Jeep Liberty KJ. Manual — part 1486
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When engine has reached operating temperature, the PCM will begin monitoring O2S sensor input. The sys-
tem will then leave the warm-up mode and go into closed loop operation.
IDLE MODE
When the engine is at operating temperature, this is a Closed Loop mode. At idle speed, the PCM receives inputs
from:
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Air conditioning select signal (if equipped)
•
Air conditioning request signal (if equipped)
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Battery voltage
•
Engine Coolant Temperature (ECT) sensor
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CranKshaft Position (CKP) sensor
•
Intake manifold Air Temperature (IAT) sensor
•
Manifold Absolute Pressure (MAP) sensor
•
Throttle Position Sensor (TPS)
•
Camshaft position sensor signal
•
Battery voltage
•
Park/neutral switch (gear indicator signal—auto. trans. only)
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Oxygen sensors
Based on these inputs, the following occurs:
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Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control injection
sequence and injector pulse width by turning the ground circuit to each individual injector on and off.
•
The PCM monitors the O2S sensor input and adjusts air-fuel ratio by varying injector pulse width. It also
adjusts engine idle speed through the IAC motor.
•
The PCM adjusts ignition timing by increasing and decreasing spark advance.
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The PCM operates the A/C compressor clutch through the A/C compressor clutch relay. This is done if A/C has
been selected by the vehicle operator and specified pressures are met at the high and low–pressure A/C
switches. Refer to Heating and Air Conditioning for additional information.
CRUISE MODE
When the engine is at operating temperature, this is a Closed Loop mode. At cruising speed, the PCM receives
inputs from:
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Air conditioning select signal (if equipped)
•
Air conditioning request signal (if equipped)
•
Battery voltage
•
Engine Coolant Temperature (ECT) sensor
•
CranKshaft Position (CKP) sensor
•
Intake manifold Air Temperature (IAT) sensor
•
Manifold Absolute Pressure (MAP) sensor
•
Throttle Position Sensor (TPS)
•
Camshaft position sensor signal
•
Park/neutral switch (gear indicator signal -auto. trans. only)
•
Oxygen (O2S) sensors
Based on these inputs, the following occurs:
•
Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then adjust the injector
pulse width by turning the ground circuit to each individual injector on and off.
•
The PCM monitors the O2S sensor input and adjusts air-fuel ratio. It also adjusts engine idle speed through
the IAC motor.
•
The PCM adjusts ignition timing by turning the ground path to the coil(s) on and off.
•
The PCM operates the A/C compressor clutch through the clutch relay. This happens if A/C has been selected
by the vehicle operator and requested by the A/C thermostat.
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ELECTRONIC CONTROL MODULES
KJ
ACCELERATION MODE
This is an Open Loop mode. The PCM recognizes an abrupt increase in throttle position or MAP pressure as a
demand for increased engine output and vehicle acceleration. The PCM increases injector pulse width in response
to increased throttle opening.
DECELERATION MODE
When the engine is at operating temperature, this is an Open Loop mode. During hard deceleration, the PCM
receives the following inputs.
•
Air conditioning select signal (if equipped)
•
Air conditioning request signal (if equipped)
•
Battery voltage
•
Engine Coolant Temperature (ECT) sensor
•
CranKshaft Position (CKP) sensor
•
Intake manifold Air Temperature (IAT) sensor
•
Manifold Absolute Pressure (MAP) sensor
•
Throttle Position Sensor (TPS)
•
Camshaft position sensor signal
•
Park/neutral switch (gear indicator signal—auto. trans. only)
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Vehicle speed
If the vehicle is under hard deceleration with the proper rpm and closed throttle conditions, the PCM will ignore the
oxygen sensor input signal. The PCM will enter a fuel cut-off strategy in which it will not supply a ground to the
injectors. If a hard deceleration does not exist, the PCM will determine the proper injector pulse width and continue
injection.
Based on the above inputs, the PCM will adjust engine idle speed through the IAC motor.
The PCM adjusts ignition timing by turning the ground path to the coil on and off.
WIDE OPEN THROTTLE MODE
This is an Open Loop mode. During wide open throttle operation, the PCM receives the following inputs.
•
Battery voltage
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Engine Coolant Temperature (ECT) sensor
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CranKshaft Position (CKP) sensor
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Intake manifold Air Temperature (IAT) sensor
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Manifold Absolute Pressure (MAP) sensor
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Throttle Position Sensor (TPS)
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Camshaft position sensor signal
During wide open throttle conditions, the following occurs:
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Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control the injection
sequence and injector pulse width by turning the ground circuit to each individual injector on and off. The PCM
ignores the oxygen sensor input signal and provides a predetermined amount of additional fuel. This is done
by adjusting injector pulse width.
