The engine control module (ECM) interacts with many more emission related components and systems, and monitors emission related components and systems for deterioration. OBD II diagnostics monitor the system performance and a diagnostic trouble code (DTC) sets if the system performance degrades.

The malfunction indicator lamp (MIL) operation and the DTC storage are dictated by the DTC type. A DTC is ranked as a Type A or Type B if the DTC is emissions related. Type C is a non-emissions related DTC.

The ECM is in the engine compartment. The ECM is the control center of the engine controls system. The ECM controls the following components:

The ECM constantly monitors the information from various sensors and other inputs, and controls the systems that affect the vehicle performance and the emissions. The ECM also performs diagnostic tests on various parts of the system. The ECM can recognize operational problems and alert the driver via the MIL. When the ECM detects a malfunction, the ECM stores a DTC. The condition area is identified bythe particular DTC that is set. This aids the technician in making repairs.

The ECM can supply 5 volts or 12 volts to the various sensors or switches. This is done through pull-up resistors to the regulated power supplies within the ECM. In some cases, even an ordinary shop voltmeterwill not give an accurate reading because the resistance is too low. Therefore, a DMM with at least 10 megaohms input impedance is required in order to ensure accurate voltage readings.

The ECM controls the output circuits by controlling the ground or the power feed circuit through the transistors or a device called an output driver module.

The electronically erasable programmable read only memory (EEPROM) is a permanent memory that is physically part of the ECM. The EEPROM contains program and calibration information that the ECM needs in order to control the powertrain operation.

Special equipment, as well as the correct program and calibration for the vehicle, are required in order to reprogram the ECM.

This vehicle is equipped with a theft deterrent system which interfaces with the ECM. If the ECM is replaced, program the new ECM with the frequency code of the theft deterrent module that is currently on the vehicle. The vehicle will not start until this procedure is completed.

The ECM employs an internal integrated circuit to continuously monitor the knock control evaluation circuit. The knock sensor (KS) module contains the circuitry that allows the ECM to utilize the knock sensor (KS) signals and diagnose the KS sensors and circuitry. If the ECM detects a fault in the ability of the KS module to sample these signals, a DTC sets.

The data link connector (DLC) is a 16-pin connector that provides the technician a means of accessing serial data for aid in the diagnosis. This connector allows the technician to use a scan tool in order to monitor the various serial data parameters, and display the DTC information. The DLC is located inside of the drivers compartment, underneath the dash.

The malfunction indicator lamp (MIL) is inside of the instrument panel cluster (IPC). The MIL is controlled by the ECM and illuminates when the ECM detects a condition that affects the vehicle emissions.

The ECM, by design, can withstand the normal current draws that are associated with the vehicle operations. However, care must be used in order to avoid overloading any of these circuits. When testing for opens or shorts, do not ground or apply voltage to any of the ECM circuits unless the diagnostic procedure instructs you to do so. These circuits should only be tested with a DMM.

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 this type of equipment.

Add-on electrical equipment, even when installed to these strict guidelines, may still cause the powertrain system to malfunction. This may also include equipment not connected to the vehicle electrical system, such as portable telephones and radios. Therefore, the first step in diagnosing any powertrain condition is to eliminate all of the aftermarket electrical equipment from the vehicle. After this is done, if the problem still exists, the problem may be diagnosed in the normal manner.

The electronic components that are used in the control systems are often designed to carry very low voltage. The electronic components are susceptible to damage caused by electrostatic discharge. Less than 100 volts of static electricity can cause damage to some electronic components. By comparison, it takes as much as 4,000 volts for a person to even feel the zap of a static discharge.

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. Static charges can cause damage, therefore, it is important to use care when handling and testing electronic components.

Perform a careful underhood inspection when performing any diagnostic procedure or diagnosing the cause of an emission test failure. This can often lead to repairing a condition without further steps. Use the following guidelines when performing an inspection:

A basic understanding of hand tools is necessary in order to effectively use this section of the Service Manual.

You must be familiar with some of the basics of engine operation and electrical diagnosis in order to use this section of the service manual.

