Engine Controls - Theory & Operation: Other Dodge Durango I

POWERTRAIN CONTROL MODULE (PCM)

The PCM is a digital computer that controls ignition timing, air/fuel ratio, fuel injector pulse width, ignition coil(s), spark advance, emission control devices, cooling fan, charging system, idle speed, cruise control (if equipped), fuel pump and tachometer. For PCM location, see PCM LOCATION table. PCM uses data from various input sources to control output devices in order to achieve optimum engine performance for all operating conditions.

PCM has voltage converters that convert battery voltage to regulated 5-volt output. The 5-volt output powers battery temperature sensor, Camshaft Position (CMP) sensor on models equipped with Distributorless Ignition System (DIS) or distributor on models without DIS, Crankshaft Position (CKP) sensor, Engine Coolant Temperature (ECT) sensor, Intake Air Temperature (IAT) sensor, logic circuits, Manifold Absolute Pressure (MAP) sensor, Throttle Position (TP) sensor and Vehicle Speed Sensor (VSS) on some models.

PCM LOCATION

INPUT DEVICES

Note. Components are grouped into 2 categories. The first category, INPUT DEVICES , includes components that control or produce voltage signals monitored by the PCM. The second category, OUTPUT SIGNALS , includes components controlled by the PCM (this is accomplished by the PCM grounding individual circuits).

Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine component location and input usage on a specific model, see WIRING DIAGRAMS article. Available input signals include

A/C Switch (All Models)

Switch signals PCM that A/C has been selected. PCM then activates A/C compressor clutch relay and maintains idle speed at a preprogrammed RPM. This is done through control of Idle Air Control (IAC) motor.

Battery Temperature Sensor (All Models)

PCM uses sensor to determine battery temperature and to control battery charging rate. Temperature data along with battery voltage data, is used by PCM to vary charging rate. System voltage is higher at colder temperatures and is gradually reduced at warmer temperatures.

Battery Voltage (All Models)

PCM monitors battery voltage to determine fuel injector pulse width and generator field control. This is done to compensate for reduced current flow through injector caused by lowered voltage.

Brake Switch (All Models)

This switch may also be referred to as a brakelight switch. PCM uses this switch input to maintain idle speed at a preprogrammed RPM when brakes are applied. If PCM receives an input signal from brake switch when speed control system is on, PCM will turn speed control system off.

Camshaft Position (CMP) Sensor (All Models)

On models with distributors, CMP sensor is made up of a Hall Effect switch (sync signal generator) and a rotating pulse ring (shutter) located on the distributor shaft. (Scheme 1) On models with Distributorless Ignition System (DIS), CMP sensor reads slots in cam timing sprocket. On all models, PCM uses this information along with information from Crankshaft Position (CKP) sensor to determine if fuel injectors and ignition coils are properly sequenced for correct cylinders.

Scheme 1

Crankshaft Position (CKP) Sensor (All Models)

On 2.5L, 3.9L, 5.2L and 5.9L models, CKP sensor is mounted on or near outer edge of bellhousing and detects sets of slots on flywheel/torque converter drive plate. On 4.7L and 8.0L models, CKP sensor is mounted to right lower side of engine block and detects sets of slots on crankshaft sprocket. PCM uses this information to determine fuel injection sequence, ignition signal and spark timing.

Cruise Control Switch (All Models)

Cruise control switch provides PCM with 3 separate inputs. ON/OFF switch input informs PCM that cruise control system has been activated. SET/COAST switch input informs PCM that set vehicle speed has been selected, or if depressed will decelerate until switch is released. RESUME/ACCEL switch input informs PCM that a previously set speed has been selected or, if depressed, will increase speed until released. PCM uses these inputs to control cruise control servo.

Engine Coolant Temperature (ECT) Sensor (All Models)

ECT sensor monitors engine coolant temperature. PCM uses ECT sensor information to adjust air/fuel mixture and idle speed and to control radiator cooling fans as necessary.

Fuel Level Sensor (All Models)

PCM supplies a 5-volt reference signal to fuel module in gas tank. Fuel level sensor sends a signal to PCM indicating fuel level. PCM monitors this signal to prevent a false misfire signal if fuel level is less than 15 percent. PCM also sends this signal to fuel gauge.

