Engine Control System - Theory & Operation: Other Pontiac Vibe I

AIR INDUCTION SYSTEMS

The air induction system provides air with oxygen for the combustion process. The air cleaner keeps dirt from entering the engine. Outside air is drawn into the air cleaner lower assembly and passes through the air cleaner element. Next, the air enters the air cleaner upper assembly and flows past the Mass Air Flow (MAF) sensor. The air then flows through the duct, to the throttle body, and into the intake manifold. Finally the air travels into the cylinder head and through the intake port, ending in the combustion chamber. The air cleaner upper assembly contains MAF sensor and the auxiliary intake air control solenoid.

Auxiliary Intake Air Control System

The auxiliary intake air control solenoid is operated by the Powertrain Control Module (PCM). The PCM supplies a ground path to the solenoid control circuit using an internal solid state device called a driver. The auxiliary intake air control system supplies additional air to the engine during hard acceleration and when operating under high engine loads. The lower air cleaner housing has two inlet air ducts. The auxiliary inlet air duct is opened or closed by a vacuum operated door. Manifold vacuum is supplied to the door motor by a vacuum solenoid. When the PCM commands the solenoid ON, voltage on the control circuit should be near zero or low. When the PCM commands the solenoid OFF, voltage on the control circuit should be near battery voltage or high. When the solenoid is energized, manifold vacuum is applied to the vacuum motor and the auxiliary inlet air duct door is closed. (Scheme 4) For diagnosis of auxiliary intake air system refer to SYSTEM & COMPONENT TESTING - 1.8L VIBE article.

Scheme 4

COMPUTERIZED ENGINE CONTROLS

The computerized engine control system monitors and controls a variety of engine/vehicle functions. The computerized engine control system is primarily an emission control system which is designed to maintain a 14.7:1 air/fuel ratio under most operating conditions. When the ideal air/fuel ratio is maintained, the 3-way catalytic converter can control oxides of nitrogen (NOx), hydrocarbon (HC) and carbon monoxide (CO) emissions.

The computerized engine control system consists of the master controller (PCM or ECM), input devices (sensors and switches) and output signals.

POWERTRAIN CONTROL MODULE

For exact location of Powertrain Control Module (PCM), see COMPONENT LOCATIONS in SELF-DIAGNOSTICS - 1.8L VIBE article. PCM may also be referred to as an Electronic Control Module (ECM). Although the 2 units may process different signals, the 2 terms are interchangeable.

The Powertrain Control Module (PCM) is a precision 32-bit microprocessor and is an essential part of the electronic control system. The PCM is located below the Instrument Panel (IP) storage compartment. Communication with the PCM is through the data link connector located below left side, of the IP.

The PCM performs the OBD-II diagnostic tests of the emission related systems. The PCM supplies a buffered voltage, called reference voltage, to the various information sensors and switches. PCM controls most components with an electronic switch that completes a ground circuit when turned ON. The electronic switch is commonly referred to as an output driver. The PCM is also responsible for a self-diagnosis function and a fail-safe function. Battery positive voltage is supplied to the PCM even when the ignition switch is OFF. The battery positive voltage is used for the PCM keep alive memory and the air-fuel ratio adaptive control memory.

Fail-Safe Function

When a malfunction occurs within the engine control system, the PCM maintains control over the fuel injection system, idle speed control system, etc. PCM controls these systems by using calculated values and/or backup programs stored within the PCM. This function is called the fail-safe function. With the fail-safe function, a certain level of engine performance is available even when a malfunction occurs. The fail-safe function prevents a complete loss of engine performance. The systems covered by the fail-safe function are

1. Mass Air Flow (MAF) sensor.
2. Intake Air Temperature (IAT) sensor.
3. Throttle Position (TP) sensor.
4. HO2S heater circuits.
5. Knock Sensor (KS) system.
6. Central Processor Unit (CPU) in the PCM.
7. Fuel cut-off for ignition system failures.

Control Module Learning Ability

The Powertrain Control Module (PCM) has a learning ability which enables the control module to make corrections for minor variations in the fuel system. This learning ability can improve driveability. Disconnecting the battery resets the learning process. A change in the vehicle's performance may be noticed when a reset from a PCM power down occurs. Operating the vehicle under varying conditions will enable the control module to regain any lost vehicle performance. In order to initiate the control module learning ability, warm the engine to operating temperature and drive the vehicle at part throttle with moderate acceleration. Continue to drive the vehicle while including steady cruise and idle speed operation. For the best idle speed quality several key cycles with a short drive and long idle periods is recommended.

Check Mode

The Powertrain Control Module (PCM) has the ability to operate in the Normal mode or in the Check mode. The 2 modes of operation are similar. When the PCM is operating in the Check mode, PCM has an increased ability to detect malfunctions. The most significant feature of the Check mode operation is that all "B" type codes now run like "A" type codes. In order to request that the PCM operate in the Check mode, scan tool communication with the PCM is necessary.

PCM Output Controls

The Powertrain Control Module (PCM) can be directed by a scan tool to operate certain solenoids, valves, motors, and switches. This scan tool function is generally referred to as Output Controls. Output Controls can be found under SPECIAL FUNCTIONS selection of the scan tool. Some Output Controls may be disabled by the PCM during certain types of vehicle operation. Operating a PCM controlled device with the scan tool should be limited to a maximum of ten seconds per test period.

Electrical/Accessory Load Idle-Up Signal

The Powertrain Control Module (PCM) receives an idle-up signal when certain engine electrical loads or engine accessory loads are present. The PCM increases the flow of air through the idle (bypass) air passage of the Idle Air Control (IAC) valve when receiving an idle-up signal. The additional air flowing through the idle air passage causes an increase in the idle speed. The idle speed is increased in order to accommodate the increased engine electrical or engine accessory load. The PCM monitors the following systems for idle-up signals

1. Electric rear window defogger.
2. Exterior lighting system.
3. A/C system. When A/C is selected from the HVAC control unit the PCM receives a 12 volt signal. Once the PCM is aware of the request for A/C, PCM determines whether engagement of the A/C compressor clutch is okay. In order to enable compressor clutch engagement, PCM provides a ground for the control circuit of the A/C compressor clutch relay. The PCM also increases engine idle speed in order to prevent a rough idle or a stalling condition when the A/C compressor is engaged.
4. Power steering system. See «POWER STEERING PRESSURE SWITCH»(ref-152296-S23915747162003012700000) under INPUT DEVICES.

INPUT DEVICES

Note. Components are grouped into 2 categories. The first category covers INPUT DEVICES, which control or produce voltage signals monitored by the control unit. The second category covers OUTPUT SIGNALS, which are components controlled by the control unit.

The PCM supplies a buffered (reference) voltage to the various information sensors and switches. PCM monitors the input components for circuit continuity and out-of-range values. PCM also provides performance checking. Performance checking refers to the PCM indicating a fault when the signal from an input does not seem reasonable, i.e., a Throttle Position (TP) sensor that indicates a high throttle position at low engine loads or low manifold absolute pressure sensor voltage. The input components may include, but are not limited to the following sensors and switches

1. A/C compressor clutch relay (A/C relay).
2. Camshaft Position (CMP) sensor.
3. Crankshaft Position (CKP) sensor.
4. Engine Coolant Temperature (ECT) sensor.
5. Fuel Tank Pressure (FTP) sensor.
6. Heated Oxygen Sensor (HO2S).
7. Knock Sensor (KS).
8. Mass Air Flow (MAF) sensor.
9. Power Steering Pressure (PSP) switch, if equipped.
10. Transmission Range Switch (A/T only).
11. Throttle Position (TP) sensor.
12. Vehicle Speed Sensor (VSS).

