Engine Controls - Theory & Operation: Other Dodge Intrepid II

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), tachometer (if equipped) and fuel pump. 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 and 8-volt outputs. The 5-volt output powers battery temperature sensor, Camshaft Position (CMP) sensor on some models equipped with Distributorless Ignition System (DIS) or distributor on some models without DIS, Crankshaft Position (CKP) sensor, Engine Coolant Temperature (ECT) sensor, Intake Air Temperature (IAT) sensor, logic circuits, Linear Exhaust Gas Recirculation (EGR) solenoid, Manifold Absolute Pressure (MAP) sensor, Throttle Position (TP) sensor, Output Speed Sensor (OSS) on some models or Vehicle Speed Sensor (VSS) on some models. The 8-volt output is used to power CMP sensor on some models with DIS or distributor on some models without DIS and CKP sensor. The 8-volt output may also be used to power VSS on some models.

PCM LOCATION

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 component circuits).

INPUT DEVICES

Note. To determine component location and input device usage on a specific model, see WIRING DIAGRAMS article.

Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. Available input signals include

A/C Pressure Sensor (All Models)

Sensor may also be referred to as A/C transducer or dual pressure switch. Sensor monitors A/C discharge (high-side) pressure. Sensor signals PCM when pressure is sufficient for A/C operation.

A/C Switch

Note. On Concorde, Intrepid, LHS and 300M Automatic Temperature Control (ATC) models, the A/C switch is incorporated in the automatic temperature control head.

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.

Ambient/Battery Temperature Sensor (2.5L Sebring Convertible)

PCM uses sensor to determine temperature of battery area 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

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

This switch may also be referred to as a stoplight switch. PCM uses this switch input to maintain idle speed at a scheduled 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 equipped with a distributor, CMP sensor is made up of a Hall Effect switch (sync signal generator) and a rotating pulse ring (shutter) on distributor shaft. (Scheme 1) On Distributorless Ignition System (DIS), CMP sensor reads slots in cam timing sprocket. 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)

CKP is a Hall Effect-type sensor. CKP sensor can be mounted on left rear side of transmission bellhousing, on right rear side of block, near cylinder head, or mounted to cylinder head, under distributor. Sensor reads slots on outer edge of flywheel/flexplate or on crankshaft counterweight. Each slot causes a pulse to be generated as it passes under CKP sensor. Signal generated provides engine speed and CKP information to PCM, which along with other input signals, determines fuel injection sequence, ignition signal and spark timing.

Cruise Control Switches

Cruise control switch provides PCM with 5 separate inputs. ON or OFF switch informs PCM that cruise control system has been activated. SET switch informs PCM that set vehicle speed has been selected. COAST switch will allow car to decelerate until switch is released. RESUME switch informs PCM that a previously set speed has been selected. ACCEL switch 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

Note. On some models, the fuel level sensor is located in fuel module assembly.

Sensor may also be referred to as fuel gauge sending unit. Sensor sends a variable voltage to PCM to indicate fuel level. PCM uses this input to prevent setting a misfire or fuel system monitor diagnostic trouble code if fuel level is less than about 15 percent of capacity.

Heated Oxygen Sensor (HO2S)

Note. Models are equipped with either 2 or 4 HO2S. Some federal emission vehicles will have 4 HO2S. See wiring diagram in WIRING DIAGRAMS article for vehicle information on upstream and/or downstream HO2S.

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. OBD II system uses a second HO2S after converter to monitor converter efficiency.

Ignition Switch

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 (IAT) Sensor (All Models)

Note. On Breeze, Cirrus and Stratus equipped with 2.0L engine, Concorde 3.2L, and Intrepid, LHS and 300M with 3.5L engine, IAT sensor and Manifold Absolute Pressure (MAP) sensor are combined in one unit.

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

Knock Sensor (Except 2.5L)

Knock sensor detects cylinder block vibrations caused by knocking and sends a signal to PCM. PCM retards ignition timing according to strength of knocking.

Manifold Absolute Pressure (MAP) Sensor (All Models)

Note. On Breeze, Cirrus and Stratus equipped with 2.0L engine, Concorde 3.2L, and Intrepid, LHS and 300M with 3.5L engine, MAP sensor and Intake Air Temperature (IAT) sensor are combined in one unit.

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.