The throttle actuator control (TAC) system is used to improve emissions, fuel economy, and driveability. The TAC system eliminates the mechanical link between the accelerator pedal and the throttle plate. The TAC system eliminates the need for a cruise control module and idle air control motor. The following is a list of TAC system components:

The ECM monitors the driver demand for acceleration with 2 APP sensors. The APP sensor 1 signal voltage range is from about 0.98–4.16 volts as the accelerator pedal is moved from the rest pedal position to the full pedal travel position. The APP sensor 2 range is from about 0.49–2.08 volts as the accelerator pedal is moved from the rest pedal position to the full pedal travel position. The ECM processes this information along with other sensor inputs to command the throttle plate to a certain position.

The throttle plate is controlled with a direct current motor called a throttle actuator control motor. The ECM can move this motor in the forward or reverse direction by controlling battery voltage and/or ground to 2 internal drivers. The throttle plate is held at a 7 percent rest position using a constant force return spring. This spring holds the throttle plate to the rest position when there is no current flowing to the actuator motor.

The ECM monitors the throttle plate angle with 2 TP sensors. The TP sensor 1 signal voltage range is from about 0.5–4.25 volts as the throttle plate is moved from 0 percent to wide open throttle (WOT). The TP sensor 2 voltage range is from about 4.45–0.7 volts as the throttle plate is moved from 0 percent to WOT.

The ECM performs diagnostics that monitor the voltage levels of both APP sensors, both TP sensors, and the throttle actuator control motor circuit. It also monitors the spring return rate of both return springs that are housed internal to the throttle body assembly. These diagnostics are performed at different times based on whether the engine is running, not running, or whether the ECM is currently in a throttle body relearn procedure.

Every ignition cycle, the ECM performs a quick throttle return spring test to make sure the throttle plate can return to the 7 percent rest position from the 0 percent position. This is to ensure that the throttle plate can be brought to the rest position in case of an actuator motor circuit failure. Observe, under cold conditions, the ECM commands the throttle plate to 7 percent with the ignition ON and the engine OFF to release any ice that may have formed on the throttle plate.

The engine control module (ECM) stores values that include the lowest possible throttle position (TP) sensor positions—0 percent, the rest positions—7 percent, and the return rate of both springs. These values will only be erased or overwritten if the ECM is reprogrammed or if a throttle body relearn procedure is performed. Observe, if the battery is disconnected, the ECM will immediately perform a throttle body relearn procedure when the ignition is turned ON.

A throttle body relearn procedure is performed anytime the ignition is turned ON, with the engine OFF for longer than 29 seconds when the following conditions have been met:

After 29 seconds, the ECM commands the throttle plate from the rest position to full closed, then to around 10 percent open. This procedure takes about 6–8 seconds. If any faults occur in the throttle actuator control (TAC) system, a DTC sets. At the start of this procedure, the scan tool TAC Learn Counter parameter should display 0, then count up to 11 after the procedure is completed. If the counter did not start at 0, or if the counter did not end at 11, a fault has occurred and a DTC should set.

There are 2 reduce power modes that the engine control module (ECM) can default to if an error is detected in the throttle actuator control (TAC) system. If an accelerator pedal position (APP) sensor 1 or APP sensor 2 circuit fault, throttle position (TP) sensor 2 circuit fault, or if a TP sensor 1 circuit fault is detected with some APP angle, the ECM goes into one of the 2 reduce power modes. In this mode, the engine torque is limited so that the vehicle cannot reach speeds of more than 100 km/h (60 mph). The ECM remains in this reduce power mode during the entire ignition cycle even if the fault is corrected.

If there is a condition with the throttle actuator control circuits, throttle actuator command vs actual position fault, return spring check fault, or a TP sensor 1 circuit fault, the ECM goes into the other reduce engine power mode. In this mode, the engine speed is limited to 2,500 RPM and the 3–6 fuel injectors are randomly turned OFF. At this time the Reduced Power indicator is commanded ON. The ECM remains in the reduce power mode during the entire ignition cycle even if the fault is corrected. Observe, if a TP sensor 1 or throttle actuator control circuit fault is present at the time the vehicle is at idle, with no accelerator pedal angle, the engine may stall.