A/C Compressor Clutch Relay

Pressing the A/C button enables the PCM to request A/C compressor engagement and illuminate the A/C indicator. The A/C button sends a signal to the PCM for A/C compressor engagement. The PCM will provide a ground for the A/C compressor clutch relay enabling it to close its internal contacts to send battery voltage to the A/C compressor clutch coil. The A/C compressor diode will prevent a voltage spike, resulting from the collapse of the magnetic field of the coil, from entering the vehicle electrical system when the compressor is disengaged. Defrost and Defog mode selections will request A/C operation but not turn on the A/C indicator. The blower switch must be in any position except OFF for the A/C system to operate. The A/C system can operate regardless of the temperature control setting. The following conditions must be met in order for the A/C compressor clutch to turn on

1. Ambient air temperature above 40°F (4°C).
2. A/C refrigerant pressure switch parameters are met.
3. PCM receives an A/C request from the A/C switch.
4. Engine coolant temperature is less than 250°F (121°C).
5. Engine speed is more than 550 RPM.
6. Throttle position is less than 100 percent.

A/C Pressure Sensor & Switch

The PCM monitors the A/C refrigerant pressure switch signal circuit. If the PCM detects a pressure signal out of parameters, it will disable the A/C request. This switch assists in cycling the A/C compressor and prevents A/C compressor operation if system has a low refrigerant level. The sensor information is used by the PCM to determine A/C system load on the engine and A/C system pressures. Once engaged, the compressor clutch will be disengaged for the following conditions

1. Ambient air temperature is less than 40°F (4°C).
2. Throttle position is 100 percent.
3. A/C high side pressure is more than 455 psi (3140 kPa).
4. A/C low side pressure is less than 28 psi (196 kPa).
5. Engine coolant temperature is more than 250°F (121°C).
6. Engine speed is more than 5500 RPM.
7. PCM detects insufficient idle quality.

The A/C refrigerant pressure switch prevents the A/C system from operating when an excessively high or excessively low pressure condition exists. The PCM enables the compressor clutch when A/C pressure is between 28-455 psi (196-3140 kPa). A/C refrigerant pressure switch can also ground the control circuit of the fan 2 relay, thereby switching the cooling fan from low speed to high speed. The switch is open below 178 psi (1226 kPa) and closed above 220 psi (1520 kPa). The change in fan speed improves the condenser's ability to lower refrigerant temperatures and pressures.

The PCM monitors the A/C refrigerant pressure switch signal circuit. If the PCM detects a pressure signal out of parameters, it will disable the A/C request. This switch assists in cycling the A/C compressor and prevents A/C compressor operation if system has a low refrigerant level. The sensor information is used by the PCM to determine A/C system load on the engine and A/C system pressures.

Once engaged, the compressor clutch will be disengaged for the following conditions

1. Ambient air temperature is less than 40°F (4°C).
2. Throttle position is 100 percent.
3. A/C high side pressure is more than 455 psi (3140 kPa).
4. A/C low side pressure is less than 28 psi (196 kPa).
5. Engine coolant temperature is more than 250°F (121°C).
6. Engine speed is more than 5500 RPM.
7. PCM detects insufficient idle quality.

A/C Evaporator Temperature Sensor

The PCM monitors the evaporator temperature sensor in order to detect a possible evaporator icing condition and to determine in-vehicle temperature. The PCM disables the compressor clutch if the temperature input does not correspond to a predetermined value.

Battery Voltage

Battery voltage is monitored by PCM. If battery voltage swings low, a weak spark or improper fuel control may result. To compensate for low battery voltage, PCM may increase idle speed, advance ignition timing, increase ignition dwell or enrich the air/fuel mixture. If voltage swings excessively high or low, PCM may set a charging system DTC and illuminate the charge indicator.

Brake Switch Feedback

Models equipped with cruise control systems may monitor the brake light switch circuit as well as the cruise control switch, Park/Neutral Position (PNP) switch (A/T) or Cruise Control Release Switch (M/T) to determine when to engage and disengage cruise control. Upon receiving a cancel signal, the cruise control de-energizes the magnetic clutch inside the cruise control servo. With the magnetic clutch de-energized, the servo and the connecting arm are no longer mechanically connected and the throttle returns to the idle position.

The brake light switch is located under the instrument panel directly above the brake pedal. When brake pedal is pressed, one set of brake light switch contacts close and a voltage signal is provided to the cruise control module. The cruise control module disengages cruise control system operation as soon as this voltage signal is sensed. When the brake pedal is pressed, another set of brake light switch contacts open, and the voltage circuit from the cruise control module to the magnetic clutch inside the servo is interrupted. With voltage removed from the magnetic clutch, the servos DC servo motor is disengaged from the worm gear and the throttle is permitted to return to the idle position. This feature is provided to ensure the cancellation of cruise control system operation during vehicle braking.

Camshaft Position Sensor

The Camshaft Position (CMP) sensor is located in the cylinder head near the number 4 fuel injector. The CMP sensor is a signal generator that is composed of a magnet and a coil with an iron core. The PCM relies on the AC signal provided by the CMP sensor in order perform the following

1. To optimize the ignition timing.
2. To optimize the fuel delivery.
3. To detect any engine misfire.
4. To monitor CMP actuator solenoid valve operation.

The CMP sensor signal rotor is part of the intake camshaft and has 3 teeth located on the outer circumference. When the CMP sensor signal rotor rotates past the CMP sensor, electrical signals are generated. The AC signals that are generated by the CMP sensor are sent to the PCM. The CMP sensor is also used to monitor engine misfire and monitor the operation of the CMP actuator system.

Scheme 5

Crankshaft Position Sensor

The Crankshaft Position (CKP) sensor is located in the front cover of the cylinder block near the crankshaft pulley. CKP sensor is a magnetic generator type sensor, producing an alternating current signal. The CKP sensor signal increases in both frequency and amplitude as the engine RPM increases. The CKP sensor sends this reference signal to the Powertrain Control Module (PCM) to indicate the crankshaft RPM and position. This reference signal is used by the PCM to calculate fuel injection pulse, establish Top Dead Center (TDC) for ignition timing and where to start ignition coil and injection sequencing. There will be no spark or fuel delivery if there is no CKP sensor signal. The PCM uses the CKP sensor signal along with the camshaft position (CMP) sensor signal for the following purposes

1. To calculate the fuel injector pulse.
2. To establish the piston position TDC for the ignition timing.
3. To start the ignition coil and fuel injection sequencing.

The CKP sensor reluctor has 34 teeth and is mounted on the crankshaft behind the timing chain cover and the crankshaft pulley. (Scheme 6) When the crankshaft rotates, the CKP sensor signal rotor teeth pass by the CKP sensor causing a fluctuation in the sensors magnetic field. The fluctuation in the magnetic field induces a voltage in the CKP sensor circuitry that corresponds to every 10 degrees of crankshaft rotation. The reluctor has one wide tooth that indicates TDC of the number 1 cylinder. With the information that the PCM receives from the CKP sensor, the PCM determines engine speed and crankshaft position.

