Engine Controls (Introduction) -- 3.5L (L66): Overview Saturn VUE I

Engine Controls Schematic Icons

Engine Controls Schematic Icons Icon Icon Definition NOTE: The OBD II symbol is used on the circuit diagrams in order to alert the technician that the circuit is essential for proper OBD II emission control circuit operation. Any circuit which fails and causes the malfunction indicator lamp (MIL) to turn ON, or causes emissions-related component damage, is identified as an OBD II circuit

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Malfunction Indicator Lamp (MIL) Operation

The malfunction indicator lamp (MIL) is located in the instrument panel cluster. The MIL will display as either SERVICE ENGINE SOON or one of the following symbols when commanded ON

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The MIL indicates that an emissions related fault has occurred and vehicle service is required.

The following is a list of the modes of operation for the MIL

1. The MIL illuminates when the ignition is turned ON, with the engine OFF. This is a bulb test to ensure the MIL is able to illuminate.
2. The MIL turns OFF after the engine is started if a diagnostic fault is not present.
3. The MIL remains illuminated after the engine is started if the control module detects a fault. A diagnostic trouble code (DTC) is stored any time the control module illuminates the MIL due to an emissions related fault. The MIL turns OFF after three consecutive ignition cycles in which a Test Passed has been reported for the diagnostic test that originally caused the MIL to illuminate.
4. The MIL flashes if the control module detects a misfire condition which could damage the catalytic converter.
5. When the MIL is illuminated and the engine stalls, the MIL will remain illuminated as long as the ignition is ON.
6. When the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition is cycled OFF and then ON.

Fail-Safe Function

When a malfunction occurs within the engine control system, the PCM maintains control over the fuel injection system, the idle speed control system, etc. The 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 as follows

1. The IAT sensor
2. The TAC system
3. The HO2S heater circuits
4. The KS system
5. The CPU in the PCM
6. The fuel cut-off for certain system failures

Catalyst Monitor Diagnostic Operation

The powertrain control module (PCM) uses certain diagnostic strategies known as primary system based diagnostics that evaluate the various primary system operations. The primary system based diagnostics also evaluate the various primary system operations affect on vehicle emissions. Some of the primary system based diagnostics are listed here with a brief functional description of the diagnostics involved.

The OBD 2 catalyst monitor diagnostic measures the oxygen storage capacity of the 3-way catalytic converter (TWC). 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. When the TWC catalyst becomes less effective in promoting chemical reactions, the catalyst's capacity to store and release oxygen is generally degraded. The OBD 2 catalyst monitor diagnostic is based on a correlation between the conversion efficiency of the TWC catalyst and the oxygen storage capacity of the catalyst. A good catalyst, e.g., 95 percent hydrocarbon conversion efficiency, will show a relatively flat output voltage on the post-catalyst sensor, HO2S 2. A degraded catalyst, 65 percent hydrocarbon conversion, will show greatly increased activity in the output voltage from the post catalyst HO2S.

The post-catalyst HO2S is used to measure the oxygen storage and release capacity of the catalyst in the TWC. A high oxygen storage capacity indicates a good catalyst. A low oxygen storage capacity indicates a failing catalyst. The TWC and the HO2S 2 must be at operating temperature in order to achieve the correct oxygen sensor voltages, like those shown in the post-catalyst HO2S Outputs graphic.

The catalyst monitor diagnostic is sensitive to the following conditions

1. Exhaust leaks
2. HO2S contamination
3. Alternative fuels

Exhaust system leaks may cause any of the following results

1. A false failure for a normally functioning, good catalyst.
2. Prevent a degraded catalyst from failing the catalyst monitor diagnostic.
3. Prevent the catalyst monitor diagnostic from running.

The presence of HO2S contaminants may prevent the catalyst monitor diagnostic from functioning properly.

Three-Way Catalyst Oxygen Storage Capacity

The TWC catalyst must be monitored for efficiency. In order to accomplish this, the control module monitors the pre-catalyst (HO2S 1) and post-catalyst (HO2S 2) oxygen sensors. When the TWC is operating properly, the post-catalyst oxygen sensor will have significantly less activity than the pre-catalyst oxygen sensor. The TWC stores and releases oxygen as needed during the normal reduction and oxidation process. The control module will calculate the oxygen storage capacity using the difference between the pre-catalyst and post-catalyst oxygen sensor voltage levels. If the activity of the post-catalyst oxygen sensor approaches that of the pre-catalyst oxygen sensor, the catalyst's efficiency is degraded.

Stepped or staged testing levels allow the PCM to statistically filter test information. This prevents falsely passing or falsely failing the catalyst monitor oxygen storage capacity test. The calculations performed by the on-board diagnostic system are very complex. Post-catalyst oxygen sensor activity should not be used to determine the oxygen storage capacity unless directed by the service manual.