•
The PCM adjusts ignition timing by turning the ground path to the coil(s) on and off.
IGNITION SWITCH OFF MODE
When ignition switch is turned to OFF position, the PCM stops operating the injectors, ignition coil, ASD relay and
fuel pump relay.
5 VOLT SUPPLIES
Two different Powertrain Control Module (PCM) five volt supply circuits are used; primary and secondary.
IGNITION CIRCUIT SENSE
This circuit ties the ignition switch to the Powertrain Control Module (PCM).
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ELECTRONIC CONTROL MODULES
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POWER GROUNDS
The Powertrain Control Module (PCM) has two main grounds. Both of these grounds are referred to as power
grounds. All of the high-current, noisy, electrical devices are connected to these grounds as well as all of the sensor
returns. The sensor return comes into the sensor return circuit, passes through noise suppression, and is then con-
nected to the power ground.
The power ground is used to control ground circuits for the following PCM loads:
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Generator field winding
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Fuel injectors
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Ignition coil(s)
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Certain relays/solenoids
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Certain sensors
SENSOR RETURN
The Sensor Return circuits are internal to the Powertrain Control Module (PCM).
Sensor Return provides a low–noise ground reference for all engine control system sensors. Refer to Power
Grounds for more information.
OPERATION
PCM
The PCM operates the fuel system. The PCM is a pre-programmed, triple microprocessor digital computer. It reg-
ulates ignition timing, air-fuel ratio, emission control devices, charging system, certain transmission features, speed
control, air conditioning compressor clutch engagement and idle speed. The PCM can adapt its programming to
meet changing operating conditions.
The PCM receives input signals from various switches and sensors. Based on these inputs, the PCM regulates
various engine and vehicle operations through different system components. These components are referred to as
Powertrain Control Module (PCM) Outputs. The sensors and switches that provide inputs to the PCM are consid-
ered Powertrain Control Module (PCM) Inputs.
The PCM adjusts ignition timing based upon inputs it receives from sensors that react to: engine rpm, manifold
absolute pressure, engine coolant temperature, throttle position, transmission gear selection (automatic transmis-
sion), vehicle speed, power steering pump pressure, 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 generator charge
rate through control of the generator field and provides speed control operation.
NOTE: PCM Inputs:
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A/C request (if equipped with factory A/C)
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A/C select (if equipped with factory A/C)
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A/C pressure transducer
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Auto shutdown (ASD) sense
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Battery temperature
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Battery voltage
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Brake switch
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J1850 bus (+) circuits
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J1850 bus (-) circuits
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Camshaft position sensor signal
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Crankshaft position sensor
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Data link connection for scan tool
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Engine coolant temperature sensor
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ELECTRONIC CONTROL MODULES
KJ
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Fuel level (through J1850 circuitry)
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Generator (battery voltage) output
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Ignition circuit sense (ignition switch in on/off/crank/run position)
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Intake manifold air temperature sensor
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Knock sensors (2 on 3.7L engine)
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Leak detection pump (switch) sense (if equipped)
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Manifold absolute pressure (MAP) sensor
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Oil pressure
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Oxygen sensors
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Park/neutral switch (automatic transmission only)
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Power ground
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Power steering pressure switch
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Sensor return
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Signal ground
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Speed control multiplexed single wire input
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Throttle position sensor
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Transfer case switch (4WD range position)
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Vehicle speed sensor
NOTE: PCM Outputs:
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A/C clutch relay
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Auto shutdown (ASD) relay
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J1850 bus (+/-) circuits for: speedometer, voltmeter, fuel gauge, oil pressure gauge/lamp, engine temp. gauge
and speed control warn. lamp
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Clutch pedal position switch override relay
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Data link connection for scan tool
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EGR valve control solenoid (if equipped)
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EVAP canister purge solenoid
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Five volt sensor supply (primary)
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Five volt sensor supply (secondary)
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Fuel injectors
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Fuel pump relay
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Generator field driver (-)
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Generator field driver (+)
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Idle air control (IAC) motor
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Ignition coil(s)
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Leak detection pump (if equipped)
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Malfunction indicator lamp (Check engine lamp). Driven through J1850 circuits.
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Oxygen sensor heater relays
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Oxygen sensors (pulse width modulated)
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Radiator cooling fan relay (pulse width modulated)
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Speed control vacuum solenoid
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Speed control vent solenoid
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Tachometer (if equipped). Driven through J1850 circuits.
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Transmission convertor clutch circuit. Driven through J1850 circuits.
5 VOLT SUPPLIES
Primary 5 volt supply:
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supplies the required 5 volt power source to the Crankshaft Position (CKP) sensor.
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supplies the required 5 volt power source to the Camshaft Position (CMP) sensor.
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supplies a reference voltage for the Manifold Absolute Pressure (MAP) sensor.
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