Dodge ram truck 3500 1996 Service Manual page 1354

14 - 121
FUEL
SYSTEM
B R
D E S C R I P T I O N A N D O P E R A T I O N ( C o n t i n u e d )
illuminate the generator lamp (if equipped) on the
instrument panel. For example, during low idle with
all accessories turned on, the lamp may momentarily
go on. Refer to Groups 8A and 8C for charging sys­
tem information.
GENERATOR FIELD—PCM OUTPUT
The powertrain control module (PCM) regulates
the charging system voltage within a range of 12.9 to
15.0 volts. Refer to Groups 8A and 8C for charging
system information.
DATA LINK CONNECTOR—PCM INPUT AND
OUTPUT
The 16-way data link connector (diagnostic scan
tool connector) links the Diagnostic Readout Box
(DRB) scan tool or the Mopar Diagnostic System
(MDS) with the powertrain control module (PCM).
The data link connector (Fig. 14) is located at lower
edge of instrument panel near steering column. For
operation of the DRB scan tool, refer to the appropri­
ate Powertrain Diagnostic Procedures service man­
ual.
16-WAY DATA
LINK CONNECTOR
805dd852
Fig. 14 16-Way Data Link Connector
MALFUNCTION INDICATOR LAMP—PCM OUTPUT
The malfunction indicator lamp illuminates on the
instrument panel each time the ignition key is
turned on. This lamp is displayed on the instrument
panel as the CHECK ENGINE lamp (Fig. 15). Note
that the lamp will illuminate for approximately two
seconds each time the key is initially turned to the
ON position. This feature is used as a bulb check.
If the powertrain control module (PCM) receives an
incorrect signal, or no signal from certain sensors or
components, the lamp is turned on. This is a warning
that the PCM has recorded a system or sensor mal­
function. I t signals an immediate need for service.
The lamp can also be used to display a diagnostic
trouble code (DTC). Cycle the ignition switch On-Off-
Fig. 15 Check Engine Lamp—Typical Location
On-Off-On within three seconds and any codes stored
in the PCM memory will be displayed. This is done
in a series of flashes representing digits. Refer to On-
Board Diagnostics i n the General Diagnosis section
of this group for more information.
OVERDRIVE LAMP—PCM OUTPUT
This circuit controls a signal for the operation of
the instrument panel mounted push-button overdrive
lamp switch. When the lamp is illuminated, the over­
drive is disengaged.
OVERDRIVE/OVERRIDE SWITCH-PCM INPUT
On vehicles equipped with an automatic transmis­
sion and overdrive, the powertrain control module
(PCM) regulates the 3-4 overdrive up-shift and down­
shift through the overdrive solenoid. This solenoid is
located in the transmission. An overdrive/override
push-button switch is located on the instrument
panel.
The PCM circuit for overdrive is controlled by
inputs from the engine coolant temperature sensor
and vehicle speed sensor. I f coolant temperature and
vehicle speed are not within the preset PCM specifi­
cations, the PCM will not allow the transmission to
shift into overdrive. These preset PCM specifications
must be met before the push-button switch will be
allowed to control overdrive operation.
The overdrive/override push-button switch is nor­
mally closed (overdrive allowed) when the lamp is
not illuminated. I t opens (overdrive not allowed)
when the operator presses the switch and the lamp is
illuminated. The switch will revert to its normally
closed position (lamp off) each time the ignition
switch in turned on. The transmission downshifts i f
the operator presses the override switch while in
overdrive.
Refer to Group 21 for more transmission informa­
tion.