Powertrain Control Module
Powertrain Control Module (PCM) Location:
SYSTEM OPERATION
The PCM operates the fuel system. The PCM was formerly referred to as the SBEC or engine controller. The PCM is a pre-programmed, triple microprocessor digital computer. It regulates ignition timing, air-fuel ratio, emission control devices, charging system, speed control (if equipped), 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 PCM Outputs. The sensors and switches that provide inputs to the PCM are considered 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 transmission), vehicle speed, power steering pump pressure (2.5L 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 generator charge rate through control of the generator field and provides speed control operation.
NOTE: Powertrain Control Module (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 connector for DRB scan tool
- Engine coolant temperature sensor
- Fuel level
- Generator (battery voltage) output
- Ignition circuit sense (ignition switch in run position)
- Intake manifold air temperature sensor
- Leak detection pump (if equipped)
- Manifold Absolute Pressure (MAP) sensor
- Oil pressure sensor
- Oxygen sensors
- Park/neutral switch (auto. trans. only)
- Power ground
- Power steering pressure switch (2.5L only)
- SCI receive (DRB scan tool 16-way connection)
- Sensor return
- Signal ground
- Speed control multiplexed single wire input
- Throttle position sensor
- Vehicle speed sensor
NOTE: Powertrain Control Module (PCM) Outputs:
- A/C clutch relay
- Auto Shutdown (ASD) relay
- CCD bus (+/-) circuits for: speedometer, voltmeter, fuel gauge, oil pressure gauge/lamp, engine temp. gauge and speed control warn. lamp
- Duty cycle EVAP canister purge solenoid
- Five volt sensor supply (primary)
- Five volt sensor supply (secondary)
- Fuel injectors
- Fuel pump relay
- Generator field driver (-)
- Generator field source (+)
- Idle Air Control (IAC) motor
- Ignition coil
- Leak detection pump (if equipped)
- Malfunction indicator lamp (Check engine lamp). Driven through CCD circuits.
- SCI transmit (DRB scan tool 16-way connection)
- Speed control vacuum solenoid
- Speed control vent solenoid
- Tachometer (if equipped). Driven through CCD circuits.
- Transmission convertor clutch solenoid
AIR CONDITIONING (A/C) CONTROLS-PCM INPUT
The A/C control system information applies to factory installed air conditioning units.
A/C SELECT SIGNAL: When the A/C switch is in the ON position, an input signal is sent to the Powertrain Control Module (PCM). The signal informs the PCM that the A/C has been selected. The PCM adjusts idle speed to a pre-programmed rpm through the Idle Air Control (IAC) motor to compensate for increased engine load.
A/C REQUEST SIGNAL: Once A/C has been selected, the powertrain control module (PCM) receives the A/C request signa]. from the clutch cycling pressure switch. The input indicates that the evaporator pressure is in the proper range for A/C application. The PCM uses this input to cycle the A/C compressor clutch (through the A/C relay). It will also determine the correct engine idle speed through the idle air control (IAC) motor position.
If the A/C low-pressure switch or high-pressure switch opens (indicating a low or high refrigerant pressure), the PCM will not receive an A/C request signal. The PCM will then remove the ground from the A/C relay. This will deactivate the A/C compressor clutch.
If the switch opens, (indicating that evaporator is not in proper pressure 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.
AUTOMATIC SHUTDOWN (ASD) RELAY SENSE-PCM INPUT
Power Distribution Center:
A 12 volt signal at this input indicates to the powertrain control module (PCM) that the ASD has been activated. The ASD relay is located in the Power Distribution Center (PDC). The PDC is located in the engine compartment. Refer to label on PDC cover for relay location. The ASD relay is used to connect the oxygen sensor heater elements, ignition coil, and fuel injectors to the 12 volt + power supply. Jeep models of previous years had used the ASD relay to apply the 12 volt + power supply to the generator field source (+) circuit. This generator circuit is now supplied 12 volts + directly from the PCM.
This input is used Only to sense that the ASD relay is energized. If the PCM does not see 12 volts at this input when the ASD should be activated, it will set a Diagnostic Trouble Code (DTC).
BATTERY TEMPERATURE SENSOR-PCM INPUT
Provides a signal to the PCM corresponding to the battery temperature.
