Engine Control System - 1.8L (Lnk) - Introduction: Other Pontiac Vibe I рестайлинг

Temperature vs Resistance

Temperature vs Resistance

Altitude vs Barometric Pressure

Altitude vs Barometric Pressure

Emissions Related DTCs

Action Taken When the DTC Sets - Type A

1. The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

Action Taken When the DTC Sets - Type B

1. The control module illuminates the MIL on the second consecutive ignition cycle that the diagnostic runs and fails.
2. When the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame/Failure Records.

Conditions for Clearing the MIL/DTC - Type A or Type B

1. The control module turns OFF the MIL after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC Last Test Failed clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Use a scan tool in order to clear the MIL and the DTC.

Non-Emissions Related DTCs

Action Taken When the DTC Sets - Type C

1. The control module stores the DTC information into memory when the diagnostic runs and fails.
2. The MIL will not illuminate.
3. The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
4. The driver information center, if equipped, may display a message.

Conditions for Clearing the DTC - Type C

1. A last test failed, or current DTC, clears when the diagnostic runs and passes.
2. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
3. Use a scan tool in order to clear the DTC.

Fuel Pressure Relief Procedure

Note. Do not perform this procedure if the engine is hot. Unburned fuel entering the catalytic converter could damage the converter catalyst.

1. Loosen the fuel filler cap in order to relieve the fuel tank pressure.
2. Remove the instrument panel (IP) storage compartment. Refer to «Storage Compartment Replacement - Instrument Panel (I/P)»(ref-200060-S30804947772005102000000) in Instrument Panel, Gages, and Console.
3. Reach in through the IP storage compartment opening and remove the circuit opening relay (1) from the fuse block IP (2).
4. Crank the engine and allow the engine to stall.
5. Crank the engine for an additional 3 seconds in order to assure relief of any remaining fuel pressure.
6. Disconnect the negative battery cable in order to avoid re-pressurizing the fuel system.
7. Install the circuit opening relay (1) into the fuse block IP (2).
8. Install the IP storage compartment. Refer to «Storage Compartment Replacement - Instrument Panel (I/P)»(ref-200060-S30804947772005102000000) in Instrument Panel, Gages, and Console.
9. Tighten the fuel filler cap.

Tools Required

1. J 34730-1A Fuel Pressure Gage. See «Special Tools»(ref-200095-S21125557472005102000000) .
2. J 42982 Fuel Pressure Gage Adapter. See «Special Tools»(ref-200095-S21125557472005102000000) .
3. J 43178 Fuel Line Disconnect Tool. See «Special Tools»(ref-200095-S21125557472005102000000) .

J 43178 Fuel Line Disconnect Tool. See Special Tools .

CH-47717 Fuel Lock Ring Remover Tool. See Special Tools .

Fuel System Cleaning

1. Disconnect the negative battery cable.
2. Remove the fuel tank from the vehicle. Refer to «Fuel Tank Replacement»(ref-200095-S01850779682005102000000) .
3. Remove the fuel sender assembly from the fuel tank. Refer to «Fuel Sender Assembly Replacement»(ref-200095-S34480041992005102000000) .
4. Fill the fuel tank with hot water.
5. Shake the fuel tank vigorously for 5 minutes.
6. Drain the fuel tank.
7. Inspect that all of the water is removed from the fuel tank.
8. Install the fuel sender assembly to the fuel tank. Refer to «Fuel Sender Assembly Replacement»(ref-200095-S34480041992005102000000) .
9. Install the fuel tank to the vehicle. Refer to «Fuel Tank Replacement»(ref-200095-S01850779682005102000000) .
10. Refill the fuel tank.
11. Connect the negative battery cable.
12. Inspect for fuel leaks and repair as necessary.

J 43178 Fuel Line Disconnect Tool. See Special Tools .

J 43178 Fuel Line Disconnect Tool. See Special Tools .

Control Module Learning Ability

The powertrain control module 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 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, the 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. For information on the use of the Check Mode in diagnosing driveability concerns, refer to Service Bay Test .

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. The 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.

