Ccd Bus (+/-) Circuits-Pcm Outputs; Data Link Connector-Pcm Input And Output; Description And Operation; Fuel Injectors-Pcm Output - Jeep cherokee 2000 Service Manual

XJ
DESCRIPTION AND OPERATION (Continued)
• the ignition key is left in the ON position. This
is if the engine has not been running for approxi-
mately 1.8 seconds.
• there is a crankshaft position sensor signal to
the PCM that is lower than pre-determined values.
The PCM will sense if or when the ASD relay has
been activated through a "sense circuit". Refer to
Automatic Shut-Down (ASD) Relay Sense-PCM Input
for additional information.

CCD BUS (+/-) CIRCUITS-PCM OUTPUTS

OPERATION
The Powertrain Control Module (PCM) sends cer-
tain output signals through the CCD bus circuits.
These signals are used to control certain instrument
panel located items and to determine certain identi-
fication numbers.
Refer to Group 8E, Instrument Panel and Gauges
for additional information.
DATA LINK CONNECTOR—PCM INPUT AND
OUTPUT
DESCRIPTION
The data link connector is located at the lower
edge of the instrument panel near the steering col-
umn.
OPERATION
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).
FUEL INJECTORS—PCM OUTPUT
DESCRIPTION
The fuel injectors are connected to the engine with
the fuel injector rail.
OPERATION
The nozzle ends of the injectors are positioned into
openings in the intake manifold just above the intake
valve ports of the cylinder head. The engine wiring
harness connector for each fuel injector is equipped
with an attached numerical tag (INJ 1, INJ 2 etc.).
This is used to identify each fuel injector with its
respective cylinder number.
The injectors are energized individually in a
sequential order by the Powertrain Control Module
(PCM). The PCM will adjust injector pulse width by
switching the ground path to each individual injector
on and off. Injector pulse width is the period of time
that the injector is energized. The PCM will adjust
injector pulse width based on various inputs it
receives.
Battery voltage (12 volts +) is supplied to the injec-
tors through the ASD relay. The ASD relay will shut-
down the 12 volt power source to the fuel injectors if
the PCM senses the ignition is on, but the engine is
not running. This occurs after the engine has not
been running for approximately 1.8 seconds.
The PCM determines injector on-time (pulse width)
based on various inputs.

FUEL PUMP RELAY-PCM OUTPUT

DESCRIPTION
The 5–pin, 12–volt, fuel pump relay is located in
the Power Distribution Center (PDC). Refer to the
label on the PDC cover for relay location.
OPERATION
The Powertrain Control Module (PCM) energizes
the electric fuel pump through the fuel pump relay.
The fuel pump relay is energized by first applying
battery voltage to it when the ignition key is turned
ON, and then applying a ground signal to the relay
from the PCM.
Whenever the ignition key is turned ON, the elec-
tric fuel pump will operate. But, the PCM will shut-
down the ground circuit to the fuel pump relay in
approximately 1–3 seconds unless the engine is oper-
ating or the starter motor is engaged.
IDLE AIR CONTROL (IAC) MOTOR—PCM
OUTPUT
DESCRIPTION
The IAC stepper motor is mounted to the throttle
body, and regulates the amount of air bypassing the
control of the throttle plate. As engine loads and
ambient temperatures change, engine rpm changes. A
pintle on the IAC stepper motor protrudes into a pas-
sage in the throttle body, controlling air flow through
the passage. The IAC is controlled by the Powertrain
Control Module (PCM) to maintain the target engine
idle speed.
OPERATION
At idle, engine speed can be increased by retract-
ing the IAC motor pintle and allowing more air to
pass through the port, or it can be decreased by
restricting the passage with the pintle and diminish-
ing the amount of air bypassing the throttle plate.
The IAC is called a stepper motor because it is
moved (rotated) in steps, or increments. Opening the
IAC opens an air passage around the throttle blade
which increases RPM.
FUEL SYSTEM 14 - 35