3.2.2
CAN BUS
The CAN bus (controller area network) is a data
bus system specifically design for inter module
communication on this vehicle. The CAN bus con-
sists of a special twisted two-core cable. Control
modules are connected to this
9twisted pair9. The
CAN bus incorporates two terminating resistors.
One terminator is built into the Engine Control
Module (ECM) and the other is built into the Sentry
Key Remote Entry Module (SKREEM). Each resis-
tor has a value of 120 ohms. The resistor condition
can be confirmed by disconnecting the control mod-
ule and measuring the resistance value at the
appropriate control module pins. This measure-
ment should read 120 ohms. The two CAN circuits,
CAN C Bus (+) and CAN C Bus (-), are bridged by
these two terminating resistors when all control
modules are connected to the bus. These two resis-
tors are connected to the CAN bus network in
parallel.
The
measurement
between
the
two
twisted CAN circuits, with both the ECM and
SKREEM connected, should measure a value of 60
ohms.
The CAN bus is bi-directional. This means that
each connected control module can send and receive
information. Transmission of data takes place re-
dundantly via both circuits. The data bus levels are
mirrored, meaning that if the binary level on one
circuit is 0, the other circuit transmits binary level
1 and vice versa. The two line concept is used for
two reasons: for fault identification and as a safety
concept.
If a voltage peak occurs on just one circuit, the
receivers can identify this as a fault and ignore the
voltage peak. If a short circuit or interruption
occurs on one of the two CAN circuits, a software-
hardware linked safety concept allows switching to
a single-line operation. The defective CAN circuit is
shut down. A specific data protocol controls how and
when the participants can send and receive.
NOTE: It is important to note the CAN Bus
circuits
are
used
for
inter-module
communication
only,
and
is
no
way
connected to the K-Lines.
The following modules that use the CAN Bus on
this vehicle are:
•
Automatic Temperature Control (ATC)
•
Controller Antilock Brake (CAB)
•
Engine Control Module (ECM)
•
Instrument Cluster (IC)
•
Sentry Key Remote Entry Module (SKREEM)
•
Shifter Assembly (SA)
•
Transmission Control Module (TCM)
3.3
HEATING & A/C SYSTEM
3.3.1
AUTOMATIC TEMPERATURE
CONTROL (ATC)
3.3.1.1
SYSTEM CONTROLS
The ATC Module:
•
is fully addressable with the DRBIII
t.
I
The DRBIII
t communicates with the ATC
Module through the Diagnostic Link Connector
(DLC) via a K-Line.
•
communicates with other modules over the Con-
troller Area Network (CAN) C Bus.
•
controls A/C clutch operation.
•
controls EBL operation.
•
controls water cycle valve operation.
I
The water cycle valve is a normally open valve,
meaning that it allows full engine coolant flow
through the heater core when no power is
delivered to the valve. The ATC controls the
valve with a pulse width signal. The lower the
percentage of the pulse width signal the more
the valve is open.
•
controls Residual Heat Utilization (REST) func-
tion.
•
controls blower motor operation, providing four
blower speeds (Low, M1, M2, & High).
•
controls recirculation air solenoid valve.
•
controls the mode door via cables.
•
controls the main power supply to the Heater
Booster (if equipped).
•
uses air inlet temperature sensor, air outlet tem-
perature sensor, and evaporator temperature
sensor input, as well as data from other modules
to maintain occupant comfort levels.
3.3.1.2
SYSTEM DIAGNOSTICS
Fault detection is through active and stored Diag-
nostic Trouble Codes (DTCs)
•
DTCs are displayed by the DRBIII
t.
•
Active DTCs are those which currently exist in
the system. The condition causing the fault must
be repaired in order to clear this type of DTC.
•
Stored DTCs are those which occurred in the
system since the ATC Module received the last
9clear diagnostic info9 message.
Testing Preparation & Diagnostics
Set the necessary system functions accordingly so
that all of the following prerequisites are met prior
to performing diagnostic tests on the ATC system:
5
GENERAL INFORMATION