Scheme 6

Engine Coolant Temperature Sensor

The Engine Coolant Temperature (ECT) sensor is a thermistor. A thermistor is a resistor whose value varies with the temperature. The electrical resistance of the ECT sensor is high when the coolant temperature is cold, and the resistance is low when the coolant temperature is warm. The ECT sensor is wired in series with a fixed resistor in the Powertrain Control Module (PCM). The PCM applies 5 volts to the ECT sensor. The PCM monitors the voltage across the ECT sensor and converts the voltage into a temperature reading. The voltage measured by the PCM will be high when the coolant temperature is cold, and low when the coolant temperature is warm.

Generator "L" Light Circuit (Charge Indicator)

The charge indicator is a LED located in the I/P cluster. It receives battery voltage when the ignition is in the RUN position. The circuit is grounded through the L terminal of the generator With the ignition ON, engine OFF, the generator will ground the generator "L" terminal circuit through a resistor when the regulator detects sense voltage below 9.5 volts or when no AC voltage is detected. When the engine is started and the generator begins to charge, the generator will open the circuit (still using the control voltage) signaling to the PCM that the generator is charging. If the voltage at the control module generator "L" terminal is low when the engine is running, the control module will send a message to the instrument panel cluster to illuminate the charge telltale.

Generator "F" Field Circuit

PCM monitors the duty cycle of the generator through the "F" circuit. As generator load increases, PCM can adjust idle speed accordingly.

Heated Oxygen Sensor

The HO2S produces a voltage that varies between 0.1-0.9 volt under normal operating conditions. The Powertrain Control Module (PCM) monitors this voltage and determines if the exhaust is lean or rich. If the voltage input at the PCM is about 0.1 volt the exhaust is lean, and if the voltage input is about 0.9 volt, the exhaust is rich. The PCM constantly monitors the HO2S 1 signal during closed loop operation and compensates for a rich or lean condition by decreasing or increasing the injector pulse width as necessary. Heated Oxygen Sensors (HO2S) are installed before (pre-catalyst) and after (post-catalyst) the TWC. Voltage variations between the sensors allow the PCM to determine the performance of the TWC catalyst. For more information, see CATALYST MONITOR DIAGNOSTIC OPERATION under SELF-DIAGNOSTIC SYSTEM.

Ignition/Crank Signal

The PCM monitors initial cranking (RPM) signal to determine when the engine is being started. This information is used for starting enrichment. If this signal is intermittent or not available, hard starting or a no-start condition will result.

Intake Air Temperature Sensor

The Intake Air Temperature (IAT) sensor is an integral part of the Mass Air Flow (MAF) sensor that is mounted in the air cleaner assembly. IAT sensor measures temperature of the air entering the intake manifold. IAT sensor provides temperature information to the circuitry of the MAF sensor and the PCM.

The IAT sensor is a thermistor, a resistor whose resistance changes as a function of temperature. When temperature is low, resistance is high. See IAT SENSOR OPERATION table. The resistance decreases as temperature increases. IAT sensor is a 2-wire circuit with a reference or signal voltage and a ground coming from the PCM.

IAT SENSOR OPERATION

Knock Sensor

The 1.8L engine is equipped with a flat design is non-resonant design Knock Sensor (KS) that is constructed of a piezoelectric element which generates an AC signal when vibrated. KS is located on the engine block behind the intake manifold, on the engine block between cylinders 2 and 3. Normal engine operation will cause the KS to generate signals of known frequencies. When engine knock is present, the KS frequency changes. This signals the Powertrain Control Module (PCM) to retard ignition timing. The PCM sends a bias voltage of 5 volts to the KS on the KS signal high circuit. The PCM expects approximately 2.5 volts back on the KS Signal Low circuit. The KS generated AC signal rides on top of the bias voltage provided by the PCM. The PCM uses the input from the KS to adjust the ignition timing in order to control detonation and enables the PCM to adjust the ignition timing in order to adapt to any of the variables that affect the optimal ignition timing. Ignition timing determines the relationship between the time the spark plug is fired and the time that the piston reaches top dead center (TDC). TDC is the point in time when the piston achieves maximum upward travel in the cylinder. If the spark plug ignites the compressed air/fuel mixture too late, not all of the air/fuel mixture has time to burn while the fuel is highly compressed. Late ignition causes a decrease in fuel efficiency, decreased power, and increased exhaust emissions. If the spark plug fires too soon, too much of the air/fuel mixture starts burning before the piston reaches the top of the compression stroke. Early ignition of the air/fuel mixture causes detonation, commonly referred to as spark knock. Constant spark knock in the motor is undesirable. Excessive spark knock can reduce engine performance. If severe enough, detonation can cause engine damage.

Every engine has an optimum ignition timing value. The optimum ignition timing is usually the earliest or most advanced firing of the spark plug that is possible without causing detonation. An engines optimum ignition timing is designed to be the most advanced ignition timing possible during the most demanding conditions. The optimum ignition timing is affected by all of the following variables

1. Engine load.
2. Engine temperature.
3. Atmospheric pressure.
4. Fuel quality.
5. Fuel's octane rating.

The KS detects when the engine is experiencing detonation. The sensor then signals the PCM to reduce the spark advance until detonation is no longer detected. A conventional resonant type KS uses a vibration plate that has the same resonance point as the expected knocking frequency of the engine. The non-resonant type KS has a steel weight with an insulator separating the weight from a piezoelectric element. (Scheme 7) The vibration caused by engine detonation is transferred to the weight, whose inertia applies pressure to the piezoelectric element. The weights action against the element, generates an electromotive force that is modified and transmitted to the PCM. The non-resonant design sensor is able to detect detonation vibration over a wide frequency band, from 6-15 kHz. In comparison, the resonant type KS detects only vibrations that are within a narrow frequency band.

In response to the KS signal, the PCM retards the spark advance in order to reduce the detonation. The amount of timing retard that the PCM applies is based on the engine speed and the length of time that the engine detonation is detected. Once the spark timing is retarded, the KS circuitry in the PCM performs calculations in order to determine how much spark advance should be re-introduced. Normally, the ignition timing advance is increased until zero retard, or normal ignition timing, is re-established. If detonation occurs again, the whole cycle will repeat. The alteration of the ignition timing by the KS often occurs continuously while the engine is running, even though no detonation is heard by the vehicle's operator.

Scheme 7

Loss of the KS signal causes the PCM to operate in fail safe mode. In fail safe mode the PCM commands maximum spark retard. A KS that falsely indicates detonation can cause the PCM to retard the ignition timing unnecessarily. Reduced spark advance can cause poor fuel economy, sluggish engine performance and/or higher exhaust emissions.

A KS that fails to detect detonation can cause the PCM to control the ignition timing as if no detonation were occurring. Failure of the PCM to retard the ignition timing when necessary could cause An excessive engine detonation, engine damage during heavy engine loads and/or higher exhaust emissions.

Mass Airflow Sensor

Note. MAF sensor also contains the Intake Air Temperature (IAT) sensor. IAT sensor cannot be serviced separately from the MAF sensor.

The Mass Air Flow (MAF) sensor measures changes in the intake air volume that result from changes in throttle opening and air density. Airflow measurements are used by the PCM in order to determine engine fueling requirements.