BATTERY VOLTAGE-PCM INPUT
The battery voltage input provides power to the Powertrain Control Module (PCM). It also informs the PCM what voltage level is supplied to the ignition coil and fuel injectors.
If battery voltage is low, the PCM will increase injector pulse width (period of time that the injector is energized). This is done to compensate for the reduced flow through injector caused by the lowered voltage.
BRAKE SWITCH-PCM INPUT
When the brake light switch is activated, the Powertrain Control Module (PCM) receives an input indicating 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 Control (IAC) motor. The brake switch input is also used to disable vent and vacuum solenoid output signals to the speed control servo.
FIVE VOLT SENSOR SUPPLY-PRIMARY
Supplies the required 5 volt power source to the crankshaft position sensor, camshaft position sensor, MAP sensor and throttle position sensor.
FIVE VOLT SENSOR SUPPLY-SECONDARY
Supplies the required 5 volt source to the vehicle speed sensor.
FUEL LEVEL SENSOR-PCM INPUT
The Powertrain Control Module (PCM) supplies power to the fuel level sensor (fuel gauge sending unit). The fuel level sensor will then return a signal to the PCM to indicate fuel level. The purpose of this feature is to prevent a false setting of misfire and fuel system monitor trouble codes. This is if the fuel level is less than approximately 15 percent, or, if equipped with a Leak Detection Pump (LDP), more than approximately 85 percent of its rated capacity. This input is also used to send a signal to the PCM for fuel gauge operation via the CCD bus circuits.
CAMSHAFT POSITION SENSOR-PCM INPUT
Camshaft Position Sensor - Typical:
A sync signal is provide by the camshaft position sensor located in the distributor. The sync signal from this sensor works in conjunction with the crankshaft position sensor to provide the Powertrain Control Module (PCM) with inputs. This is done to establish and maintain correct injector firing order.
CRANKSHAFT POSITION SENSOR-PCM INPUT
This sensor is a hall effect device that detects notches in the flywheel (manual transmission) or flexplate (automatic transmission).
This sensor is used to indicate to the Powertrain Control Module (PCM) that a spark and or fuel injection event is to be required. The output from this sensor, in conjunction with the camshaft position sensor signal, is used to differentiate between fuel injection and spark events.
The sensor is bolted to the transmission bellhousing.
ENGINE COOLANT TEMPERATURE SENSOR-PCM INPUT
Engine Coolant Temperature Sensor - Typical:
The engine coolant temperature sensor is installed in the thermostat housing and protrudes into the water jacket. The sensor provides an input voltage to the Powertrain Control Module (PCM) relating coolant temperature. The PCM uses this input along with inputs from other sensors to determine injector pulse width and ignition timing. As coolant temperature varies, the coolant temperature sensor's resistance changes. The change in resistance results in a different input voltage to the PCM.
When the engine is cold, the PCM will operate in Open Loop cycle. It will demand slightly richer air-fuel mixtures and higher idle speeds. This is done until normal operating temperatures are reached.
Refer to Open Loop/Closed Loop Modes of Operation for more information.
GENERATOR OUTPUT-PCM INPUT
Provides a charging system voltage input to the Powertrain Control Module (PCM). It is sensed at the battery input to the PCM.
OXYGEN SENSOR (O2S)-PCM INPUT
Two heated O2S sensors are used. When the key is turned ON, and the engine is cold, the sensors will have an initial voltage of 5 volts. The sensors themselves produce voltages from 0 to 1 volt, depending upon the oxygen content of the exhaust gas in the exhaust manifold. When a large amount of oxygen is present (caused by a lean air/fuel mixture), the sensors produces a low voltage. When there is a lesser amount present (rich air/fuel mixture) it produces a higher voltage. By monitoring the oxygen content and converting it to electrical voltage, the sensors act as a rich-lean switch.
Both oxygen sensors are equipped with a heating element that reduces the time required for the sensors to reach operating temperature allowing the system to enter into closed loop operation sooner. Maintaining correct sensor temperature at all times allows the system to remain in closed loop operation during periods of extended idle. The Automatic Shutdown (ASD) relay supplies battery voltage to both the upstream and downstream oxygen sensor heating elements.