Scheme 174

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 below

1. Identifying stored diagnostic trouble codes (DTCs)
2. Clearing the DTCs
3. Performing output control tests
4. Reading the serial data

Aftermarket (Add-On) Electrical and Vacuum Equipment

Note. Connect any add-on electrically operated equipment to the vehicle's electrical system at the battery (power and ground) in order to prevent damage to the vehicle.

Note. Do not attach add-on vacuum operated equipment to this vehicle. The use of add-on vacuum equipment may result in damage to vehicle components or systems.

Aftermarket (add-on) electrical and vacuum equipment is defined as any equipment installed on a vehicle after leaving the factory that connects to the vehicles electrical or vacuum systems. No allowances have been made in the vehicle design for addition of this type of equipment.

Add-on electrical equipment may cause the engine control system to malfunction even when the add-on electrical equipment is installed properly. Portable telephones and radios may also cause engine control system malfunctions even when not connected to the vehicles electrical system. The first step in diagnosing any engine control system problem is to remove all aftermarket electrical equipment from the vehicle. Diagnosis may proceed in the normal manner after eliminating aftermarket equipment as a cause of the engine control system malfunction.

Electrostatic Discharge (ESD) Damage

Note. In order to prevent possible Electrostatic Discharge damage to the PCM, Do Not touch the connector pins or the soldered components on the circuit board.

Electronic components used in the engine control system are often designed to operate at very low voltages. Electronic components are susceptible to damage caused by electrostatic discharge. Less than 100 volts of static electricity can cause damage to some of the electronic components. There are several ways for a person to become statically charged. The most common methods of charging are by friction and by induction. An example of charging by friction is a person sliding across a car seat. Charging by induction occurs when a person with well insulated shoes stands near a highly charged object and momentarily touches ground. Charges of the same polarity are drained off leaving the person highly charged with the opposite polarity. Therefore, use care when handling and testing electronic components in order to avoid electrostatic charges that can cause electronic component damage.

Input Components

The PCM supplies a buffered (reference) voltage to the various information sensors and switches. The PCM monitors the input components for circuit continuity and out-of-range values. The 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. The crankshaft position (CKP) sensor
2. The throttle position (TP) sensor
3. The engine coolant temperature (ECT) sensor
4. The camshaft position (CMP) sensor
5. The mass air flow (MAF) sensor
6. The heated oxygen sensor (HO2S)
7. The fuel tank pressure (FTP) sensor
8. The knock sensor (KS)
9. The vehicle speed sensor (VSS)
10. The rocker arm oil pressure switch
11. The power steering pressure (PSP) switch, if equipped
12. The transmission range switch (A/T only)
13. The A/C compressor control module (A/C relay)

Output Components

The PCM is responsible for the control and operation of many output components. The PCM controls many components with an electronic switch called an output driver that completes a ground circuit when turned ON. The 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

1. The idle air control (IAC) valve
2. The CMP actuator solenoid valve
3. The rocker arm oil control solenoid valve
4. The circuit opening relay
5. The evaporative emission (EVAP) system solenoids
6. The auxiliary intake air control solenoid
7. The malfunction indicator lamp (MIL) control
8. The A/C compressor control module (A/C relay)
9. The electronic transaxle controls

Fuel Tank

The fuel tank is a composite design with a storage capacity of 49 liters (13 gallons). The composite construction is made of several layers of materials. The outside and inside layers are a high density polyethylene, with a center layer of recycled material and ethylene vinyl alcohol copolymer. The fuel tank is located behind the rear seat area. The tank is held in place with two straps that are secured 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.

Fuel Tank Filler Neck

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.

Scheme 175

Note. If a fuel tank filler pipe cap requires replacement, use only a fuel tank filler pipe cap with the same features. Failure to use the correct fuel tank filler pipe cap can result in a serious malfunction of the fuel system.

The fuel filler cap used with the composite design fuel tank is an interrupted thread design (1). This type of cap requires only one quarter turn in order to seal the fuel system. A built-in torque limiting device on the cap prevents overtightening and also eliminates the escape of fuel vapors. To install the cap, turn the cap clockwise until a clicking noise is heard. This indicates that the fuel filler cap gasket (2) is fully seated.

A vacuum relief valve is incorporated into the fuel filler 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 the 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 that is controlled by the powertrain control module (PCM) through the circuit opening relay. When the 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.

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. Clean the fuel tank and replace a plugged fuel pump strainer with a new strainer.

