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8M - 6
MESSAGE SYSTEMS
AMBIENT TEMP SENSOR (Continued)
Fig. 6 Ambient Temperature Sensor
repaired and, if faulty or damaged, it must be
replaced.
OPERATION
The ambient temperature sensor is a variable
resistor. A five-volt reference signal is sent to the sen-
sor by the Front Control Module. The front control
module monitors the return signal voltage on a ded-
icated temperature sensor signal circuit. Based upon
the resistance in the sensor, the Front Control Mod-
ule is programmed to correspond to a specific temper-
ature. The Front Control Module then sends the
proper ambient temperature messages over the PCI
data bus circuit.
The HVAC temperature display function is sup-
ported by the ambient temperature sensor, a wiring
circuit, the Front Control Module and the Program-
mable Communications Interface (PCI) data bus. If
any portion of the ambient temperature sensor cir-
cuit fails, the Front Control Module should self-diag-
nose the circuit.
DIAGNOSIS AND TESTING - AMBIENT
TEMPERATURE SENSOR
(1) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Disconnect the ambient temperature sensor wire har-
ness connector. Refer to the removal procedure in
this section.
(2) Using an ohm meter, measure the resistance
through the ambient temperature sensor. At room
temperature (approx. 68°F), the sensor resistance
should be between 9-11 kilohms (9000 – 11000 ohms).
The sensor resistance should read between these two
values. If OK, the sensor is OK at this time. If not
OK, replace the faulty ambient temperature sensor.
REMOVAL
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the front grille assembly from the vehi-
cle. Refer to the Body section for the procedure.
(3) Disconnect the sensor electrical connector.
Depress the connector retaining tab and pull the con-
nector straight off the ambient temperature sensor.
(4) Remove the sensor retaining screw and remove
the sensor from the vehicle.
INSTALLATION
(1) Install the sensor and connect the sensor elec-
trical connector.
(2) Install the front grille assembly on the vehicle.
Refer to the Body section for the procedure.
(3) Connect the battery negative cable.
COMPASS MINI-TRIP
COMPUTER
DESCRIPTION
The Compass Mini-Trip Computer (CMTC) is a
module located in the overhead console. On CS vehi-
cle's the CMTC module display screen is located in
the instrument cluster.
The Compass Mini-Trip Computer module contains
a central processing unit and interfaces with other
electronic modules in the vehicle over the Program-
mable Communications Interface PCI data bus cir-
cuit.
The CMTC module uses its internal programming
and all of its data inputs to calculate the requested
data. This data includes the Tire Pressure Monitor-
ing, Compass information, Universal Transmitter,
Average Fuel Economy (AFE), Distance To Empty
(DTE) and Distance To Service (DTS).
The compass mini-trip computer module cannot be
repaired, and is available for service only as a unit.
This unit includes the plastic module. If the CMTC
module is faulty or damaged, the complete module
must be replaced.
OPERATION
The Compass Mini-Trip Computer is wired to both
non-switched and ignition switched sources of battery
current so that some of its features remain opera-
tional at any time, while others may only operate
with the ignition switch in the On position. Informa-
tion collected in the CMTC module is sent to the
instrument cluster display via the PCI data bus cir-
cuit.
The information collected or generated in the com-
pass mini-trip computer module includes tire pres-
sure monitoring, compass and universal transmitter
information.
CS
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