Heated Oxygen Sensor (All Models)

Heated Oxygen Sensor (HO2S) produces a small electrical voltage (0-1 volt) when exposed to heated exhaust gas. HO2S is electrically heated for faster warm-up. Heating element is powered through Auto Shutdown (ASD) relay.

HO2S acts like a rich/lean (air/fuel ratio) switch by monitoring oxygen content in exhaust gas. This information is used by PCM to adjust air/fuel ratio by adjusting injector pulse width.

HO2S produces low voltage when oxygen content in exhaust gas is high. When oxygen content in exhaust gas is low, HO2S produces a higher voltage.

Ignition Switch (All Models)

Ignition switch sends signal to PCM indicating whether switch is on, off or cranking (ST). When PCM receives ON signal, it energizes ASD relay coil and supplies power to sensors and actuators. When PCM receives ST signal, it controls fuel injection rate, idle speed, ignition timing, etc. for optimum cranking conditions.

Intake Air Temperature Sensor (All Models)

Intake Air Temperature (IAT) sensor measures temperature of incoming intake air. This information is used by PCM to adjust air/fuel mixture.

Manifold Absolute Pressure Sensor (All Models)

Manifold Absolute Pressure (MAP) sensor monitors intake manifold vacuum. Sensor transmits information on manifold vacuum and barometric pressure to PCM. MAP sensor information is used with information from other sensors to adjust air/fuel mixture.

Oil Pressure Sensor (All Models)

Oil pressure sensor sends a signal to PCM to indicate oil pressure.

Output Speed Sensor (All Models)

Note. On 4.7L models, the OSS signal is sent to the TCM, which in turn sends it to the PCM.

Models equipped with an overdrive A/T use a transmission Output Speed Sensor (OSS). OSS is located on output shaft housing of transmission. OSS delivers input signal to Powertrain Control Module (PCM) to indicate transmission output shaft speed.

Park/Neutral (P/N) Switch (A/T Models)

This switch may also be referred to as a Park/Neutral Position (PNP) switch. P/N switch is available on vehicles equipped with A/T only. Switch prevents engine starter from engaging if vehicle is in any gear except Park or Neutral. P/N switch input (varied with gear selection) is used to determine idle speed, fuel injector pulse and ignition timing.

Power Steering Pressure (PSP) Switch (2.5L & 4.7L)

PSP switch sends a signal to PCM. PCM will raise idle speed to prevent stalling during high power steering pressure 375-575 psi (2586-3965 kPa), low RPM conditions.

Rear Anti-Lock Brake System Wheel Speed Sensor (All Models)

The vehicle speed and distance traveled are determined by rear wheel speed sensor. Rear wheel speed sensor is mounted on top of rear axle housing, above the ring gear. The rear ABS wheel speed sensor provides a wheel speed signal to the Controller Anti-Lock Brake (CAB). The CAB then sends an input signal to indicate vehicle speed and distance traveled through CCD Bus circuits to the Powertrain Control Module (PCM).

PCM uses input signal for controlling cruise control system, fuel system and automatic transmission (if equipped). The CAB is mounted on top of the hydraulic control unit. Hydraulic control unit contains the pump assembly that brakelines are attached to and is mounted in the engine compartment. On 4.7L models, a vehicle speed signal is sent to the Transmission Control Module (TCM).

Serial Communication Interface (SCI) Receive (All Models)

SCI receive circuit is a serial communication link used when diagnosing vehicle using scan tool. PCM receives data and device activation commands from scan tool on this circuit.

Throttle Position Sensor (All Models)

Throttle Position (TP) sensor monitors opening angle of throttle blade. TP sensor will vary output voltage from about .26 volt at minimum throttle opening (idle), to about 4.5 volts at Wide Open Throttle (WOT). PCM uses this information and other sensor inputs to determine engine operation. In response, PCM will adjust fuel injection pulse width and ignition timing.

