluster hood between the twopairs of molded plastic pivot hooks that are integral
to the top of instrument panel base structure, then
push downward on the top of the cluster until the
loops snap into engagement with the hooks (Fig. 6).
(3) Roll the top of the instrument cluster rearward
to access, reconnect, and latch the two frame wire
harness connectors for the cluster to the connector
receptacles on the back of the cluster housing.
(4) Engage and latch the Remote Keyless Entry
(RKE)/immobilizer module to the back of the instru-
ment cluster rear cover (Fig. 5)
(5) Roll the top of the instrument cluster forward
to position the instrument cluster into the instru-
ment panel.
(6) Install and tighten the two screws that secure
the instrument cluster mounting ears to the instru-
ment panel base structure (Fig. 4). Tighten the
screws to 2 N´m (20 in. lbs.).
(7) Reinstall the cluster top cover onto the instru-
ment panel. (Refer to 23 - BODY/INSTRUMENT
PANEL/TOP COVER - CLUSTER - INSTALLA-
TION).
(8) Reinstall the cluster bezel onto the instrument
panel. (Refer to 23 - BODY/INSTRUMENT PANEL/
CLUSTER BEZEL - INSTALLATION).
(9) Reconnect the battery negative cable.
CAUTION: If an ineffective and unresponsive Instru-
ment Cluster (IC) has been replaced with a new
unit, the new IC must be initialized and configured
for certain optional equipment on the vehicle using
a cluster programming procedure. (Refer to 8 -
ELECTRICAL/INSTRUMENT CLUSTER - STANDARD
PROCEDURE - CLUSTER PROGRAMMING). Failure
to correctly perform this programming procedure
(also referred to as parameterization) prior to the IC
being electronically locked down will result in the
IC being incorrectly and irreversibly configured for
improper vehicle equipment options, which will
require the IC be replaced again with another new
and unused unit to resolve.
ABS INDICATOR
DESCRIPTION
An Anti-lock Brake System (ABS) indicator is stan-
dard equipment on all instrument clusters. The ABS
indicator is located near the lower edge of the instru-
ment cluster, to the right of the multi-function indi-
cator display. The ABS indicator consists of the
International Control and Display Symbol icon for
ªFailure of Anti-lock Braking Systemº imprinted
within a rectangular cutout in the opaque layer of
the instrument cluster overlay. The dark outer layer
of the overlay prevents the indicator from being
clearly visible when it is not illuminated. An amber
Fig. 6 Cluster Connectors
1 - STEERING WHEEL
2 - INSTRUMENT CLUSTER
3 - CONNECTOR (2)
VAINSTRUMENT CLUSTER 8J - 9

LAMPS / LIGHTING - INTERIOR
TABLE OF CONTENTS
page page
LAMPS/LIGHTING - INTERIOR
DESCRIPTION.........................28
OPERATION...........................29
SPECIFICATIONS - INTERIOR LIGHTING.....29
ASH RECEIVER/CIGAR LIGHTER LAMP UNIT
REMOVAL.............................30
INSTALLATION.........................30
CARGO/DOME LAMP BULB
REMOVAL.............................30
INSTALLATION.........................30
CARGO/DOME LAMP UNIT
REMOVAL.............................31
INSTALLATION.........................31
CARGO LAMP SWITCH
REMOVAL
REMOVAL - INSTRUMENT PANEL........31
REMOVAL - BULKHEAD................31
REMOVAL - REAR PILLAR..............31
INSTALLATION
INSTALLATION - INSTRUMENT PANEL.....32
INSTALLATION - BULKHEAD.............32
INSTALLATION - REAR PILLAR...........32
DOME/READING LAMP BULB
REMOVAL.............................32INSTALLATION.........................32
DOME/READING LAMP UNIT
REMOVAL.............................32
INSTALLATION.........................33
DOME LAMP/INTRUSION SENSOR BULB
REMOVAL.............................33
INSTALLATION.........................33
DOME LAMP/INTRUSION SENSOR
REMOVAL.............................33
INSTALLATION.........................34
DOOR JAMB SWITCH
REMOVAL.............................34
INSTALLATION.........................34
ENTRY/EXIT LAMP BULB
REMOVAL.............................34
INSTALLATION.........................35
ENTRY/EXIT LAMP UNIT
REMOVAL.............................35
INSTALLATION.........................35
TIME DELAY RELAY
REMOVAL.............................35
INSTALLATION.........................36
LAMPS / LIGHTING - INTERIOR
DESCRIPTION
The interior lighting for this model includes the
following standard and optional incandescent interior
lamps and controls:
²Ash Receiver/Cigar Lighter Lamp- An avail-
able ash receiver/cigar lighter lamp is secured by an
integral mount to the outside of the cigar lighter halo
ring. A single lamp serves to illuminate both the
translucent halo ring and the ash receiver.
²Cargo/Dome Lamp- Several cargo/dome lamp
units located overhead in both the front and rear of
the vehicle interior are standard equipment. These
lamps feature a single incandescent bulb. An optional
version of these lamps includes an integral three-po-
sition switch that protrudes through the lamp lens.
