Jeep Cherokee 2000, Service Manual

Page: 854 / 1528

perature, throttle position, transmission gear selec-
tion (automatic transmission), vehicle speed, power
steering pump pressure (2.5L engine only), and the
brake switch.
The PCM adjusts idle speed based on inputs it
receives from sensors that react to: throttle position,
vehicle speed, transmission gear selection, engine
coolant temperature and from inputs it receives from
the air conditioning clutch switch and brake switch.
Based on inputs that it receives, the PCM adjusts
ignition coil dwell. The PCM also adjusts the gener-
ator charge rate through control of the generator
field and provides speed control operation.
NOTE: PCM Inputs:
•
A/C request (if equipped with factory A/C)
•
A/C select (if equipped with factory A/C)
•
Auto shutdown (ASD) sense
•
Battery temperature
•
Battery voltage
•
Brake switch
•
CCD bus (+) circuits
•
CCD bus (-) circuits
•
Camshaft position sensor signal
•
Crankshaft position sensor
•
Data link connection for DRB scan tool
•
Engine coolant temperature sensor
•
Extended idle switch (4.0L engine with police
package)
•
Fuel level
•
Generator (battery voltage) output
•
Ignition circuit sense (ignition switch in on/off/
crank/run position)
•
Intake manifold air temperature sensor
•
Leak detection pump (switch) sense (if equipped)
•
Manifold absolute pressure (MAP) sensor
•
Oil pressure
•
Oxygen sensors
•
Park/neutral switch (auto. trans. only)
•
Power ground
•
Power steering pressure switch (2.5L engine
only)
•
Sensor return
•
Signal ground
•
Speed control multiplexed single wire input
•
Throttle position sensor
•
Vehicle speed sensor
NOTE: PCM Outputs:
•
A/C clutch relay
•
Auto shutdown (ASD) relay
•
CCD bus (+/-) circuits for: speedometer, voltme-
ter, fuel gauge, oil pressure gauge/lamp, engine temp.
gauge and speed control warn. lamp
•
Data link connection for DRB scan tool
•
EGR valve control solenoid (if equipped)
•
EVAP canister purge solenoid
•
Five volt sensor supply (primary)
•
Five volt sensor supply (secondary)
•
Fuel injectors
•
Fuel pump relay
•
Generator field driver (-)
•
Generator field driver (+)
•
Idle air control (IAC) motor
•
Ignition coil
•
Leak detection pump (if equipped)
•
Malfunction indicator lamp (Check engine lamp).
Driven through CCD circuits.
•
Radiator cooling fan relay
•
Speed control vacuum solenoid
•
Speed control vent solenoid
•
Tachometer (if equipped). Driven through CCD
circuits.
•
Transmission convertor clutch circuit
MODES OF OPERATION
OPERATION
As input signals to the Powertrain Control Module
(PCM) change, the PCM adjusts its response to the
output devices. For example, the PCM must calculate
different injector pulse width and ignition timing for
idle than it does for wide open throttle (WOT).
The PCM will operate in two different modes:
Open Loop and Closed Loop.
During Open Loop modes, the PCM receives input
signals and responds only according to preset PCM
programming. Input from the oxygen (O2S) sensors
is not monitored during Open Loop modes.
During Closed Loop modes, the PCM will monitor
the oxygen (O2S) sensors input. This input indicates
Fig. 1 PCM Location
1 – (3) 32–WAY CONNECTORS
2 – PCM
14 - 26 FUEL SYSTEM
XJ
DESCRIPTION AND OPERATION (Continued)