Output Speed Sensor (Except 2.0L)

Models equipped with 4-speed A/T use a transmission OSS. OSS is located on output shaft of transaxle. OSS delivers input signal to Transmission Control Module (TCM), which in turn sends signal to Powertrain Control Module (PCM) to indicate transmission output shaft speed.

Park/Neutral (P/N) Switch

P/N switch may also be referred to as transmission range sensor or transmission range switch and 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 (All Models)

PSP switch sends a signal to PCM when power steering pressure (load) rises to more than a predetermined pressure. When power steering load is high, such as during parking, PCM increases engine idle speed through IAC motor to prevent stalling.

Sensor Return

Sensor return circuit provides ground reference for all sensors. Ground connection is inside PCM.

Serial Communication Interface (SCI) Receive

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 (TP) Sensor

TP sensor monitors opening angle of throttle blade. TP sensor will vary output voltage from about .5 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.

Vehicle Speed Sensor (Breeze, Cirrus, Neon & Stratus M/T Models)

Note. Models equipped with 4-speed A/T, Output Speed Sensor (OSS) supplies vehicle speed and distance inputs to PCM through TCM. See OUTPUT SPEED SENSOR .

Models equipped with M/T, Neon and some A/T equipped models, VSS generates a predetermined number of pulses per sensor revolution (4 pulses per revolution on some models, or 8 pulses per revolution on other models). VSS input is used by PCM to determine vehicle speed and distance traveled.

Speed and distance inputs along with TP sensor closed throttle input, determine if a closed throttle deceleration or normal throttle idle (vehicle stopped) condition exists. During deceleration, PCM controls IAC motor to maintain a desired MAP value. During idle (vehicle stopped), PCM controls IAC motor to maintain a desired idle speed.

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 and output usage on a specific model, see appropriate wiring diagram in 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.

Data Link Connector (DLC)

Serial data is output to DLC, located under left side of instrument panel.

Distributorless Ignition System (DIS)

See DISTRIBUTORLESS IGNITION SYSTEM (DIS) under IGNITION SYSTEM.

Electric EGR Transducer (EET)

See EXHAUST GAS RECIRCULATION (EGR) under EMISSION SYSTEMS.

Evaporative Canister Purge Control Solenoid (EVAP-CPCS)

See EVAPORATIVE (EVAP) EMISSIONS SYSTEM under EMISSION SYSTEMS.

Exhaust Gas Recirculation (EGR) Solenoid

See EXHAUST GAS RECIRCULATION (EGR) 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.

In-Tank Fuel Pump

See FUEL DELIVERY under FUEL SYSTEM.

Leak Detection Pump (LDP)

See EVAPORATIVE (EVAP) EMISSIONS SYSTEM under EMISSION SYSTEMS.

Limp-In Mode

See LIMP-IN MODE under MISCELLANEOUS CONTROLS.

Malfunction Indicator Light (MIL)

See MALFUNCTION INDICATOR LIGHT under SELF-DIAGNOSTIC SYSTEM.

Manifold Tuning Valve (MTV)

See MANIFOLD TUNING VALVE (MTV) under MISCELLANEOUS CONTROLS.

Proportional Purge Solenoid

See EVAPORATIVE CANISTER PURGE CONTROL SOLENOID (EVAP-CPCS) under EMISSIONS SYSTEMS.

Radiator Fan Relay

See RADIATOR FAN RELAY under MISCELLANEOUS CONTROLS.

Serial Communications Interface (SCI) Transmit

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

Short Runner Valve (SRV)

See SHORT RUNNER VALVE (SRV) under MISCELLANEOUS CONTROLS.

Speed Control Servo

See SPEED CONTROL SERVO under MISCELLANEOUS CONTROLS.

Tachometer

See TACHOMETER 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.

Regulator may be located outside fuel tank, between tank and rear of vehicle (Avenger and Sebring Coupe), or with in-tank fuel pump module (all others). On regulators located in fuel pump module, 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.

On all models except Avenger and Sebring Coupe, a 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 between intake manifold and fuel rails. 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 temperature (engine and ambient) by adjusting amount of air flowing through by-pass in 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, engine vacuum and engine RPM. During engine operation, PCM can supply an infinite number of advance curves to ensure proper engine operation.

Except 2.5L Models

Note. Vehicles with 2.5L engines are not equipped with DIS.

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. Some models use one coil per plug, some models use one coil to fire 2 paired spark plugs at the same time. In paired systems, one cylinder is on compression stroke and other cylinder is on exhaust stroke.