The MAF sensor is a hot-wire design. A platinum hot-wire and a thermistor are located in the intake air bypass passage of the MAF sensor housing. (Scheme 8) Temperature of the platinum hot-wire is affected by exposure to air flow and by exposure to air temperature. Platinum hot-wire is maintained at a set temperature by controlling the current flow through the wire. The MAF sensor converts changes in current flow to a voltage signal. The voltage signal from the MAF sensor enables the PCM to detect changes in air density and changes in air volume.

Scheme 8

Overdrive Off Indicator

With the ignition switch in the RUN position, voltage is applied through the Gage Fuse (10-amp) to the OD/OFF indicator light. Whenever the overdrive switch (located on the shifter) is released to the OFF position, system voltage is applied through the closed contacts of the overdrive switch to ground. When this occurs, the OD/OFF indicator light in the instrument cluster will illuminate and the Powertrain Control Module (PCM) will simultaneously receive a low voltage signal at the O/D ON/OFF input. With a low voltage input, the PCM will disable the overdrive function. Whenever the overdrive switch is depressed to the RUN position, the overdrive switch opens. When this occurs, the O/D/OFF indicator light in the instrument cluster will go out and the PCM will simultaneously receive a high voltage signal at the O/D ON/OFF input. With a high voltage input, the PCM will enable the overdrive function and the transaxle is permitted to shift into overdrive when appropriate.

Park/Neutral Position Switch

The Powertrain Control Module (PCM) determines when the vehicle is in Park or Neutral gear position through the Park/Neutral Position (PNP) switch. The Red/Black wire to the PCM is grounded by the PNP switch when the transmission manual selector is in either Park or Neutral gear position.

Power Steering Pressure Switch

The Power Steering Pressure (PSP) switch is normally open to ground. Turning the steering wheel increases the power steering oil pressure. Increased power steering oil pressure puts an additional load on the engine that may be noticeable at idle. The PSP switch closes when the power steering system oil pressure is high enough to cause an undesirable idle condition. The voltage signal from the PSP switch to the PCM indicates less than one volt when the PSP switch is closed. The voltage signal is near battery voltage when the PSP switch is open.

Rocker Arm Oil Pressure Switch

Rocker arm oil pressure switch detects oil pressure when the rocker arm oil control solenoid is ON. The oil pressure switch input enables the PCM to monitor the operation of the rocker arm oil control solenoid.

RPM Reference Signal

The RPM is monitored by PCM through tach/pulse signals produced by either the ignition control module or Crankshaft Position (CKP) sensor, Hall Effect signal, PM generator signal on DIS. These signals are used by the PCM for determining control of timing, fuel delivery, EGR function and idle speed.

Throttle Position Sensor

The Throttle Position (TP) sensor is a potentiometer connected to the throttle shaft on the throttle body. TP sensor is a potentiometer whose resistance value changes along with the throttle valve position. The Powertrain Control Module (PCM) provides a 5-volt reference voltage to the TP sensor. The PCM reads the voltage across the TP sensor and uses the voltage to calculate the percentage of throttle valve opening. Sensor resistance decreases as the throttle valve opening increases. When the TP sensor resistance decreases the voltage being monitored by the PCM increases. Sensor resistance increases when the throttle valve opening decreases, therefore the voltage being monitored by the PCM will decrease. At a closed throttle position, output of the TP sensor is low. As throttle valve opens, the output increases so that at wide open throttle, output voltage should be more than 3.3 volts.

Because position of the throttle valve controls the air supply to the engine, the PCM can modify the fuel delivery based on throttle angle. For example, power enrichment occurs when throttle angle approaches wide-open throttle. PCM looks primarily for changes in TP sensor output to control fuel delivery. Acceleration enrichment occurs when throttle angle increases, similar to the accelerator pump on a carburetor equipped vehicle.

Vehicle Speed Sensor

The Vehicle Speed Sensor (VSS) is mounted on the transaxle. As the transaxle turns the VSS, the VSS provides the speedometer with a vehicle speed input through voltage pulses. Each revolution of the axle shaft equals 4 pulses. This input is used to drive the speedometer. The speedometer converts the vehicle speed input to a more precise output which is sent to the Powertrain Control Module (PCM) and the cruise control module, if equipped. The PCM sends a 5-volt carrier signal to the speedometers vehicle speed output control circuit. On this same circuit, the speedometer produces a pulse width modulated signal that the PCM, and the cruise control module, use to determine the vehicle speed.

OUTPUT SIGNALS

The Powertrain Control Module (PCM) can be directed by a scan tool to operate certain solenoids, valves, motors, and switches. This scan tool function is generally referred to as output controls. The Output Controls can be found under SPECIAL FUNCTIONS menu of the scan tool. Some output controls may be disabled by the PCM during certain types of vehicle operation. Operating a PCM controlled device with the scan tool should be limited to a maximum of ten seconds per test period.

PCM is responsible for the control and operation of many output components. PCM controls many components with an electronic switch called an output driver that completes a ground circuit when turned ON. PCM monitors the output components for the proper response to the PCM commands. Components where functional monitoring is not feasible will be monitored for circuit continuity and out-of-range values if applicable. Output components to be monitored include, but are not limited to the following circuits.

A/C Compressor Clutch

See A/C COMPRESSOR CLUTCH under MISCELLANEOUS CONTROLS.

EVAP Canister Purge Valve

See EVAP CANISTER PURGE VALVE under EMISSION SYSTEMS & SUB SYSTEMS.

CMP Actuator Solenoid Valve

See CAMSHAFT POSITION ACTUATOR SOLENOID VALVE under INPUT DEVICES.

Cooling Fan Relay

See ELECTRIC COOLING FAN under MISCELLANEOUS CONTROLS.

Direct Ignition System

See IGNITION SYSTEMS .

Fuel Injectors

See FUEL INJECTORS under FUEL SYSTEMS.

Fuel Pump & Fuel Pump Relay

See FUEL DELIVERY under FUEL SYSTEMS.

Idle Air Control Valve

See IDLE AIR CONTROL VALVE under IDLE SPEED.

See KNOCK SENSOR under INPUT DEVICES.

Malfunction Indicator Light

See MALFUNCTION INDICATOR LIGHT under SELF-DIAGNOSTIC SYSTEM.

See POWER STEERING PRESSURE SWITCH under INPUT DEVICES.

Pressure Control Solenoid Valve (A/T)

PCM uses signals from the throttle position sensor to regulates the line pressure control solenoid by sending a predetermined duty ratio to the solenoid.

See POWER STEERING PRESSURE SWITCH under INPUT DEVICES.

Self-Diagnostics

See SELF-DIAGNOSTIC SYSTEM .

Serial Data

See SERIAL DATA under SELF-DIAGNOSTIC SYSTEM.

Shift Solenoids (Electronically-Controlled Transmission)

See TRANSMISSION under MISCELLANEOUS CONTROLS.

Fuel Tank

The fuel tank has a storage capacity of 49 liters (13 gallons). The tank is manufactured from steel and is located behind the rear seat area. The tank is held in place with bolts. The shape of this tank was designed to allow for a constant supply of fuel around the fuel pump strainer during low fuel conditions and also during aggressive vehicle maneuvers. The fuel inlet port on the tank is equipped with an inlet valve. This fuel tank inlet valve prevents the fuel from spewing into the fuel filler neck during aggressive vehicle maneuvers or vehicle rollovers. The fuel tank is equipped with an On-Board Refueling Vapor Recovery (ORVR) system. The fuel tank, pipes, and hoses should be checked for any road damage which could result in leakage. Also inspect the fuel filler cap for a correct seal and any indications of physical damage.