In Closed Loop operation, the Powertrain Control Module (PCM) monitors both O2S sensor inputs (along with other inputs) and adjusts the injector pulse width accordingly. During Open Loop operation, the PCM ignores the O2S sensor input. The PCM adjusts injector pulse width based on preprogrammed (fixed) values and inputs from other sensors.
For more O2S information, refer to Monitored Systems in Emission Control Systems.
UPSTREAM HEATED OXYGEN SENSOR
Upstream Oxygen Sensor:
The upstream O2S sensor is located in the exhaust downpipe. It provides an input voltage to the PCM. The input tells the PCM the oxygen content of the exhaust gas. The PCM uses this information to fine tune the air/fuel ratio by adjusting injector pulse width.
DOWNSTREAM HEATED OXYGEN SENSOR
Downstream Oxygen Sensor:
The downstream heated oxygen sensor is located near the outlet end of the catalytic convertor. The downstream heated oxygen sensor input is used to detect catalytic convertor deterioration and provide fuel adjustment information.
As the convertor deteriorates, the input from the downstream sensor begins to match the upstream sensor input except for a slight time delay. By comparing the downstream heated oxygen sensor input to the input from the upstream sensor, the PCM calculates catalytic convertor efficiency.
When the catalytic converter efficiency drops below emission standards, the PCM stores a diagnostic trouble code and illuminates the Malfunction Indicator (MIL) (or Check Engine) lamp. For more information, refer to Emission Control Systems.
The downstream sensor input is also used to adjust the upstream O2S goal voltage. This allows a better control of the exhaust gases as the catalytic convertor ages.
The upstream and downstream sensors may look exactly alike, but are not interchangeable.
IGNITION CIRCUIT SENSE-PCM INPUT
The ignition circuit sense input tells the Powertrain Control Module (PCM) the ignition switch has energized the ignition circuit.
INTAKE MANIFOLD AIR TEMPERATURE SENSOR-PCM INPUT
Intake Man. Air Temp. Sensor Location:
Intake Man. Air Temp. Sensor Location:
The intake manifold air temperature sensor is installed in the intake manifold with the sensor element extending into the air stream. The sensor provides an input voltage to the Powertrain Control Module (PCM) indicating intake manifold air temperature. The input is used along with inputs from other sensors to determine injector pulse width. As the temperature of the air-fuel stream in the manifold varies, the sensor resistance changes. This results in a different input voltage to the PCM.
LEAK DETECTION PUMP (SWITCH) SENSE-PCM INPUT
Provides an input to the PCM that the leak detection pump (LDP) has been activated. Refer to Emission Control System for LDP information.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR-PCM INPUT
The MAP sensor reacts to absolute pressure in the intake manifold. It provides an input voltage to the Powertrain Control Module (PCM). As engine Toad changes, manifold pressure varies. The change in manifold pressure causes MAP sensor voltage to change. The change in MAP sensor voltage results in a different input voltage to the PCM. The input voltage level supplies the PCM with information about ambient barometric pressure during engine load while the engine is running. The PCM uses this input along with inputs from other sensors to adjust air-fuel mixture.
The MAP sensor is mounted on the side of the engine throttle body. The sensor is connected to the throttle body with a rubber L-shaped fitting.
OIL PRESSURE SENSOR-PCM INPUT
Sends a signal from the oil pressure sending unit to the Powertrain Control Module (PCM) relating to engine oil pressure.
POWER GROUND
The power ground is used to control ground circuits for the following powertrain control module (PCM) loads:
- Generator field winding
- Fuel injectors
- Ignition coil
- Certain relays/solenoids
POWER STEERING PRESSURE SWITCH-PCM INPUT
Power Steering Pump Pressure Switch:
A pressure sensing switch is included in the power steering system (mounted on the high-pressure line). This switch will be used only on vehicles equipped with a 2.5L engine and power steering. The switch provides an input to the Powertrain Control Module (PCM). This input is provided during periods of high pump load and low engine rpm; such as during parking maneuvers. The PCM will then increase the idle speed through the Idle Air Control (IAC) motor. This is done to prevent the engine from stalling under the increased load.