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.

Scheme 176

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 one or more o-rings (1). The fuel pressure regulator used with the composite fuel tank is a double o-ring (3) design. A correctly calibrated fuel pressure regulator ensures that the fuel is delivered to the fuel injectors at the correct pressure.

Quick Connect Fittings

Quick connect style fuel fittings provide a simplified means of installing and connecting the fuel system components. Depending on the vehicle model, there are several types of quick connect fittings. Different types of fittings are used at different locations in the fuel system. Each type of quick connect fitting consists of a unique female connector and a compatible male fuel pipe end. O-rings located inside of the female connector provide a leak proof seal. Integral locking tabs or fingers hold the quick connect fittings together. A special tool is used to service some of the quick connect fittings.

Fuel Feed Pipes and Hoses

The fuel feed and return pipes and hoses carry the fuel from the fuel tank to the fuel injectors. These pipes and hoses are attached to the underbody of the vehicle and should be inspected periodically for kinks or dents that could restrict the fuel flow.

Fuel Vapor Pipes and Hoses

The fuel vapor pipe and hoses carry the fuel vapors from the fuel tank to the evaporative emission (EVAP) canister located at the rear of the vehicle, ahead of the fuel tank. The fuel vapors are stored in the canister when the engine is not running. When the engine is running at the normal operating temperature and the accelerator pedal is depressed, the PCM will command the EVAP canister purge valve to open and allow the stored fuel vapors to be purged into the intake manifold where the vapors will be burned in the combustion process.

Scheme 177

The on-board refueling vapor recovery (ORVR) system is an on-board vehicle system designed to recover fuel vapors during the vehicle refueling operation. Instead of allowing fuel vapors to escape to the atmosphere the ORVR system transports the vapor to the EVAP canister for use by the engine. The flow of liquid fuel down the fuel filler neck provides a liquid seal that prevents fuel vapor from leaving the fuel system. The ORVR system architecture varies from platform to platform. Some of the items listed below are optional depending on the platform application. The following is a list of all the ORVR system components with a brief description of their operation

1. The EVAP canister (1). The EVAP canister receives and stores refueling vapor from the fuel system. The EVAP canister releases the fuel vapor to the engine through the EVAP control system.
2. The vapor lines (2). The vapor lines transport fuel vapor from the fuel tank assembly to the EVAP canister.
3. The vapor recirculation line (3), if equipped. The vapor recirculation line transports fuel vapor from the fuel tank to the top of the fuel filler pipe during refueling in order to reduce the fuel vapor at the canister. The vapor recirculation line can be located inside the fuel filler pipe or outside of the fuel filler pipe.
4. The variable orifice valve (4), if equipped. The variable orifice valve regulates the amount of vapor allowed to enter the vapor recirculation line.
5. The fuel filler pipe (5). The fuel filler pipe carries fuel from the fuel dispensing nozzle to the fuel tank.
6. The check valve (6). The check valve limits fuel spitback from the fuel tank during the refueling operation by allowing fuel flow only into the fuel tank. The check valve is located at the bottom of the fuel filler pipe or in the fuel tank filler neck.
7. The fuel sender assembly (7). The fuel sender assembly pumps fuel to the engine from the fuel tank.
8. The fill limiter vent valve (8). The fill limiter vent valve is typically located in the fuel tank and acts as a shut-off valve. The fill limiter vent valve performs the following functions: Controls the fuel tank fill level by closing the primary vent of the fuel tank. Prevents liquid fuel from exiting the fuel tank through the vapor line and entering the EVAP canister. Provides fuel-spillage protection in the event of a vehicle rollover by closing the vapor path from the tank to the EVAP canister.
9. The pressure/vacuum relief valve (9), if equipped. The pressure/vacuum relief valve provides venting of excessive fuel tank pressure or vacuum. The pressure/vacuum relief valve is located in the fuel filler neck on a plastic fuel tank and in the fill limiter vent valve on a steel fuel tank.