Transmission Governor Pressure Sensor (A/T Models)

Sensor sends PCM a signal indicating governor pressure. PCM uses signal as feedback for governor solenoid control. For additional information, see appropriate ELECTRONIC CONTROLS article in AUTOMATIC TRANSMISSIONS.

Transmission Overdrive/Override (OD/OR) Switch (A/T Models)

On models with Overdrive (OD), PCM regulates 3-4 OD upshift and downshift through OD solenoid. Transmission OD/OR switch is mounted in instrument panel. OD/OR switch is normally closed. If OD/OR switch is depressed and it opens, transmission will not enter OD. Transmission will downshift if it is in OD and OD/OR switch is depressed.

OD/OR switch circuit includes a transmission fluid temperature sensor. If this sensor opens, transmission will not shift into overdrive, or will downshift if already in overdrive. For additional information, see appropriate ELECTRONIC CONTROLS article in AUTOMATIC TRANSMISSIONS.

Transmission Temperature Sensor (A/T Models)

Transmission temperature sensor monitors transmission fluid temperature and sends an input signal to PCM. Input signal is used for controlling torque converter clutch operation, overdrive shifts, low temperature shift compensation, wide open throttle shift strategy and governor pressure. Transmission temperature sensor is located in transmission valve body, incorporated into governor pressure sensor.

If transmission fluid temperature is more than 260°F (126°C), PCM forces a 4-3 downshift and engages torque converter clutch until fluid cools. Once fluid cools to less than 230°F (110°C), PCM allows a 3-4 shift. PCM prevents torque converter clutch engagement and overdrive operation when fluid temperature is less than 50°F (10°C).

OUTPUT SIGNALS

Note. Each vehicle may be equipped with different combinations of computer-controlled components. The following components may NOT be used on all models. To determine component location, see appropriate wiring diagram in appropriate WIRING DIAGRAMS article. For theory and operation on each output component, refer to indicated system.

A/C Clutch Relay

See A/C CLUTCH RELAY under MISCELLANEOUS CONTROLS.

Auto Shutdown (ASD) Relay

See AUTO SHUTDOWN (ASD) RELAY & FUEL PUMP RELAY under MISCELLANEOUS CONTROLS.

Distributorless Ignition System (DIS)

See DISTRIBUTORLESS IGNITION SYSTEM (DIS) under IGNITION SYSTEM.

Evaporative Canister Purge Control Solenoid (EVAP-CPCS)

See EVAPORATIVE (EVAP) EMISSIONS SYSTEM under EMISSION SYSTEMS.

Fuel Injectors

See FUEL CONTROL under FUEL SYSTEM.

Fuel Pump Relay

See AUTO SHUTDOWN (ASD) RELAY & FUEL PUMP RELAY under MISCELLANEOUS CONTROLS.

Generator

See GENERATOR under MISCELLANEOUS CONTROLS.

Idle Air Control (IAC) Motor

See IDLE SPEED under FUEL SYSTEM.

Ignition Coil

See IGNITION SYSTEM .

In-Tank Fuel Pump

See FUEL DELIVERY under FUEL SYSTEM.

Limp-In Mode

See LIMP-IN MODE under MISCELLANEOUS CONTROLS.

Malfunction Indicator Light (MIL)

See MALFUNCTION INDICATOR LIGHT under SELF-DIAGNOSTIC SYSTEM.

Radiator Fan Relay

See RADIATOR FAN RELAY under MISCELLANEOUS CONTROLS.

Serial Communications Interface (SCI) Transmit

See SERIAL COMMUNICATIONS INTERFACE (SCI) under SELF-DIAGNOSTIC SYSTEM.

Shift Indicator Light

See SHIFT INDICATOR LIGHT under MISCELLANEOUS CONTROLS.

Speed Control Servo

See SPEED CONTROL SERVO under MISCELLANEOUS CONTROLS.

Tachometer

See TACHOMETER under MISCELLANEOUS CONTROLS.

Transmission Governor Pressure Solenoid

See TRANSMISSION GOVERNOR SOLENOID under MISCELLANEOUS CONTROLS.