When steering pump pressure exceeds 3275 kPa ± 690 kPa (475 psi ± 100 psi), the normally closed switch will open and the PCM will increase the engine idle speed. This will prevent the engine from stalling.
When pump pressure drops to approximately 1379 kPa (200 psi), the switch circuit will re-close and engine idle speed will return to its previous setting.
SENSOR RETURN-PCM INPUT
Sensor Return provides a low noise ground reference for all engine control system sensors.
SPEED CONTROL SWITCHES-PCM INPUT
Two separate speed control switch modules are mounted on the steering wheel to the left and right side of the driver's airbag module. Within the two switch modules, five momentary contact switches, supporting seven different speed control functions are used. The outputs from these switches are filtered into one input. The Powertrain Control Module (PCM) determines which output has been applied through resistive multiplexing. The input circuit voltage is measured by the PCM to determine which switch function has been selected.
A speed control indicator lamp, located on the instrument panel cluster is energized by the PCM via the CCD Bus. This occurs when speed control system power has been turned ON, and the engine is running.
The two switch modules are labeled: ON/OFF SET, RESUME/ACCEL, CANCEL and COAST. Refer to Speed Control System for more information.
TRANSMISSION PARK/NEUTRAL SWITCH-PCM INPUT
The park/neutral switch is located on the transmission housing and provides an input to the Powertrain Control Module (PCM). This will indicate that the automatic transmission is in Park, Neutral or a drive gear selection. This input is used to determine idle speed (varying with gear selection), fuel injector pulse width and ignition timing advance. It is also used as a condition for speed control operation.
THROTTLE POSITION SENSOR (TPS)-PCM INPUT
Intake Man. Air Temp. Sensor Location:
The TPS is mounted on the throttle body. The TPS is a variable resistor that provides the Powertrain Control Module (PCM) with an input signal (voltage) that represents throttle blade position. The sensor is connected to the throttle blade shaft. As the position of the throttle blade changes, the resistance of the TPS changes.
The PCM supplies approximately 5 volts to the TPS. The TPS output voltage (input signal to the PCM) represents the throttle blade position. The PCM receives an input signal voltage from the TPS. This will vary in an approximate range of from 0.26 volts at minimum throttle opening (idle), to 4.49 volts at wide open throttle. Along with inputs from other sensors, the PCM uses the TPS input to determine current engine operating conditions. In response to engine operating conditions, the PCM will adjust fuel injector pulse width and ignition timing.
VEHICLE SPEED AND DISTANCE SENSOR-PCM INPUT
Vehicle Speed Sensor Location - Typical:
The vehicle speed sensor is located on the speedometer pinion gear adapter. The pinion gear adapter is located on the extension housing of the transfer case (drivers side). The sensor input is used by the Powertrain Control Module (PCM) to determine vehicle speed and distance traveled.
The speed sensor generates 8 pulses per sensor revolution. These signals, in conjunction with a closed throttle signal from the throttle position sensor, indicate a closed throttle deceleration to the PCM. When the vehicle is stopped at idle, a closed throttle signal is received by the PCM (but a speed sensor signal is not received).
Under deceleration conditions, the PCM adjusts the Idle Air Control (IAC) motor to maintain a desired MAP value. Under idle conditions, the PCM adjusts the IAC motor to maintain a desired engine speed.
AIR CONDITIONING (A/C) CLUTCH RELAY-PCM OUTPUT
Power Distribution Center:
The A/C relay is located in the Power Distribution Center (PDC). The PDC is located in the engine compartment. Refer to label on PDC cover for relay location.
The powertrain control module (PCM) activates the A/C compressor through the A/C clutch relay. The PCM regulates A/C compressor operation by switching the ground circuit for the A/C clutch relay on and off.
When the PCM receives a request for A/C from A/C evaporator switch, it will adjust idle air control (IAC) motor position. This is done to increase idle speed. The PCM will then activate the A/C clutch through the A/C clutch relay. The PCM adjusts idle air control (IAC) stepper motor position to compensate for increased engine load from the A/C compressor.
By switching the ground path for the relay on and off, the PCM is able to cycle the A/C compressor clutch. This is based on changes in engine operating conditions. The PCM Will also de-energize the relay if coolant temperature exceeds 125° C (257° F).
