Chrysler RAM TRUCK 2500 1994 Service Manual page 983

14 - 42 FUEL SYSTEM
Fig. 21 02S Location—8.0L/5.9L HDC Engine-
Typical
DATA LINK CONNECTOR—PCM PIN #25—PCM
OUTPUT
The data link connector (diagnostic scan tool con­
nector) links the Diagnostic Readout Box (DRB) scan
tool or the Mopar Diagnostic System (MDS) with the
powertrain control module (PCM). The data link con­
nector is located i n the engine compartment (Fig. 22).
For operation of the DRB scan tool, refer to the ap­
propriate Powertrain Diagnostic Procedures service
manual.
The data link connector uses two different pins on
the PCM. Pin #25 is for Data Link Transmit and pin
#45 is for Data Link Receive.
P O W E R T R A I N C O N T R O L
M O D U L E (PCM) J9414-11
Fig. 22 PCM and Data Link Connector—Typical
CCD BUS(+)—PCM PIN #26—PCM OUTPUT
Various modules exchange information through a
communications port called the CCD BUS(+).
•
AIR CONDITIONING (A/C) CONTROLS—PCM PINS
#27 AND #28—PCM INPUT
The A/C control system information applies to fac­
tory installed air conditioning units.
A/C BEQUEST SIGNAL? Once A/C has been se­
lected, the powertrain control module (PCM) receives
the A/C request signal from the evaporator switch.
The input indicates that the evaporator temperature
is i n the proper range for A/C application. The PCM
uses this input to cycle the A/C compressor clutch
(through the A/C relay). I t will also determine the
correct engine idle speed through the idle air control
(IAC) motor position.
I f the A/C low-pressure switch opens (indicating a
low refrigerant level), the PCM will not receive an
A/C select signal. The PCM will then remove the
ground from the A/C relay. This will deactivate the
A/C compressor clutch.
I f the evaporator switch opens, (indicating that
evaporator is not i n proper temperature range), the
PCM will not receive the A/C request signal. The
PCM will then remove the ground from the A/C relay,
deactivating the A/C compressor clutch.
BRAKE SWITCH—PCM PIN #29—PCM INPUT
When the brake light switch is activated, the pow­
ertrain control module (PCM) receives an input indi­
cating that the brakes are being applied. After
receiving this input, the PCM maintains idle speed to
a scheduled rpm through control of the idle air con­
trol (IAC) motor. The brake switch input is also used
to control the speed control system and electrical op­
eration of the transmission torque converter.
PARK/NEUTRAL SWITCH—PCM PIN #30—PCM
INPUT
The park/neutral switch provides an input to the
powertrain control module (PCM). This will indicate
that the automatic transmission is i n Park, Neutral
or a Drive gear selection. This input is used to deter­
mine idle speed (varying with gear selection), fuel in­
jector pulse width and ignition timing advance. Refer
to Group 21, Transmissions, for testing, replacement
and adjustment information.
TRANSMISSION TEMPERATURE WARNING
LAMP—PCM PIN #31—PCM OUTPUT
9.M/5.21/5.9L ENGINES—AUTOMATIC
TRANSMISSIONS ONLY
An instrument panel mounted lamp (Fig. 23) is
used to warn of a possible transmission overheating
condition. When transmission temperature has been
determined to be above approximately 280 degrees F
by the transmission temperature sensor, a signal is
sent to the powertrain control module (PCM). The
PCM will then control warning lamp operation. The