Transmission Overdrive/Override (OD/OR) Switch Indicator Light

See TRANSMISSION OVERDRIVE/OVERRIDE (OD/OR) SWITCH INDICATOR under MISCELLANEOUS CONTROLS.

Transmission Overdrive (OD) Solenoid

See TRANSMISSION OVERDRIVE (OD) SOLENOID under MISCELLANEOUS CONTROLS.

See AUTO SHUTDOWN (ASD) RELAY & FUEL PUMP RELAY under MISCELLANEOUS CONTROLS.

Fuel Pressure Regulator

Fuel pressure regulator is a mechanical device, used to maintain a constant pressure across fuel injector tip. Spring and rubber diaphragm will move from an open to closed position keeping fuel pressure constant. Excess fuel is returned to fuel tank.

Fuel pressure regulator is located in in-tank fuel pump module. Fuel pressure regulator includes an internal fuel filter. Excess fuel is routed directly into fuel tank without using a return line. (Scheme 2)

Scheme 2

Fuel pump is a positive displacement, immersible pump with a permanent magnet electric motor. Fuel is drawn in through a separate filter/strainer at bottom of fuel pump and pushed through filter to fuel outlet line (to fuel injectors). Voltage to operate pump is supplied from fuel pump relay. On some models, fuel pump relay is activated by ASD relay.

Fuel pump module includes a combination fuel filter/fuel pressure regulator, fuel pump reservoir, a separate in-tank fuel filter, pressure relief/rollover valve, fuel gauge sending unit and fuel supply line. (Scheme 3)

Scheme 3

Fuel injectors are electric solenoid valves controlled by PCM. PCM determines when and length of time (pulse width) injectors should operate by switching ground path on and off. During start-up, battery voltage is supplied to injectors through ASD relay. On some models, battery voltage is supplied by charging system once engine is operating. When ground is supplied to injector by PCM, armature and pintle inside injector move a short distance against spring and open a small orifice. Since fuel is under high pressure, a fine spray is developed.

Sequential Fuel Injection (SFI)

Individual, electrically pulsed injectors (one per cylinder) are located in intake manifold runners. These injectors are next to intake valves in intake manifold. PCM controls injection timing based on crankshaft position signal input. PCM regulates air/fuel mixture by length of time injector stays open (pulse width) based on inputs from HO2S, ECT sensor, MAP and other sensors.

IDLE SPEED

Note. DO NOT attempt to correct a high idle speed condition by turning factory sealed throttle body throttle plate set screw. This will not change idle speed of warm engine, but may cause cold start problems due to restricted airflow.

IAC motor adjusts idle speed to compensate for engine load and ambient temperature by adjusting amount of air flowing through by-pass in back of throttle body. PCM uses ECT sensor, VSS, TP sensor and various switch input operations to adjust IAC motor to obtain optimum idle conditions. Deceleration stall is prevented by increasing airflow when throttle is closed suddenly.

IGNITION SYSTEM

The PCM completely controls ignition system. During crank/start mode, PCM will set a fixed amount of spark advance for an efficient engine start. Amount of spark advance or retard is determined by inputs that PCM receives from ECT sensor, MAP sensor and engine RPM. During engine operation, PCM can supply an infinite number of advance curves to ensure proper engine operation.

Ram Pickup 8.0L

DIS eliminates mechanical ignition components that can wear out. PCM has complete ignition control and uses a coil pack, CMP sensor and CKP sensor to control ignition timing. CMP sensor reads slots in cam timing sprocket. PCM uses this information along with information from CKP sensor to determine if fuel injectors and ignition coils are properly sequenced for correct cylinders.

Basic timing is determined by CKP sensor position and is not adjustable. One complete engine revolution may be required for PCM to determine crankshaft position during cranking.

Molded ignition coils are used. Each coil fires 2 paired spark plugs at the same time. One cylinder is on compression stroke and other cylinder is on exhaust stroke.