The camshaft actuator system enables the engine control module (ECM) to change camshaft timing of all 4 camshafts while the engine is operating. The CMP actuator assembly (15) varies the 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 a camshaft. Modifying camshaft timing under changing engine demand provides better balance between the following performance concerns:

The CMP actuator assembly has an outer housing that is driven by an engine timing chain. Inside the assembly is a rotor with fixed vanes that is attached to the camshaft. Oil pressure that is applied to the fixed vanes will rotate a specific camshaft in relationship to the crankshaft. The movement of the intake camshafts will advance the intake valve timing up to a maximum of 50 crankshaft degrees. The movement of the exhaust camshafts will retard the exhaust valve timing up to a maximum of 50 crankshaft degrees. When oil pressure is applied to the return side of the vanes, the camshafts will return to 0 crankshaft degrees, or top dead center (TDC). The CMP actuator solenoid valve directs the oil flow that controls the camshaft movement. The ECM commands the CMP solenoid to move the solenoid plunger and spool valve until oil flows from the advance passage (11). Oil flowing thru the CMP actuator assembly from the CMP solenoid advance passage applies pressure to the advance side of the vanes in the CMP actuator assembly. When the camshaft position is retarded, the CMP actuator solenoid valve directs oil to flow into the CMP actuator assembly from the retard passage (3). The ECM can also command the CMP actuator solenoid valve to stop oil flow from both passages in order to hold the current camshaft position.

The ECM 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. The CMP actuator assembly also contains a lock pin (14) that prevents movement between the outer housing and the rotor vane assembly. The lock pin is released by oil pressure before any movement in the CMP actuator assembly takes place. The ECM is continuously comparing CMP sensor inputs with CKP sensor input in order to monitor camshaft position and detect any system malfunctions. If a condition exists in either the intake or exhaust camshaft actuator system, the opposite bank, intake or exhaust, camshaft actuator will default to 0 crankshaft degrees.

The fuel storage tank is made of high density polyethylene. The fuel storage tank is held in place by 2 metal straps that are attached to the under body of the vehicle. The tank shape includes a sump in order to maintain a constant supply of fuel around the fuel pump strainer during low fuel conditions or during aggressive maneuvers.

The fuel tank also contains a fuel vapor vent valve with a roll-over protection. The vent valve also features a 2-phase vent calibration which increases the fuel vapor flow to the canister when the operating temperatures increase the tank pressure beyond an established threshold.

In order to prevent refueling with leaded fuel, the fuel filler pipe has a built-in restrictor and a deflector. The opening in the restrictor will accept only the smaller unleaded gasoline fuel nozzle which must befully inserted in order to bypass the deflector. The tank is vented during filling by an internal vent tube inside of the filler pipe.

The fuel tank filler pipe is equipped with a turn to vent screw on the type cap which incorporates a ratchet action in order to prevent over-tightening.

The turn to vent feature allows the fuel tank pressure relief prior to removal. Instructions for proper use are imprinted on the cap cover. A vacuum safety relief valve is incorporated into this cap.

The modular fuel sender assembly mounts to the threaded opening of the plastic fuel tank with a seal and a retainer ring. The reservoir, containing the exterior inlet strainer, the electric fuel pump and the pump strainer, maintains contact with the tank bottom. This design provides:

The modular fuel sender assembly maintains an optimum fuel level in the reservoir (bucket). The fuel entering the reservoir is drawn in by the following components:

The electric fuel pump is a turbine pump which is located inside of the modular fuel sender. The electric fuel pump operation is controlled by the engine control module (ECM) through the fuel pump relay.

The strainers act as a coarse filter to perform the following functions:

Fuel stoppage at the strainer indicates that the fuel tank contains an abnormal amount of sediment or water. Therefore, the fuel tank will need to be removed and cleaned, and the filter strainer should be replaced.

The fuel filter is located on the fuel feed pipe, between the fuel pump and the fuel rail. The electric fuel pump supplies fuel through the in-line fuel filter to the fuel injection system. The fuel pressure regulator keeps the fuel available to the fuel injectors at a regulated pressure. Unused fuel is returned from the puel filter to the fuel tank by a separate fuel return pipe. The paper filter element (2) traps particles in the fuel that may damage the fuel injection system. The filter housing (1) is made to withstand maximum fuel system pressure, exposure to fuel additives, and changes in temperature. There is no service interval for fuel filter replacement. Replace a restricted fuel filter.