²Cargo Lamp Switch- Toggle-type remote
cargo lamp switches located in the accessory switch
bezel in the center of the instrument panel, on the
back side of the cargo compartment bulkhead panel,
and on the rear cargo door pillar are an available
option on all van models. The instrument panel
switch has two Light-Emitting Diode (LED) units,one for illumination and a second that provides an
indication. The switches mounted in the cargo com-
partment also have two LED units, but only the indi-
cation LED unit is functional in this application.
²Dome/Reading Lamp- An optional equipment
dome/reading lamp unit is located in the windshield
header area between the driver and passenger sun
visors. This lamp features two incandescent bulbs,
one dome lamp bulb and a second, dedicated reading
lamp bulb. An integral four-position switch protrudes
through the lamp lens.
²Dome Lamp/Intrusion Sensor- An optional
equipment dome lamp/intrusion sensor unit is
located overhead in the vehicle interior. This lamp
features four incandescent bulbs, two for dome lamps
and two for dedicated right and left reading lamps.
This lamp has two integral three-position switches,
one to control interior lamp operation and one to con-
trol reading lamp operation. This lamp also houses
three intrusion sensors that are part of an optional
vehicle theft security system.
²Door Jamb Switch- A door jamb switch for
each front door is standard equipment on all models.
A door jamb switch for each sliding side door and the
8L - 28 LAMPS/LIGHTING - INTERIORVA

right rear door is standard equipment on wagon mod-
els. The sliding and rear door jamb switches are not
available for van models.
²Entry/Exit Lamp- An entry/exit lamp to illu-
minate each front and sliding side door step well is
optional equipment on wagon models.
²Time Delay Relay- Vehicles equipped with the
optional remote cargo lamp switches also have a time
delay relay located in the electrical center within the
driver side front seat riser.
Hard wired circuitry connects the interior lighting
system components to the electrical system of the
vehicle. These hard wired circuits are integral to sev-
eral wire harnesses, which are routed throughout the
vehicle and retained by many different methods.
These circuits may be connected to each other, to the
vehicle electrical system and to the interior lighting
system components through the use of a combination
of soldered splices, splice block connectors, and many
different types of wire harness terminal connectors
and insulators. Refer to the appropriate wiring infor-
mation. The wiring information includes wiring dia-
grams, proper wire and connector repair procedures,
further details on wire harness routing and reten-
tion, as well as pin-out and location views for the
various wire harness connectors, splices and grounds.
OPERATION
The interior lighting systems can be divided into
two general classifications based upon the circuit
that controls their operation: The interior lighting
circuit, or the exterior lighting circuit. The hard
wired circuits and components of the interior lighting
systems may be diagnosed and tested using conven-
tional diagnostic tools and procedures.
INTERIOR LIGHTING CIRCUIT
Depending upon the vehicle model (van or wagon)
and the selected vehicle options the interior lighting
circuit may include dome/cargo lamps located over-
head in the front and rear of the vehicle, a dome/
reading lamp located in the header area above the
windshield between the sun visors, and entry/exit
lamps located in the front and sliding side door step
wells.
WAGON MODELS
In all wagon models, the lamps in the interior
lighting circuit are provided with battery current at
all times by a fuse in the fuse block beneath the
steering column. The front, side, and rear door jamb
switches control a ground path for each of these
lamps, except for the optional reading lamp. If the
lamp has an optional integral switch, that switch has
three separate positions. The first position provides a
ground path independent of the door jamb switches
to turn the lamp On. The second, or center position
allows the door jamb switches to control the lamp.The third position segregates that lamp from the
door jamb switch input, turning the lamp Off. In the
case of the optional dome/reading lamp, the integral
lamp switch has a fourth position which will illumi-
nate only the reading lamp bulb.
VAN MODELS
Unless a van model is equipped with an optional
remote cargo lamp switch, all of the lamps in the
interior lighting circuit operate the same way as the
wagon models except that there are only two door
jamb switches, one for each front door. If the vehicle
is equipped with an optional remote cargo lamp
switch, the lamps in the rear of the vehicle on the
interior lighting circuit are provided with battery
current by the time delay relay. The time delay relay
is a smart relay containing active electronic elements
that comprise an electronic timer logic circuit. When
the remote cargo lamp switches provide the proper
input to the time delay relay, the relay logic responds
by energizing the relay control coil. The energized
relay control coil provides battery current to all of
the lamps on the rear interior lighting circuit and to
the indicator Light-Emitting Diode (LED) units in
the remote cargo switches causing each to illuminate.
If a remote cargo lamp switch remains On for more
than about fifteen minutes, the time delay relay will
then automatically de-energize the rear interior
lighting circuits until the remote cargo lamp switch
is cycled Off and then back On.
EXTERIOR LIGHTING CIRCUIT
The exterior lighting circuit provides battery cur-
rent to the optional ash receiver/cigar lighter lamp
and to the illumination Light-Emitting Diode (LED)
unit within the remote cargo lamp switch in the
instrument panel accessory switch bezel whenever
the exterior lamps are turned On.