Scheme 178

The fill limiter vent valve (FLVV) (1) is an integral part of the EVAP canister (3). The cross sectional view shows the path of fuel vapors passing through the valve directly into the EVAP canister. When the fuel filler cap is removed during refueling, the atmosphere chamber (2) fills with atmospheric pressure that has entered through the port from the fuel filler pipe. The pressure in the atmosphere chamber (2) opens the passage to the vapor chamber (5) by opening the vent control valve (6). Refueling causes the internal pressure in the fuel tank to increase, pushing fuel vapors into the ORVR port (4) and up through the vent control valve (6) into the EVAP canister (3). When the fuel tank is full, the tank vapor control valve (5) closes, sealing off the passage into the EVAP canister.

Accelerator Controls

The accelerator control system is cable-operated. When the accelerator pedal is depressed the cable pulls the throttle lever open, increasing the throttle plate opening, and when the accelerator pedal is released, the throttle lever spring pressure returns the throttle lever to the idle position, decreasing the throttle plate opening.

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

1. Engine speed (RPM)
2. Mass air flow (MAF)
3. Engine coolant temperature (ECT)
4. Intake air temperature (IAT)
5. Throttle Position (TP)
6. Fuel control oxygen sensor input (HO2S 1)

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.

Scheme 179

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 through a twelve 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-the length of time the solenoid coil is energized.

Synchronous Injection

When starting the engine, the fuel injectors inject the fuel simultaneously and synchronously at every camshaft position (CMP) sensor signal. When the engine is starting at a cold state, the amount of fuel is determined by the engine coolant temperature (ECT) sensor and is divided and injected.

Once the engine is running, the fuel injection occurs in a cylinder only when the cylinder is in the exhaust stroke. The PCM detects the compression stroke of cylinder 1 through the CMP sensor signal.

Asynchronous Injection

Whenever a change in the throttle valve opening exceeds a specified value, as determined by the PCM, additional fuel is injected simultaneously into the cylinders which are in the intake and exhaust strokes. This is in addition to the above synchronous injection and is not based on the ignition signal.

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

When the engine is cold, additional fuel is added in order to ensure good driveability. The level of enrichment of the air/fuel mixture is gradually decreased until the engine coolant temperature (ECT) sensor reaches a specified value.

Acceleration 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.

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 engine speed decreases to less than 1,400 RPM.
2. In order to prevent engine overrun, which adversely affects the engine, fuel injector delivery stops when the engine speed exceeds 8,500 RPM. Fuel delivery starts again when the engine speed decreases to a safe operating level.
3. 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.

EVAP System Function

The evaporative emission (EVAP) control system limits 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.

EVAP System Components

The EVAP control system consists of the following components

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.

EVAP Canister Purge Solenoid Valve

The EVAP canister purge valve controls the flow of fuel vapors from the EVAP system to the intake manifold. The purge solenoid valve is low side controlled by the PCM, using a pulse width modulated (PWM) or duty cycle circuit. The purge solenoid valve is also opened during some portions of the EVAP system testing.

Scheme 180

The EVAP vacuum leak pump assembly contains the fuel tank pressure (FTP) sensor, the canister vent solenoid, and an electric motor driven vacuum pump. The vacuum pump provides pressure for leak testing when the engine has been OFF for approximately five hours. The pump assembly also has several internal filters and a 0.5 mm (0.020 inch) reference orifice. The reference orifice provides controlled movement of the pressure within the system, enabling the FTP sensor to accurately monitor system performance. The complete pump assembly is mounted on the EVAP canister, eliminating the need for additional hoses or lines for connections.

EVAP Vacuum Leak Pump

The vacuum pump is driven by a 12 volt brush less motor that is high side controlled by the PCM. The pump is a vane type design capable of producing at least 33.50 mm Hg (18 in H2O) of vacuum pressure.

Scheme 181

The EVAP canister vent valve is an integral part of the EVAP vacuum leak pump assembly (2). The vent valve controls the flow of clean air into or out of (3) the EVAP canister. The vent valve is normally open. Under certain conditions the PCM commands the vent valve closed in order to seal the EVAP system for leak diagnosis.

Fuel Tank Pressure (FTP) Sensor

The fuel tank pressure (FTP) sensor, measures the difference between the fuel tank and outside air pressure. The FTP sensor is an integral part of the EVAP vacuum leak pump assembly. 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, the FTP sensor voltage decreases, as the fuel tank pressure decreases the FTP sensor voltage increases. High pressure = high voltage. Low pressure vacuum = low voltage.