The EVAP line extends from the fuel tank vent valve to the EVAP canister and into the engine compartment. The EVAP line is made of nylon and connects to the EVAP canister with a quick connect fitting.

The fuel pressure regulator attaches to the fuel return pipe on the fuel sender assembly. The fuel pressure regulator is a diaphragm-operated relief valve. A software bias compensates the injector on-time because the fuel pressure regulator is not referenced to manifold vacuum. The injector pulse width varies with the signal from the mass air flow (MAF)/intake air temperature (IAT) sensor.

With the engine running at idle, the system fuel pressure at the pressure test connection should be between 380–410 kPa (55–60 psi). With the system pressurized and the pump OFF the pressure should stabilize and hold. If the pressure regulator supplies a fuel pressure which is too low or too high, a driveability condition will result.

The fuel rail consists of 3 parts:

The fuel rail is mounted on the intake manifold and distributes the fuel to each cylinder through the individual injectors.

The fuel injector is a solenoid device that is controlled by the ECM. When the ECM energizes the injector coil, a normally closed ball valve opens, allowing the fuel to flow past a director plate to the injector outlet. The director plate has holes that control the fuel flow, generating a dual conical spray pattern of finely atomized fuel at the injector outlet. The fuel from the outlet is directed at both of the intake valves, causing the fuel to become further vaporized before entering the combustion chamber.

The fuel injectors will cause various driveability conditions if the following conditions occur:

The fuel pump relay allows the ECM to energize the fuel pump. The ECM enables the fuel pump whenever the crankshaft position (CKP) sensor pulses are detected.

The engine is fueled by six individual injectors, one for each cylinder, that are controlled by the ECM. The ECM controls each injector by energizing the injector coil for a brief period once every other engine revolution. The length of this brief period, or pulse, is carefully calculated by the ECM to deliver the correct amount of fuel for proper driveability and emissions control. The period of time when the injector is energized is called the pulse width and is measuredin milliseconds, thousandths of a second. While the engine is running, the ECM is constantly monitoring the inputs and recalculating the appropriate pulse width for each injector. The pulse width calculation is based on the injector flow rate, mass of fuel the energized injector will pass per unit of time, the desired air/fuel ratio, and actual air mass in each cylinder and is adjusted for battery voltage, short term, and long term fuel trim. The calculated pulse is timed to occur as each cylinders intake valves are closing to attain largest duration and most vaporization.

Fueling during a crank is slightly different than fueling during an engine run. As the engine begins to turn, a prime pulse may be injected to speed starting. As soon as the ECM can determine where in the firing order the engine is, the ECM begins pulsing the injectors. The pulse width during the crank is based on the coolant temperature and the engine load. The fueling system has several automatic adjustments in order to compensate for the differences in the fuel system hardware, the driving conditions, the fuel used, and the vehicle aging. The basis for the fuel control is the pulse width calculation that is described above. Included in this calculation are an adjustment for the battery voltage, the short term fuel trim, and the long term fuel trim. The battery voltage adjustment is necessary since the changes in the voltage across the injector affect the injector flow rate. The short term and the long term fuel trims are fine and gross adjustments to the pulse width that are designed in order to maximize the driveability and emissions control. These fuel trims are based on the feedback from the oxygen sensors in the exhaust stream and are only used when the fuel control system is in a Closed Loop operation.

Under certain conditions, the fueling system will turn OFF the injectors for a period of time. This is referred to as fuel shut-off. Fuel shut-off is used in order to improve traction, save fuel, improve emissions, and protect the vehicle under certain extreme or abusive conditions.

In case of a major internal problem, the ECM may be able to use a back-up fuel strategy for limp in mode that will run the engine until service can be performed.

The ECM controls the fuel injectors based on information that the ECM receives from several information sensors. Each injector is fired individually in the engine firing order, which is called sequential fuel injection. This allows precise fuel metering to each cylinder and improves the driveability under all of the driving conditions.

The ECM has several operating modes for fuel control, depending on the information that has been received from the sensors.

When the ECM detects reference pulses from the CKP sensor, the ECM will enable the fuel pump. The fuel pump runs and builds up pressure in the fuel system. The ECM then monitors the MAF, IAT, engine coolant temperature (ECT), and the throttle position (TP) sensor signal in order to determine the required injector pulse width for starting.