In order to prevent refueling with leaded fuel, the fuel filler neck has a built-in restrictor and deflector. The opening of the restrictor admits only the smaller unleaded fuel nozzle. The nozzle must be fully inserted to bypass the deflector. Any attempt at refueling with leaded fuel will result in fuel splashing out of the filler neck.

The fuel filler cap is a pressure-vacuum type. A built-in torque limiting device on the cap prevents overtightening and also eliminates the escape of fuel vapors. To install the cap, turn clockwise until a clicking noise is heard. This indicates that the fuel filler cap gasket is fully seated. A vacuum relief valve is incorporated into cap. If the pressure in the fuel tank becomes negative (vacuum), the relief valve opens to relieve the pressure created within the fuel tank. Only when vacuum becomes excessive within the tank does this occur. Vacuum pressure is also vented through the tank pressure control valve which is located on the top of the fuel tank. A pressure relief valve is also located in the fuel filler cap. The pressure of the fuel vapor within the tank should exceed that for which the fuel system is designed, the pressure relief valve opens, and the excess pressure is vented to the atmosphere.

Fuel Pump

The fuel pump is an electric pump controlled by the Powertrain Control Module (PCM) through the circuit opening relay. When PCM commands the fuel pump to operate, an impeller is driven by an electric motor in the pump assembly, causing the fuel in the tank to be drawn into the fuel pump inlet port. The fuel is then pumped under pressure through the fuel filter and the fuel pressure regulator, out to the fuel feed pipe and hoses to the fuel rail and the fuel injectors. The fuel pressure is maintained when the fuel pump is not running by a pressure control valve located within the pump. Any excess fuel is returned to the fuel tank by the fuel return pipe and hoses.

Fuel Pump Strainer

The fuel pump strainer attaches to the lower end of the fuel pump and reservoir assembly. The fuel pump strainer is made of woven plastic. The functions of the fuel pump strainer are to filter contaminants and to wick fuel. The fuel pump strainer is self-cleaning and normally requires no maintenance. Fuel stoppage at this point indicates that the fuel tank contains an abnormal amount of sediment or water.

Fuel Filter

The fuel filter located in the fuel tank and is part of the fuel sender assembly. The fuel filter housing is constructed to withstand the maximum fuel system pressure, exposure to fuel additives, and changes in temperature. The filter element is made of paper and is designed to trap the particles in the fuel that may cause damage to the fuel injection system.

Fuel Pressure Regulator

The fuel pressure regulator is located in the fuel tank and is part of the fuel sender assembly. The fuel pressure regulator is a diaphragm-operated pressure relief valve consisting of a diaphragm, a spring, and a valve. The fuel pressure regulator is inserted into the fuel sender assembly and sealed with an "O" ring. The fuel pressure regulator keeps the fuel delivered to the fuel injectors at the correct pressure.

System Voltage Compensation

A power supply system voltage drop will delay the mechanical operation of the fuel injector. The actual injector ON time becomes shorter when the system voltage decreases. In order to compensate for this, the fuel injector pulse width signal is lengthened.

Crank Signal

The crank signal is sent from the starter motor circuit. When the starter motor circuit is energized as the ignition switch is in the START position, a crank signal is supplied to the PCM. The PCM increases the fuel injector pulse when receiving a voltage on the crank signal circuit. The slight increase in fuel provides quicker and smoother engine start-up. The crank signal is also used as an input for running certain engine control system diagnostics, such as the CKP sensor DTC P0335. The crank signal input can be monitored on a scan tool as the Starter Switch parameter.

Base Air/Fuel Ratio Compensation

The base air/fuel ratio may vary due to differences in individual engines and mileage. In order to compensate for such variations, feedback information is used to adjust the base air/fuel mixture to maintain the optimum air/fuel ratio.

Fuel Cutoff

Fuel cutoff occurs when the PCM stops fuel injection or turns off the fuel pump. Fuel cutoff is used during the following conditions

1. During deceleration, when the throttle valve is closed and engine speed is high, fuel injection is stopped so that unburned gas will not be exhausted. Fuel injection starts again when the above conditions are no longer present.
2. In order to minimize any possible fuel spillage during an airbag deployment event, the fuel pump is de-energized. The PCM receives a signal from the Supplemental Inflatable Restraint (SIR) system and turns off the fuel pump relay. The relay is re-energized once the ignition switch is cycled off and then on again.

Fuel Metering System

The function of the fuel metering system is deliver the correct amount of fuel to the engine under all operating conditions. Fuel is delivered to each cylinder by the fuel injectors. The fuel injectors are controlled sequentially by the Powertrain Control Module (PCM). The PCM bases the control of the fuel injectors on several important engine parameters. These engine parameters include the following: Determining air density is critical to proper air/fuel management. Air density is primarily derived from the MAF sensor input.

The Mass Air Flow (MAF) sensor measures the air volume and determines the air density. Larger volumes of air and denser air masses require additional fuel. The information from the MAF sensor is used by the PCM in order to modify the fuel injector pulse width.

The fuel injector is an electromagnetic (solenoid) type injection nozzle which injects fuel into the intake port of the cylinder head according to the signals from the powertrain control module (PCM). There are 4 fuel injectors, one for each cylinder, located between the intake manifold and the fuel rail.

The PCM energizes the solenoid coil of the fuel injector, generating an electromagnet field that attracts the solenoid plunger. The needle valve, which is incorporated with the solenoid plunger, is opened by the movement of the solenoid plunger. The opening of the needle valve allows fuel that is under pressure to disperse thorough a four hole plate into a cone shaped pattern. Because the stroke of the needle valve in the fuel injector is set constant, the amount of fuel injected at one time is determined by the pulse width injection time (length of time the solenoid coil is energized).

Engine Starting Enrichment

In order to improve starting performance, fuel enrichment during start-up is carried out. For a certain time after the engine is started, the air/fuel mixture is enriched slightly in order to stabilize the engine speed. The amount of compensation varies depending on the engine coolant temperature as measured by the ECT sensor.

Engine Warm-Up Enrichment

During acceleration, the pulse of the fuel injectors is lengthened in order to deliver more fuel. The additional fuel required is relative to the engine coolant temperature. Acceleration Enrichment ensures smooth and reliable engine acceleration.

Power Enrichment

In order to provide maximum power during high engine load driving conditions, the air/fuel mixture is enriched when the throttle valve opening is more than a specified, PCM determined, value.

IDLE SPEED

The engine idle speed is controlled by the PCM through the Idle Air Control (IAC) valve. There are several reasons for idle speed control

1. In order to maintain the engine idle speed at the specified RPM at all times. The engine idle speed can vary due to any of the following reasons: A change in the load applied to engine such as when the rear defogger is operating, the automatic transaxle is shifted to R, D, 2 or L ranges, the A/C is turned ON, the headlights or stop lights are turned ON, etc. A change in the atmospheric pressure. A change in the engine's condition over time.
2. In order to improve the starting performance of the engine.
3. In order to improve the driveability of the engine during warm up.
4. In order to compensate for the change in the air/fuel mixture ratio when decelerating.