Evaporative Emission (EVAP) Control System Description Chart

Scheme 182

The EVAP filter (1) is attached to the EVAP canister and provides clean air for the purging of fuel vapors. Excess pressure in the EVAP system also flows through the EVAP filter and is released into the atmosphere. The filter element is a sealed unit and is not serviceable separately.

EVAP Service Port

The EVAP service port is located underhood in the EVAP purge line, between the EVAP purge solenoid valve and the EVAP canister. The service port is identified by a green colored cap.

Scheme 183

During normal EVAP system operation the EVAP canister vent valve (4) is OPEN allowing the flow of fresh air (2) into the EVAP canister. If the EVAP canister purge valve is also OPEN, the fresh air will mix with vapors stored in the canister and flow (1) from the canister to the intake manifold. The FTP sensor (7) is used to monitor system operation and the vacuum leak pump (8) provides vacuum pressure for leak detection.

The PCM performs several diagnostic tests in order to determine if the EVAP system is functioning correctly or leaking. When certain operating criteria are met before engine shutdown, the PCM will run a comprehensive series of tests when the following conditions are met

1. Five hours have elapsed after the engine was turned Off
2. Altitude is less than 2,400 meters (8,000 feet)
3. Battery voltage is more than 10.5 volts
4. Engine coolant temperature is between 4-35°C (40-95°F)
5. Intake air temperature is between 4-35°C (40-95°F)
6. The ignition remains OFF for the duration of the test

The internal timer responsible for the sequencing of the EVAP system diagnostic routine is monitored by the PCM. If the PCM detects a fault in the internal timer, a DTC P2610 will set.

FTP Sensor Monitor

The performance of the FTP sensor is monitored continuously and regularly. The FTP sensor signal circuit is continuously monitored and DTC P0450, P0452, or P0453 will set if an out of range voltage is detected. DTC P0451 diagnostic monitors the FTP sensor signal voltage for a fixed or skewed value.

Noteworthy Ignition Information

Consider the following important information when servicing the ignition system

1. The ignition coils secondary output voltage is more than 40,000 volts. Avoid body contact with the ignition high voltage secondary components when the engine is running or personal injury may result.
2. The ignition timing is not adjustable. A timing indicator and timing marks are still visible at the crankshaft pulley but are not used to set or adjust the ignition timing. The PCM provides all ignition timing adjustments electronically.
3. Be careful not to damage the secondary ignition coil boots when servicing the ignition system. Rotate each ignition coil in order to loosen the boot from the spark plug before removing. Never pierce a secondary ignition boot for any testing purposes. Future ignition system problems are guaranteed if pinpoints or test lights are pushed through the secondary ignition component insulation during testing.
4. Do not use a conventional tachometer in order to check the engine speed on this ignition system. An inductive type pick-up will not provide reliable engine speed information. Use a scan tool in order to monitor the engine RPM.

Engine Idle Speed Control

The engine idle speed is controlled by the powertrain control module (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 engine 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.

Intake Air Temperature (IAT) 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. The IAT sensor measures the temperature of the air entering the intake manifold. The 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 the temperature is low, the resistance is high. The resistance decreases as the temperature increases. The IAT sensor is a 2-wire circuit with a reference or signal voltage and a ground coming from the PCM.

IAT Sensor Operation Chart

Scheme 184

The throttle position (TP) sensor is a potentiometer connected to the throttle shaft on the throttle body. By monitoring the voltage on the signal line, the powertrain control module (PCM) calculates the throttle position. As the throttle valve angle changes when the accelerator pedal is moved, the TP sensor signal also changes. At a closed throttle position, the output of the TP sensor is low. As the throttle valve opens, the output increases so that at wide open throttle, the output voltage should be more than 3.3 volts.

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

Scheme 185

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 (ACL) housing has 2 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 (7) by a vacuum solenoid (4). The solenoid is low side controlled by the powertrain control module (PCM). A constant supply of vacuum pressure is assured by the use of a vacuum check valve (8) and a vacuum storage chamber (6). The auxiliary intake air door is open when there is no vacuum applied. The PCM closes the door for most driving conditions. For diagnosis of the auxiliary intake air system refer to Auxiliary Intake Air System Diagnosis .