2.5L Models

Note. Only 2.5L models are equipped with Hall Effect ignition systems.

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. To determine component usage on a specific model, see appropriate EMISSION APPLICATIONS article.

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.

Evaporative Canister Purge Control Solenoid (EVAP-CPCS) - All Models

Note. Evaporative Canister Purge Control Solenoid (EVAP-CPCS) may also be referred to as proportional purge solenoid.

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. PCM controls vapor flow using solenoid.

Leak Detection Pump (LDP) - All Calif. & Northeastern State Models

On vehicles equipped with Calif. emissions, LDP incorporates 2 primary functions: it detects a leak in EVAP system, and it seals EVAP system so leak detection test can be run.

Primary LDP components are a 3-port solenoid that activates both primary functions, a pump with an LDP switch that monitors pump movement, 2 check valves and spring diaphragm, and a canister vent seal containing a spring-loaded vent seal valve.

Immediately after a cold start, with engine temperature between predetermined temperature threshold limits, 3-port solenoid is briefly energized allowing engine vacuum to enter pump and draw diaphragm up. This allows air to be drawn into LDP cavity. When solenoid is de-energized, it vents engine vacuum, permitting diaphragm to drop down, forcing air out of LDP. Repeated energizing and de-energizing cycles create flow in pump fashion.

After passing leak detection phase of test, system pressure is maintained until EVAP purge system is activated, creating an artificial leak. If cycle rate increases due to flow of EVAP purge system, LDP test passes. If LDP test does not pass, an obstruction exists in system.

EXHAUST GAS RECIRCULATION (EGR)

Note. Neon models are not equipped with EGR systems.

Except Neon

EGR system allows a predetermined amount of exhaust gas to enter cylinders with air/fuel mixture. This dilution of cylinder air/fuel volume reduces oxides of nitrogen (NOx) and helps prevent spark knock by reducing peak temperatures inside combustion chamber.

EGR system is a backpressure type and uses an Electric EGR Transducer (EET). (Scheme 4) This system incorporates backpressure transducer and EGR solenoid into one unit. Backpressure transducer measures amount of exhaust gas backpressure on exhaust side of EGR valve and varies amount of vacuum applied to EGR valve.

This system allows backpressure transducer to provide proper vacuum signal to EGR valve for all engine operating conditions. EGR system is controlled by an EGR vacuum solenoid using a manifold vacuum signal from throttle body.

Scheme 4

All Models

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.

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. Transaxle Range (TR) Sensor Transmits transaxle 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. Instrument Panel (I/P).
2. Body Control Module (BCM).
3. Air Bag System Diagnostic Module (ABSDM).
4. Full Automatic Temperature Control (ATC) display head.
5. Controller Anti-lock Brake (CAB).
6. Transmission Control Module (TCM).
7. Powertrain Control Module (PCM).
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) on some vehicles. 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 (DRBIII(R)). Problems with operation of bus or DRBIII(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 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 reset Service Reminder Indicator (SRI) light on some vehicles and 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.

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 DC current produced by generator. For additional information on charging system, see GENERATORS & REGULATORS - CARS 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.

2.7L, 3.2L & 3.5L

PCM controls MTV solenoid. MTV optimizes acoustical tuning of intake system during wide open throttle operation throughout RPM range. Valve opens a crossover passage connecting both sides of intake manifold plenum.

Note. All models use high and low speed radiator fan relays, except Neon which uses a single radiator fan relay.

Using information supplied by A/C signal, ECT sensor, transmission thermoswitch (A/T) and TP sensor, PCM controls operation of electric cooling fan. PCM operates fan through radiator fan relay by grounding relay circuit. PCM regulates engine idle speed through IAC motor when fan is on.

On models using multiple fan relays, one relay operates under normal (low speed) operation and the other relay works under high speed or extra load (A/C on) condition. Some models use more than one cooling fan. Second fan may function as an auxiliary cooling device when A/C is engaged or during periods of engine overheating, or high A/C refrigerant pressure.

3.2L & 3.5L

SRV system operates under wide open throttle conditions at more than 5000 RPM to maximize engine performance. PCM energizes SRV solenoid, allowing mechanical linkage to redirect intake airflow to 6 short runners. PCM looks for a current spike when actuating solenoid. If spike is not present, PCM sets a diagnostic trouble code.

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.