The Idle Air Control (IAC) valve is attached to the underside of the throttle body with 4 bolts. The IAC valve enables the Powertrain Control Module (PCM) to easily control the engine idle speed by precisely metering the engines air intake at closed throttle. IAC valve opens and closes the idle air bypass passage according to signals from the PCM. The IAC valve contains an engine coolant passage that enables the IAC valve to operate more efficiently at cold temperatures. PCM determines correct engine idle speed by using input from various sensors and switches in order to assess engine status and requirements.

PCM uses the IAC valve in order to control engine idle speed. PCM communicates with the IAC valve by varying the ON time of a repeating ON/OFF duty cycle. A magnet inside the IAC valve operates a rotary valve that controls the opening of idle air bypass passage in the throttle body. Idle air passage allows air to enter the engine without passing over the throttle valve. The strength of the magnet in the IAC valve is related to the current flow in the IAC circuit. PCM increases ON time of the IAC valve command in order to increase idle air passage opening. A larger idle air passage opening allows more air to enter the intake resulting in an increase in engine speed. IAC valve contains an engine coolant passage that enables the IAC valve to operate more efficiently at cold temperatures. IAC valve enables the PCM to easily control engine idle speed by precisely metering engine air intake at closed throttle.

IGNITION SYSTEMS

The electronic ignition system is of the Direct Ignition System (DIS) type and is controlled by the Powertrain Control Module (PCM). The electronic ignition system is composed of the following components

1. PCM.
2. 4 ignition coil assemblies.
3. Crankshaft Position (CKP) sensor.
4. Camshaft Position (CMP) sensor.
5. Spark plugs.

The electronic ignition system provides the following benefits

1. Improved ignition timing accuracy.
2. Reduced high-voltage losses.
3. Enhanced overall ignition system reliability.

The electronic ignition system components cannot be disassembled or repaired. A component that is correctly diagnosed as faulty must be replaced as a complete unit.

EMISSION SYSTEMS & SUB-SYSTEMS

Note. To determine emission system usage, see appropriate EMISSION APPLICATIONS article.

Three-Way Catalytic Converter

A Three-Way Catalytic Converter (TWC) is used on all vehicles to reduce exhaust emissions. This type of converter reduces hydrocarbon (HC), carbon monoxide (CO) and oxides of nitrogen (NOx) levels.

Converter contains a reducing agent (Rhodium and Platinum) to reduce NOx and an oxidizing agent (Palladium and Platinum) to oxidize HC and CO. This causes HC and CO to oxidize (combine with oxygen) into the harmless base elements: water (H2O) and carbon dioxide (CO2). Oxygen is removed from NOx, causing it to reduce to the harmless base elements nitrogen (N) and oxygen (O2).

EVAPORATIVE EMISSION CONTROL

The Evaporative Emission (EVAP) control system fuel vapors from escaping into the atmosphere. The fuel tank vapors are allowed to move from a sealed fuel tank, due to pressure in the tank, through a vapor pipe into the EVAP canister. Carbon in the canister absorbs and stores the fuel vapors. Excess pressure is vented through the vent line and vent valve to atmosphere. The EVAP canister stores the fuel vapors until the engine is able to use them.

At an appropriate time, the Powertrain Control Module (PCM) commands the purge valve ON, open allowing engine vacuum to be applied to the EVAP canister. With the EVAP vent valve OFF, open, fresh air will be drawn through the vent valve and vent line to the EVAP canister. The fresh air is drawn through the canister pulling fuel vapors from the carbon. The air/fuel vapor mixture continues through the purge pipe and purge valve into the intake manifold to be consumed during the normal combustion process.

Emissions laws require that the PCM detect any leakage within the EVAP system. The PCM monitors the EVAP system for leaks by controlling and observing the vapor pressures in the EVAP system. The FTP sensor is used to detect any unexpected pressure in the EVAP system. The PCM supplies a 5-volt reference and an electrical ground to the FTP sensor. The FTP sensor contains a silicon based chip that changes electrical resistance when pressure is applied. The sensor converts the positive or the negative pressure into an electrical signal and sends the signal to the PCM. See FTP SENSOR OPERATION table.

FTP SENSOR OPERATION

EVAP Canister

The EVAP canister is filled with carbon pellets used to absorb and store fuel vapors. Fuel vapors are stored in the EVAP canister until the PCM determines that the vapor can be consumed in the normal combustion process.

The EVAP canister purge valve controls the flow of fuel vapors from the EVAP system, to the intake manifold. The PCM will change the duty ratio cycle of the purge valve, controlling the purge flow volume. Purge flow volume is determined by manifold pressure, and the purge valves duty ratio cycle. Atmospheric pressure is allowed into the canister to ensure that purge flow is consistently maintained when ever purge vacuum is applied to the canister. The purge valve will also be opened during some portions of the EVAP system testing, allowing engine vacuum to enter the EVAP system.

EVAP Canister Vent Valve

The EVAP canister vent valve controls the flow of fresh air that passes through the EVAP canister. The vent valve is normally open. The PCM will command the EVAP canister vent valve closed during some EVAP tests, in order to seal the EVAP system for leak diagnosis.

EVAP Pressure Switching Solenoid

The EVAP pressure switching solenoid opens the evaporative line between the fuel tank and the EVAP canister. When the EVAP pressure switching solenoid is closed, air is blocked from entering the tank side of the system.

EVAP Service Port

The EVAP service port is located in the EVAP purge pipe, between the EVAP purge valve and the EVAP canister. The service port is identified by a Green colored cap.

Fuel Tank Pressure Sensor

The Fuel Tank Pressure (FTP) sensor, measures the difference between the fuel tank and outside air pressure. The PCM provides a 5-volt reference and a ground to the FTP sensor. The FTP sensor provides a signal voltage back to the PCM that can vary between 0.1 and 4.9 volts. As the fuel tank pressure increases, FTP sensor voltage decreases, as the fuel tank pressure decreases, FTP sensor voltage increases. High pressure equals high voltage. Low pressure vacuum equals low voltage.

Fill Limiter Vent Valve

The cross sectional view of the Fill Limiter Vent Valve (FLVV) shows the path of fuel vapors leaving the fuel tank by passing thorough the valve to the EVAP canister. (Scheme 9) When the fuel filler cap is removed during refueling, the atmosphere chamber fills with atmospheric pressure that has entered through the port from the fuel filler pipe. The pressure in the atmosphere chamber opens the port to the EVAP canister by closing the vent control valve. Refueling causes the internal pressure in the fuel tank to increase, pushing fuel vapors into the FLVV and out to the EVAP canister. When the fuel tank is full, the tank vapor control valve closes, sealing off the port to the EVAP canister.

Scheme 9

POSITIVE CRANKCASE VENTILATION

The Positive Crankcase Ventilation (PCV) system is used to provide more effective elimination of crankcase vapors. Fresh air from the air filter housing or throttle body is supplied to the crankcase where it is mixed with blow-by gases and passed through a PCV valve into the intake manifold. This mixture is then passed into the combustion chamber and burned.

The PCV valve provides primary control in this system by metering the flow of the blow-by vapors, according to manifold vacuum. When manifold vacuum is high (at idle), the PCV restricts the flow to maintain a smooth idle condition.

Under conditions in which abnormal amounts of blow-by gases are produced (such as worn cylinders or rings), the system is designed to allow the excess gases to flow back through crankcase vent hose into the intake or throttle body to be consumed during normal combustion.

Data Link Connector

Note. Do not use a scan tool that displays faulty data. Report the scan tool problem to the manufacturer. Use of a faulty scan tool can result in misdiagnosis and unnecessary parts replacement.