If the engine is flooded with fuel during starting and will not start, the Clear Flood Mode can be manually selected. To select Clear Flood Mode, push the accelerator to wide open throttle (WOT). With this signal, the ECM will completely turn OFF the injectors and will maintain this stage as long as the ECM indicates a WOT condition with engine speed below 1,000 RPM.

The Run Mode has 2 conditions: Open Loop operation and Closed Loop operation. When the engine is first started and the engine speed is above 480 RPM, the system goes into Open Loop operation. In Open Loop operation, the ECM ignores the signals from the oxygen sensors and calculates the required injector pulse width based primarily on inputs from the MAF, IAT and ECT sensors.

In Closed Loop, the ECM adjusts the calculated injector pulse width for each bank of injectors based on the signals from each oxygen sensor.

The ECM monitors the changes in the TP and the MAF sensor signals in order to determine when the vehicle is being accelerated. The ECM will then increase the injector pulse width in order to provide more fuel for improved performance.

The ECM monitors changes in TP and MAF sensor signals to determine when the vehicle is being decelerated. The ECM will then decrease injector pulse width or even shut OFF injectors for short periods to reduce exhaust emissions, and for better (engine braking) deceleration.

The ECM can compensate in order to maintain acceptable vehicle driveability when the ECM sees a low battery voltage condition. The ECM compensates by performing the following functions:

The ECM has the ability to completely turn OFF all of the injectors or selectively turn OFF some of the injectors when certain conditions are met. These fuel shut-off modes allow the ECM to protect the engine from damage and also to improve the vehicles driveability.

The ECM will disable all of the six injectors under the following conditions:

The ECM will selectively disable the injectors under the following conditions:

The evaporative emission (EVAP) control system limits fuel vapors from escaping into the atmosphere. Fuel tank vapors are allowed to move from the fuel tank, due to pressure in the tank, through the vapor pipe, into the EVAP canister. Carbon in the canister absorbs and stores the fuel vapors. Excess pressure is vented through the vent line to atmosphere. The EVAP canister stores the fuel vapors until the engine is able to use them. At an appropriate time, the control module will command the EVAP purge valve ON, open, allowing engine vacuum to be applied to the EVAP canister. Fresh air is drawn through the canister, pulling fuel vapors from the carbon. The air/fuel vapor mixture continues through the EVAP purge pipe and EVAP purge valve into the intake manifold to be consumed during normal combustion.

The EVAP system consists of the following components:

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

The EVAP purge valve controls the flow of vapors from the EVAP system to the intake manifold. This normally closed valve is pulse width modulated (PWM) by the control module to precisely control the flow of fuel vapor to the engine. The valve will also be opened during some portions of the EVAP testing, allowing engine vacuum to enter the EVAP system.

The electronic ignition (EI) system produces and controls a high-energy secondary spark. This spark is used to ignite the compressed air/fuel mixture at precisely the correct time. This provides optimal performance, fuel economy, and control of exhaust emissions. This ignition system uses an individual coil for each cylinder. The ignition coils are mounted in the center of each camshaft cover with short integrated boots connecting the coils to the spark plugs. The driver modules within each ignition coil are commanded ON/OFF by the engine control module (ECM). The ECM primarily uses engine speed, the MAF sensor signal, and position information from the crankshaft position (CKP) and the camshaft position (CMP) sensors. This controls the sequence, dwell, and timing of the spark. The EI system consists of the following components:

The crankshaft position (CKP) sensor works in conjunction with a 58 tooth reluctor wheel on the crankshaft. The engine control module (ECM) monitors the voltage between the CKP sensor signal circuits. As each reluctor wheel tooth rotates past the sensor, the sensor creates an analog signal. This analog signal is processed by the ECM. The reluctor wheel teeth are 6 degrees apart. Having only 58 teeth leaves a 12 degree span that is uncut. This creates a signature pattern that enables the ECM to determine the CKP. The ECM can determine which pair of cylinders is approaching top dead center based on the CKP signal alone. The camshaft position (CMP) sensor signals are used in order to determine which of these 2 cylinders is on a firing stroke, and which is on the exhaust stroke. The ECM uses this to properly synchronize the ignition system, the fuel injectors, and the knock control. This sensor is also used in order to detect misfire.