Except Ram Pickup 8.0L

This system is equipped with a Hall Effect distributor. (Scheme 1) Shutter(s) attached to distributor shaft rotate through distributor Hall Effect switch, also referred to as a CMP sensor, which contains a distributor pick-up (a Hall Effect device and magnet). As shutter blade(s) pass through pick-up, magnetic field is interrupted and voltage is toggled between high and low. PCM uses this cylinder position data from CMP sensor, along with engine speed (RPM) and CKP sensor data, to control ignition timing and injector pulse width to maintain optimum driveability.

EMISSION SYSTEMS

Vehicles are equipped with different combinations of emission system components. Not all components are used on all models.

5.9L & 8.0L Heavy Duty Cycle (HDC)

This system adds a controlled amount of air to exhaust gases, through air relief valve and check valves, to assist oxidation of hydrocarbons and carbon monoxide in exhaust stream. Air is injected at catalytic converters.

8.0L

CCV system performs same function as a conventional Positive Crankcase Ventilation (PCV) system, but does not use a vacuum controlled valve. See POSITIVE CRANKCASE VENTILATION (PCV) .

EVAPORATIVE (EVAP) EMISSIONS SYSTEM

This system stores fuel vapors from fuel tank, preventing vapors from reaching the atmosphere. As fuel evaporates inside fuel tank, vapors are routed through vent hoses to charcoal canister where they are stored until engine is started.

Charcoal canister purging is controlled by PCM through an EVAP-CPCS. During engine warm-up and for a short period after hot restarts, PCM energizes EVAP-CPCS, interrupting engine vacuum signal to charcoal canister.

After engine reaches a predetermined operating temperature and PCM internal timer has expired, PCM will de-energize EVAP-CPCS, allowing engine vacuum to purge charcoal canister. EVAP-CPCS will also be de-energized during certain idle conditions so PCM can update fuel delivery calibration.

POSITIVE CRANKCASE VENTILATION (PCV)

PCV system uses a vacuum-operated valve. A closed engine crankcase breather/filter, with a hose connecting it to air filter housing, provides source of air for system. Crankcase blow-by gases are removed from crankcase through PCV valve with manifold vacuum. These gases are introduced into incoming air/fuel mixture and become part of the calibrated mixture.

A non-vacuum operated Crankcase Ventilation (CCV) system is used on some engines, see CRANKCASE VENTILATION (CCV) SYSTEM .

CCD BUS

The CCD Bus is a 2 wire communication port in which controllers and modules exchange information. PCM transmits monitored input information and control requests to other modules on CCD Bus. PCM also receives information and requests from other controllers that will effect the control of its outputs. The CCD Bus has a measurable voltage of about 2.5 volts.

The following items transmit or receive information from PCM through the CCD Bus

1. Air Conditioning Switch Transmits A/C select command inputs to PCM.
2. Air Conditioning Evaporator Temperature Sensor Transmits evaporator temperature input to PCM.
3. Park/Neutral Position Switch Transmits transmission gear position to PCM.
4. Speed (Cruise) Control Switch Transmits speed control engage command inputs to PCM.
5. Malfunction Indicator Light (MIL) Receives On/Off command from PCM.
6. Engine RPM (Tachometer) Receives engine RPM signal from PCM.

The following components access or send information on the CCD Bus

1. Air Bag System Diagnostic Module (ABSDM).
2. Controller Anti-lock Brake (CAB).
3. Body Control Module (BCM).
4. Full Automatic Temperature Control (ATC) display head.
5. Instrument Panel (I/P).
6. Powertrain Control Module (PCM).
7. Transmission Control Module (TCM), if equipped.
8. Traveler module (if equipped).

MALFUNCTION INDICATOR LIGHT

Malfunction Indicator Light (MIL) comes on and remains on for 3 seconds as a bulb test each time ignition switch is turned to ON position. If PCM receives an incorrect signal or receives no signal from battery voltage input, charging system, ECT sensor, MAP sensor or TP sensor, MIL will come on. MIL will also come on if certain emission-related faults exist. This warns driver that PCM is in limp-in mode and immediate repairs are necessary. See LIMP-IN MODE under MISCELLANEOUS CONTROLS. MIL can also be used to display Diagnostic Trouble Codes (DTCs). For additional information, see appropriate SELF-DIAGNOSTICS article.

PCI BUS SYSTEM

Note. For additional information on PCI system communications, see appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.