SPECIFICATIONS - INTERIOR LIGHTING
VALAMPS/LIGHTING - INTERIOR 8L - 29

Communication Interface (SCI) data bus line for sup-
plemental restraint system programming or diagno-
sis and testing through the 16-way Data Link
Connector (DLC) located on the dash panel below the
driver side end of the instrument panel. A hard wired
output from the ACM is used for control of the airbag
indicator in the ElectroMechanical Instrument Clus-
ter (EMIC). (Refer to 8 - ELECTRICAL/INSTRU-
MENT CLUSTER/AIRBAG INDICATOR -
OPERATION).
The ACM microprocessor continuously monitors all
of the supplemental restraint system electrical cir-
cuits to determine the system readiness. If the ACM
detects a monitored system fault, it sets an appropri-
ate Diagnostic Trouble Code (DTC) and sends an out-
put to the EMIC to turn on the airbag indicator. The
ACM illuminates the indicator for about four seconds
each time the ignition switch is turned to the On
position as a bulb test. If the indicator remains illu-
minated for about ten seconds after the ignition
switch is turned to the On position, the ACM has
detected a non-critical fault that poses no danger to
the vehicle occupants. If the airbag indicator illumi-
nates solid (not flashing) while driving or stays on
longer than ten seconds following the bulb test, the
ACM has detected a critical fault that may cause the
airbags not to deploy when required or to deploy
when not required. An active fault only remains for
the duration of the fault, or in some cases, for the
duration of the current ignition switch cycle, while a
stored fault causes a DTC to be stored in memory by
the ACM.
The ACM receives battery current through a fused
ignition switch output circuit. The ACM receives
ground through a ground circuit and take out of the
vehicle wire harness. This take out has an eyelet ter-
minal connector secured by a nut to a ground stud on
the floor panel directly below the ACM within the
driver side seat riser. A case ground is also provided
for the ACM through a ground circuit and eyelet ter-
minal connector secured under the left rear ACM
mounting screw. These connections allow the ACM to
be operational whenever the ignition switch is in the
On position.
The ACM also contains an energy-storage capaci-
tor. When the ignition switch is in the On position,
this capacitor is continually being charged with
enough electrical energy to deploy the supplemental
restraint components for up to one second following a
battery disconnect or failure. The purpose of the
capacitor is to provide backup supplemental restraint
system protection in case there is a loss of battery
current supply to the ACM during an impact.
Two sensors are contained within the ACM, an
electronic impact sensor and a safing sensor. These
electronic sensors are accelerometers that sense the
rate of vehicle deceleration, which provide verifica-
tion of the direction and severity of an impact. Onmodels equipped with optional side curtain airbags,
the ACM also monitors inputs from two remote side
impact sensors located within the left and right front
door step wells to control deployment of the side cur-
tain airbag units.
The safing sensor is an electronic accelerometer
sensor within the ACM that provides an additional
logic input to the ACM microprocessor. The safing
sensor is used to verify the need for a supplemental
restraint deployment by detecting impact energy of a
lesser magnitude than that of the primary electronic
impact sensors, and must exceed a safing threshold
in order for the airbags to deploy. Vehicles equipped
with optional side curtain airbags feature a second
safing sensor within the ACM to provide confirma-
tion to the ACM microprocessor of side impact forces.
This second safing sensor is a bi-directional unit that
detects impact forces from either side of the vehicle.
Pre-programmed decision algorithms in the ACM
microprocessor determine when the deceleration rate
as signaled by the impact sensors and the safing sen-
sors indicate an impact that is severe enough to
require supplemental restraint system protection.
When the programmed conditions are met, the ACM
sends the proper electrical signals to deploy the front
airbags and seat belt tensioners and, if the vehicle is
so equipped, either side curtain airbag unit.
The ACM also provides a hard wired electrical
crash signal output following a supplemental
restraint deployment event. This output is used to
signal other electronic modules in the vehicle to pro-
vide their enhanced accident response features,
which include automatically disabling the engine
from running and unlocking all of the doors. How-
ever, these responses are each dependent upon the
circuits, components, and modules controlling these
features remaining intact from collateral damage
incurred during the vehicle impact.
A single ACM is used for all variations of the sup-
plemental restraint system available in this vehicle.
This ACM is programmable and in order to function
properly it must be programmed for the correct vehi-
cle supplemental restraint system equipment using
an initialization procedure. The initialization proce-
dure requires the use of a diagnostic scan tool. Refer
to the appropriate diagnostic information. The hard
wired inputs and outputs for the ACM may be diag-
nosed and tested using conventional diagnostic tools
and procedures. However, conventional diagnostic
methods will not prove conclusive in the diagnosis of
the ACM or the supplemental restraint system. The
most reliable, efficient, and accurate means to diag-
nose the ACM or the supplemental restraint system
requires the use of a diagnostic scan tool. Refer to
the appropriate diagnostic information.
VARESTRAINTS 8O - 9