The provision for communicating with the control module is the Data Link Connector (DLC). The DLC is located under the instrument panel to the left of the steering column. The DLC is used to connect to a scan tool. Some common uses of the scan tool are listed as follows

1. Identifying stored Diagnostic Trouble Codes (DTC).
2. Clearing the DTCs.
3. Performing output control tests.
4. Reading the serial data.

As a bulb and system check, the Malfunction Indicator Light (MIL) will illuminate when ignition switch is turned to RUN position and engine is not running. When engine is started, MIL should go out. If MIL does not go out, a malfunction has been detected in the computerized engine control system or MIL circuit is faulty. To access codes, see SELF-DIAGNOSTICS - 1.8L VIBE article.

Catalyst Monitor (Good Catalyst)

A good TWC catalyst will show a very active output voltage on the pre-catalyst heated oxygen sensor. A good catalyst, 95 percent hydrocarbon conversion, will show a relatively flat output voltage on the post-catalyst heated oxygen sensor. (Scheme 10)

Catalyst Monitor (Bad Catalyst)

A degraded TWC catalyst, 65 percent hydrocarbon conversion, will show greatly increased activity in the output voltage from the post-catalyst heated oxygen sensor. The degraded catalyst post-catalyst HO2S output voltage will therefore appear similar to the typically active output voltage of the pre-catalyst heated oxygen sensor. (Scheme 11)

Scheme 10

Scheme 11

Conditions For Updating I/M System Status

Each system requires at least one, and sometimes several, diagnostic tests. The results of these tests are reported by a Diagnostic Trouble Code (DTC). A system monitor is complete when either all of the DTCs comprising the monitor have RUN and PASSED, or any one of the DTCs comprising the monitor have illuminated the Malfunction Indicator Light (MIL). Once all of the tests are completed, the I/M System Status display will indicate YES in the Completed column. For example, when the Heated Oxygen Sensor (HO2S) Heater Test indicates YES, all of the oxygen sensor heaters have been diagnosed. If the vehicle has four heated oxygen sensors, all four heater circuits have been diagnosed. The I/M System Status will indicate NO under the Completed column when any of the required tests for that system have not run. The following is a list of conditions that would set the I/M System Status indicator to NO

1. The vehicle is new from the factory and has not yet been driven through the necessary drive conditions to complete the tests.
2. The battery has been disconnected or discharged below operating voltage.
3. The control module power or ground has been interrupted.
4. The control module has been reprogrammed.
5. The control module DTCs have been cleared as part of a service procedure.

Monitored Emission Control Systems

The OBD-II System monitors all emission control systems that are on-board. Not all vehicles have a full complement of emission control systems. For example, a vehicle may not be equipped with secondary Air Injection (AIR) or Exhaust Gas Recirculation (EGR). The OBD-II regulations require monitoring of the following

1. Air conditioning system.
2. Catalytic converter efficiency.
3. Comprehensive component monitoring. Emission related inputs and outputs.
4. Evaporative (EVAP) emissions system.
5. Exhaust Gas Recirculation (EGR) system.
6. Fuel delivery system.
7. Heated catalyst monitoring.
8. Misfire monitoring.
9. Oxygen sensor (O2S or HO2S) system.
10. Oxygen sensor heater (HO2S heater) system.
11. Secondary Air Injection (AIR) system, if equipped.

For specific monitor information, see SELF-DIAGNOSTICS - 1.8L VIBE article.

PCM is equipped with a serial data line. Serial data is a stream of electrical impulses which can be interpreted by special testers or other control modules. When the ignition is turned on, each module sends a state of health message to the other modules using the serial data line. Ensuring the modules are working properly. If a module stops communicating, other control modules expecting information from that module will set a DTC. Serial data and codes must be accessed using a scan tool connected to the Data Link Connector (DLC). Update intervals and information contained within the data stream vary with model application.

CAMSHAFT ACTUATOR SYSTEM

The Camshaft Position (CMP) actuator system enables the Powertrain Control Module (PCM) to change camshaft timing while the engine is running. (Scheme 12) The CMP actuator assembly varies camshaft position in response to directional changes in oil pressure. The CMP actuator solenoid valve controls the oil pressure that is applied to advance or retard the camshaft. Modifying camshaft timing under changing engine demand provides better balance between the following performance concerns

1. Engine power output.
2. Fuel economy.
3. Lower tailpipe emissions.

The CMP actuator solenoid valve is controlled by the PCM. The Crankshaft Position (CKP) sensor and the CMP sensor are used to monitor changes in camshaft position. The PCM uses information from the following sensors in order to calculate the desired camshaft position

1. Engine Coolant Temperature (ECT) sensor.
2. Mass Air Flow (MAF) sensor.
3. Throttle Position (TP) sensor.
4. Vehicle Speed Sensor (VSS).

Scheme 12

CAMSHAFT POSITION ACTUATOR SOLENOID VALVE

The CMP actuator solenoid valve directs the oil flow that controls the camshaft phase movement. The PCM commands the CMP solenoid to move the solenoid plunger and spool valve until oil flows from the advance passage or the retard passage. In most operating conditions the opposite oil return passage is open at the same time as the oil supply passage. (Scheme 13)

Scheme 13

The PCM operates the CMP actuator solenoid valve by Pulse Width Modulation (PWM) of the solenoid coil. The higher the PWM duty cycle, the larger the change in camshaft timing. Oil pressure that is applied to the advance side of the fixed vanes will rotate the camshaft in a clockwise direction. The clockwise movement of the camshaft will advance the timing up to a maximum of 21 degrees. When oil pressure is applied to the return side of the vanes, the camshaft will rotate counterclockwise until returning to zero degrees.

CMP ACTUATOR SYSTEM ADVANCE

Oil flowing to the CMP actuator housing from the CMP solenoid advance passage applies pressure to the advance side of the vane wheel in the CMP actuator assembly. (Scheme 14) At the same time the CMP solenoid retard passage is open, allowing oil pressure to decrease on the retard side of the vane wheel. These two simultaneous actions cause the vane wheel to rotate clockwise, advancing camshaft advance timing.

Scheme 14

CMP ACTUATOR SYSTEM RETARD

When the oil flowing to the CMP actuator housing is from the CMP solenoid retard passage, oil pressure is applied to the retard side of the vane wheel. (Scheme 15) Because the solenoid advance passage is open, allowing oil pressure to decrease on the advance side of the vane wheel, the camshaft position retards.

The PCM can also command the CMP actuator solenoid valve to stop oil flow from both passages in order to hold the current camshaft position. The PCM is continuously comparing CMP sensor input with CKP sensor input in order to monitor camshaft position and detect any system malfunctions. The following table provides camshaft phase commands for common driving conditions. See CAMSHAFT PHASE COMMANDS table.

Scheme 15

CAMSHAFT PHASE COMMANDS

ROCKER ARM OIL CONTROL SYSTEM

The high output 1.8L (RPO-LNK) engine has a high speed cam system that increases engine output between 6000-8200 RPM. The increase in power is possible because valve lift is significantly increased at engine speeds above 6000 RPM. A second camshaft lobe with a high lift profile is cast into each camshaft, alongside the low/medium speed lobes. In order to use the high speed cam only when desired, the engine utilizes a rocker arm oil control system. The system uses unique rocker arms that are hydraulically operated and electronically controlled. (Scheme 16)

The rocker arms ride on rocker arm shafts that supply engine oil, that is under pressure, to the rocker arms. The flow of engine oil to the rocker arms and shafts is controlled by the rocker arm oil control solenoid valve. A rocker arm oil pressure switch signals the Powertrain Control Module (PCM) when oil pressure is detected. A screen type oil filter is located in the oil supply passage to the rocker arm shafts. The rocker arm oil control solenoid and the oil pressure switch are located in the oil control housing.