AUTO SHUTDOWN (ASD) RELAY-PCM OUTPUT
The ASD relay is located in the Power Distribution Center (PDC).
The ASD supplies battery voltage to the fuel injectors, ignition coil and oxygen (O2S) sensor beating elements. The ground circuit for the coil in the ASD relay is controlled by the powertrain control module (PCM). The PCM operates the relay by switching the ground circuit on and off.
CCD BUS (+1-) CIRCUITS-PCM OUTPUTS
The Powertrain Control Module (PCM) sends certain output signals through the CCD bus circuits. These signals are used to control certain instrument panel located items and to determine certain identification numbers.
DATA LINK CONNECTOR-PCM INPUT AND OUTPUT
Data Link Connector Location:
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 is located under the instrument panel to the left of the steering column. For operation of the DRB scan tool, refer to the appropriate Powertrain Diagnostic Procedures service manual.
DUTY CYCLE EVAP PURGE SOLENOID VALVE-PCM OUTPUT
Refer to Emission Control System for information.
FUEL INJECTORS-PCM OUTPUT
Fuel Injectors - Typical:
Six individual fuel injectors are used with the 4.0L 6-cylinder engine. Four individual fuel injectors are used with the 2.5L 4-cylinder engine. The injectors are attached to the fuel rail.
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.
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.
During start up, battery voltage is supplied to the injectors through the ASD relay. When the engine is operating, voltage is supplied by the charging system. The PCM determines injector pulse width based on various inputs.
FUEL PUMP RELAY-PCM OUTPUT
The PCM energizes the electric fuel pump through the fuel pump relay. Battery voltage is applied to the fuel pump relay when the ignition key is ON. The relay is energized when a ground signal is provided by the PCM.
The fuel pump will operate for approximately three seconds unless the engine is operating or the starter motor is engaged.
The fuel pump relay is located in the Power Distribution Center (PDC).
GENERATOR FIELD SOURCE (+)-PCM OUTPUT
This output from the Powertrain Control Module (PCM) regulates charging system voltage to the generator field source (+) circuit. The voltage range is 12.9 to 15.0 volts. Models of previous years had used the ASD relay (directly) to apply the 12 volt + power supply to the generator field source (+) circuit. Refer to charging system information.
GENERATOR FIELD DRIVER (-)-PCM OUTPUT
This output from the Powertrain Control Module (PCM) regulates charging system ground control to the generator field driver (-) circuit. Refer to charging system information.
IDLE AIR CONTROL (IAC) MOTOR-PCM OUTPUT
Intake Man. Air Temp. Sensor Location:
The IAC motor is mounted on the throttle body and is controlled by the Powertrain Control Module (PCM).
The throttle body has an air control passage that provides air for the engine at idle (the throttle plate is closed). The IAC motor pintle protrudes into the air control passage and regulates air flow through it. Based on various sensor inputs, the PCM adjusts engine idle speed by moving the IAC motor pintle in and out of the air control passage. The IAC motor is positioned when the ignition key is turned to the On position.
A (factory adjusted) set screw is used to mechanically limit the position of the throttle body throttle plate. Never attempt to adjust the engine idle speed using this screw. All idle speed functions are controlled by the PCM.
IGNITION COIL-PCM OUTPUT
System voltage from the Automatic Shutdown (ASD) relay is supplied to the ignition coil positive terminal. The Powertrain Control Module (PCM) operates the ignition coil. Ignition timing is not adjustable. The PCM adjusts ignition timing to meet changing engine operating conditions.
Refer to Ignition System for additional information.
LEAK DETECTION PUMP-PCM OUTPUT
Certain engines with certain emissions packages are equipped with a leak detection pump (LDP). The LDP is activated through this PCM output. Refer to Emission Control System for additional information.
MALFUNCTION INDICATOR LAMP-ECM/PCM OUTPUT
Refer to Emission Control System for information.
SPEED CONTROL SOLENOIDS-PCM OUTPUT
Speed control operation is regulated by the powertrain control module (PCM). The PCM controls the vacuum to the throttle actuator through the speed control vacuum and vent solenoids. Refer to Speed Control Information.
TACHOMETER-PCM OUTPUT
The powertrain control module (PCM) supplies engine rpm values to the instrument cluster tachometer.