This engine uses 4 camshaft position (CMP) sensors, one for each camshaft. The CMP sensor signals are a digital ON/OFF pulse, output 4 times per revolution of the camshaft. The CMP sensor does not directly affect the operation of the ignition system. The CMP sensor information is used by the engine control module (ECM) to determine the position of the 4 camshafts relative to the crankshaft position. By monitoring the CMP and crankshaft position (CKP) signals the ECM can accurately time the operation of the fuel injectors. The ECM supplies the CMP sensor with a 5-volt reference circuit and a low reference circuit. The CMP sensor signals are an input to the ECM. These signals are also used to detect camshaft alignment with the crankshaft.

Each ignition coil contains a solid state driver module as its primary element. The engine control module (ECM) signals the coil driver to initiate a firing event by applying ignition control (IC) circuit voltage for the appropriate time, or dwell. When the voltage is removed the coil fires the spark plug. The ignition coils use the following circuits:

The engine control module (ECM) controls all ignition system functions, and constantly corrects the spark timing. The ECM monitors information from various sensor inputs that include the following components:

You can diagnose all of the sensors and most of the input circuits with a scan tool. Within this section is a short description of how to use a scan tool wherever possible to diagnose these circuits. You can also use the scan tool to compare the values for an engine that is running normally with the engine you are diagnosing.

The knock sensor (KS) system detects engine knocking or pinging. The ECM will retard the spark timing based on the signals from the KS system. The KS produce an AC voltage that is sent to the engine control module (ECM). The amount of the AC voltage produced is proportional to the amount of knock.

The ECM monitors the voltage of the sensors after each cylinder has fired.

If knock occurs in any of the cylinders, the ignition will be retarded for that particular cylinder. If the knocking then stops, the ignition will be restored to what it was before in steps.

Should knocking continue in the same cylinder in spite of the ignition being retarded, the ECM will retard the ignition an additional steps, and so on, up to a maximum of 12 degrees of retard. The ignition will also be retarded at high ambient temperatures in order to counteract knocking tendencies provoked by high intake air temperatures.

Should either bank 1 or bank 2 sensor fail to work, or should an internal circuit problem occur, the ignition timing will then use a default strategy. The default strategy will retard the ignition the maximum allowed amount to protect the engine from possible damage.

The MAF sensor measures the amount of air coming into the engine. This direct airflow measurement is more accurate than the calculated airflow information obtained from the other sensor inputs. The MAF sensor also houses an integrated intake air temperature (IAT) sensor. The MAF sensor uses the following circuits:

The MAF sensor that is used on this vehicle is a hot film type and is used in order to measure the air flow rate. The MAF output voltage is a function of the power required to keep the air flow sensing elements at a fixed temperature above the ambient temperature. The air flowing through the sensor cools the sensing elements. The amount of cooling is proportional to the amount of air flow. As the air flow increases, more current is needed in order to maintain the hot film at a constant temperature. The MAF sensor converts the changes in the current draw to a voltage signal that the ECM monitors. The ECM calculates the air flow based on this signal.

The ECM monitors the MAF sensor signal voltage and can determine if the sensor signal voltage is too low or too high. The ECM can also detect airflow that is inappropriate for a given operating condition based on the signal voltage.

The scan tool displays the MAF value and displays the value in grams per second (g/s). Values should change rather quickly on acceleration, but should remain fairly stable at any given engine speed. If the ECM detects a condition with the MAF sensor circuits, the following DTCs set:

The characteristic torque curve of a normally aspirated engine depends mainly on how the engines average pressure changes over the engine speed band. The average pressure is proportional to the volume of the air mass present in the cylinder when the inlet valve is closed. The design of the inlet system determines how large an air mass can be drawn into a cylinder at a given engine speed.

An intake manifold runner control (IMRC) valve (2) is used to change the intake manifold runner configuration. When the IMRC valve is open, the intake manifold is configured to one large plenum (4). When the IMRC valve is closed, the intake manifold is configured to two smaller plenums (3). The two intake manifold runner sizes result in different torque curves which improves performance at low and high engine speeds. The IMRC valve is located in the intake manifold (1). The IMRC valve solenoid is supplied with ignition 1 voltage and is controlled by the engine control module (ECM).