The Programmable Communication Interface (PCI bus) multiplex system consists of a single wire. The BCM acts as a splice to connect each module and DLC. Each module uses its local ground as bus reference. If more than one module is trying to access the PCI bus at one time, the code being sent determines which message has higher priority, and is then allowed to access bus first. Communication over the bus is essential to proper operation of vehicles on-board diagnostic systems and Diagnostic Readout Box (DRB-III(R)). Problems with operation of bus or DRB-III(R) must be corrected before proceeding with diagnostic testing.

SERIAL COMMUNICATIONS INTERFACE (SCI)

SCI circuit is used by PCM to send data to and receive data and sensor activation signals from scan tool. Scan tool uses signals sent on SCI to display fault messages or Diagnostic Trouble Codes (DTCs), sensor voltages and device states (On/Off). Scan tool uses SCI to send solenoid and switch activation commands to PCM so that devices and circuits can be tested. SCI is also used to write SRI mileage to PCM.

MISCELLANEOUS CONTROLS

Note. Although not strictly considered part of engine performance system, some controlled devices can adversely affect driveability if they malfunction.

All Models

A/C clutch relay is controlled by PCM. When A/C or Defrost mode is selected and PCM receives A/C request signal from evaporator switch, PCM will cycle clutch on and off through A/C clutch relay. When this relay is energized during engine operation, PCM will determine correct engine idle speed through IAC motor.

When PCM senses low idle speed or wide open throttle through TP sensor, PCM will de-energize A/C clutch relay, preventing A/C operation.

ASD relay and electric fuel pump relay are energized when ignition is on. These relays are controlled through PCM by switching a common ground circuit on and off. Following components are controlled by ASD and fuel pump relays

1. Electric Fuel Pump
2. Fuel Injectors
3. Generator Field Winding
4. Ignition Coil(s)
5. HO2S Heating Element

When ignition switch is turned to RUN position, PCM energizes ASD relay and electric fuel pump relay which powers these components. If PCM does not receive a CMP and CKP sensor signal within one second of engine cranking (start-up), PCM will turn ground circuit off and de-energize ASD relay.

Powertrain Control Module (PCM) regulates charging system voltage. For additional information on charging system, see GENERATORS & REGULATORS - TRUCKS & RWD VANS article in STARTING & CHARGING SYSTEMS.

Limp-in mode is the attempt by PCM to compensate for failure of certain components by substituting information from other sources so that vehicle can still be operated. If PCM senses incorrect data or no data at all from MAP sensor, TP sensor, ECT sensor or battery voltage, system is placed into limp-in mode and Malfunction Indicator Light (MIL) on instrument panel comes on.

If faulty sensor comes back on line, PCM will resume closed loop operation. On some vehicles, MIL will remain on until ignition is shut off and vehicle is restarted. To prevent damage to catalytic converter, vehicle should NOT be driven for extended periods in limp-in mode.

Dakota & Durango M/T Models

Using information supplied by A/C signal (if equipped), ECT sensor, and VSS, PCM controls operation of electric cooling fan. PCM operates fan through radiator fan relay by grounding or ungrounding relay control circuit. PCM regulates engine idle speed through IAC motor when fan is on.

Dakota & Durango

PCM provides ground for shift indicator light on models equipped with manual transmission. Based on engine speed, throttle position, and vehicle speed, PCM turns shift indicator light on to advise driver to shift to a higher gear for optimum fuel economy.

System is electrically actuated and vacuum operated. Controls are located on steering wheel. Controls consist of 3 buttons: OFF/ON, RESUME/ACCEL and SET/DECEL. Speed control servo is controlled by PCM. System will operate at 35-85 MPH.

PCM provides signal to drive tachometer.

TRANSMISSION GOVERNOR SOLENOID

PCM controls solenoid to regulate line pressure for shift control.

PCM controls indicator light on OD/OR switch on models equipped with overdrive automatic transmission.

On models equipped with OD transmission, PCM controls 3-4 OD upshift and downshift through OD solenoid. PCM determines optimum OD shift scheduling for all operating conditions.