Scheme 16

During engine operation below 6000 RPM, the rocker arms follow the low/medium speed cam lobes. When engine oil is allowed to flow unobstructed to the rocker arms, the arms follow the high speed cam lobes, increasing valve lift. The flow of engine oil to the rocker arms is controlled by the rocker arm oil control solenoid valve. The solenoid is Pulse Width Modulated (PWM) by the PCM. The rocker arm oil pressure switch detects oil pressure when the rocker arm oil control solenoid is ON. The oil pressure switch input enables the PCM to monitor the operation of the rocker arm oil control solenoid. The rocker arm oil filter removes dirt and debris from the supply of engine oil to the rocker arm shafts.

The rocker arm oil control solenoid is commanded OFF by the PCM at engine speeds below 6000 RPM. With the solenoid OFF, oil that flows into the oil supply passage easily flows out thorough the solenoid and the return oil passage. (Scheme 17) There is adequate oil for lubrication of the rocker arms and shafts, but because the flow is unrestricted there is no increase in oil pressure. Without significant oil pressure in the rocker arms the low/medium speed cam followers operate the valve train. The rocker arm oil pressure switch is closed.

The rocker arm oil control solenoid is commanded ON by the PCM at engine speeds above 6000 RPM. With the solenoid ON, oil that flows into the oil supply passage is blocked by the solenoid from the return oil passage. (Scheme 18) This creates significant oil flow to the rocker shafts and the rocker arms. Oil pressure increases in the rocker arms and the high speed cam followers operate the valve train. The rocker arm oil pressure switch is open.

Scheme 17

Scheme 18

MISCELLANEOUS CONTROLS

Note. Although not considered true engine performance-related systems, some controlled devices may affect driveability if they malfunction.

On many models, PCM regulates operation of A/C compressor clutch through a PCM-controlled A/C compressor clutch relay. This allows the PCM to disengage the A/C compressor when compressor load on engine may cause driveability problems (i.e., during hot restart, idle, low speed steering maneuvers and wide open throttle operation), or if A/C refrigerant pressure drops or rises beyond normal operating levels.

Refrigerant pressure sensing may be accomplished by monitoring high and low pressure switches or a pressure sensor which will register either high or low pressure levels. Hot restart is monitored through the coolant temperature sensor. For component application and related wiring, see appropriate A/C COMPRESSOR CLUTCH CONTROLS - 1.8L VIBE article in AIR CONDITIONING & HEATING.

ELECTRIC COOLING FAN

The engine cooling fan system consists of an electric cooling fan, two fan relays and a fan resistor. The fan 1 relay controls power to the fan motor. The fan 2 relay controls the ground path of the fan motor. The gauge fuse supplies ignition voltage to the coils of both the fan 1, and the fan 2 relays. The RDI fuse supplies battery voltage to the switch side of the fan 1 relay. The PCM controls the ground for the coils of both relays. The PCM controls low and high speed fan operation by energizing and de-energizing the fan 2 relay which changes the ground path of the fan motor.

During low speed operation, which is when the A/C is operating and the Engine Coolant Temperature (ECT) is below 181°F (83°C), the PCM supplies the ground path for the fan 1 relay through the cooling fan 1 relay control circuit. This energizes the relay, closes the fan 1 relay contacts, and supplies battery voltage from the RDI fuse through the cooling fan motor supply voltage circuit to the fan motor. The ground path for the fan motor is through the closed contacts of the de-energized fan 2 relay, through the fan resistor to ground point G103. The result is a series circuit with the fan running at low speed.

During high speed operation, which is when the ECT reaches 199°F (93°C) or the A/C system pressure exceeds 220 psi (1520 kPa), the PCM supplies the ground path for the fan 1 relay through the cooling fan 1 relay control circuit. This energizes the relay, closes the fan 1 relay contacts, and supplies battery voltage from the RDI fuse through the cooling fan motor supply voltage circuit to the fan motor. The PCM also supplies the ground path for the fan 2 relay. This energizes the relay, switches the fan 2 relay contacts, and supplies a ground for the fan motor directly to ground point G103. The result is a series circuit with the fan running at high speed.

The A/C refrigerant pressure switch is in parallel with the PCM controlled ground for the coil of the fan 2 relay. If the A/C system pressure exceeds 220 psi (1520 kPa), the pressure switch closes the ground circuit to the coil of the fan 2 relay, initiating high speed fan operation.

The PCM commands low speed fan operation when all of the following conditions occur

1. A/C system is operating.
2. A/C system pressure is below 178 psi (1226 kPa).
3. Engine Coolant Temperature (ECT) is below 181°F (83°C).

The PCM commands high speed fan operation when either of the following conditions occur

1. ECT reaches 199°F (93°C).
2. A/C system pressure exceeds 220 psi (1520 kPa).

For component application and related wiring, see ELECTRIC COOLING FANS - 1.8L VIBE article in ENGINE COOLING.

Electronic Transaxle

The transaxle is controlled by the Powertrain Control Module (PCM). PCM controls other vehicle functions as well as the transmission. The PCM controls shift points by means of two shift solenoids. A third solenoid controls the application of the Torque Converter Clutch. A gear driven oil pump supplies the oil pressure. The PCM regulates oil pressure by means of a pressure control solenoid valve.

1. Shift Solenoid No. 1 Shift solenoid No. 1 and shift solenoid No. 2 are used together to electronically control the shifting of the transaxle from 1st gear to 4th gear/overdrive. The PCM outputs system voltage to turn ON (energize) or remove voltage to turn OFF (de-energize) either solenoid when it deems necessary. The transaxle shifts with the combination of both solenoids being turned ON and OFF. Shift solenoid No. 1 is normally ON in 1st and 2nd gears and never ON in 3rd or 4th gears. Shift solenoid No. 2 is normally ON in 2nd and 3rd gears and never ON in 1st or 4th gears. 4th gear/overdrive is obtained when both shift solenoids are OFF.
2. Shift Solenoid No. 2 Shift solenoid No. 2 is energized and de-energized by the PCM in response to varying transaxle shift demands. With the shift solenoid No. 2 de-energized, line pressure is applied to the 1-2 shift valve. With the line pressure applied, the 1-2 shift operates, and the transaxle shifts from second to third gear. When the PCM energizes the shift solenoid No. 1, line pressure is relieved, and the 1-2 shift valve does not operate.
3. Pressure Control Solenoid Pressure Control (PC) solenoid is attached to the valve body and controls line pressure by moving a pressure regulator valve against spring pressure. PCM varies line pressure based upon engine load. Engine load is calculated from several inputs including Manifold Absolute Pressure (MAP) sensor, Transmission Fluid Temperature (TFT) sensor, Throttle Position (TP) sensor and gear position. Line pressure is actually varied by changing the amperage applied to pressure control solenoid from .02 (maximum pressure) to 1.1 amps (minimum pressure). The PCM continuously varies the PC solenoid valve amps to maintain the correct average current flowing through the valve.