A 2-stage test is used to monitor the catalyst efficiency. Failure of the first stage of the test will indicate that the catalyst requires further testing in order to determine the catalyst efficiency. The second stage test looks at the inputs from the pre-catalyst and post-catalyst HO2S sensors more closely in order to determine if the catalyst is actually degraded. This two stage test further increases the accuracy of the oxygen storage capacity monitor. Failing the first stage test DOES NOT indicate a failed catalyst. The catalyst may be marginal or the fuels sulfur content could be very high.

Aftermarket HO2S characteristics may be significantly different from the original equipment manufacturer HO2S. An inferior HO2S may lead to a false pass or a false fail of the catalyst monitor diagnostic. An aftermarket catalytic converter that does not contain the same amount of cerium as the original catalytic converter can cause a false DTC to set. An incorrect amount of cerium in the catalyst can alter the correlation between the oxygen storage and the conversion efficiency of the TWC.

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A good TWC catalyst will show a very active output voltage on the pre-catalyst heated oxygen sensor (1). A good catalyst, 95 percent hydrocarbon conversion, will show a relatively flat output voltage on the post-catalyst heated oxygen sensor (2).

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A degraded TWC catalyst, 65 percent hydrocarbon conversion, will show greatly increased activity in the output voltage from the post-catalyst heated oxygen sensor (2). 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 (1).

Misfire Monitor Diagnostic Operation

The misfire monitor diagnostic is based on crankshaft rotational velocity, reference period, variations. The powertrain control module determines the crankshaft rotational velocity using the crankshaft position sensor and the camshaft position sensor. When a cylinder misfires the crankshaft actually slows down momentarily. By monitoring the crankshaft and the camshaft position sensor signals, the control module can calculate when a misfire occurs.

For a non-catalyst damaging misfire, the diagnostic will be required to report a misfire that is present within 1000-3200 engine revolutions.

For a catalyst damaging misfire, the diagnostic will respond to a misfire that is within 200 engine revolutions.

Rough roads may cause a false misfire detection. A rough road will cause torque to be applied to the drive wheels and the drive train. This torque can intermittently decrease the crankshaft rotational velocity and cause a false misfire detection.

On automatic transaxle equipped vehicles, the torque converter clutch (TCC) will be disabled whenever a misfire is detected. Disabling the TCC isolates the engine from the rest of the drive line and minimizes the effect of the drive wheel inputs (torque) on the crankshaft rotation.

When the TCC has been disabled as a result of a misfire detection, the TCC will be re-enabled after approximately 3200 engine revolutions with no misfire is detected. The TCC will remain disabled whenever a misfire is detected. This allows the misfire diagnostic to evaluate the system.

Fuel Trim System Monitor Diagnostic Operation

The fuel system monitor diagnostic averages of short-term and long-term fuel trim values. If these fuel trim values stay at the fuel trim limits for a calibrated period of time, a malfunction is indicated. The fuel trim diagnostic compares the averages of the short-term fuel trim values and the long-term fuel trim values to the rich and lean thresholds. If either value is within the thresholds, a pass is recorded. If both values are outside the acceptable thresholds, a rich or lean DTC will be recorded.

In order to meet OBD ll requirements, the control module uses weighted fuel trim cells in order to determine the need to set a fuel trim DTC. A fuel trim DTC can only be set if the fuel trim counts in the weighted fuel trim cells exceed the specifications. A vehicle that has a fuel trim problem that is causing a concern under certain conditions but operates fine under other conditions may not set a fuel trim DTC. For example an engine that is idling high due to a small vacuum leak or an engine that is running rough due to a large vacuum leak may set an idle speed DTC or an HO2S DTC but not a fuel trim DTC.

A fuel trim DTC may be triggered by many different vehicle faults. Use all of the diagnostic information available when diagnosing a fuel trim fault.

Rocker Arm Oil Control System Description

The 3.5L RPO-L66 engine has a high speed cam system that increases engine output above 4,400 RPM. The increase in power is possible because valve lift is significantly increased between 4,400 and 6,500 RPM. A second camshaft lobe with a high lift profile is ground 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.

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The three intake rocker arms (2 and 3) ride on rocker arm shafts as do the two exhaust rocker arms (4). The rocker arm shafts supply engine oil to the rocker arms. When the flow of oil to the rocker arms increases, the synchronizing pistons (1) move and lock the three rocker arms together. With all three rocker arms locked together, the high speed cam lobe opens and closes the intake valves (7).

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The flow of oil thru the rocker shafts to the rocker arms is controlled by the rocker arm oil control solenoid. A rocker arm oil pressure switch monitors the operation of the oil control solenoid. The rocker arm oil control solenoid (1) and the oil pressure switch (3) are located near the engine oil filter (2) on the lower right rear corner of the engine.

System Operation

The rocker arm oil control system is an electronically controlled, hydraulically operated system that provides good low speed torque and high speed horsepower. The engine control module uses an electronic solenoid to control the flow of oil to the rocker arms. In order to determine when to transition from low to high speed operation, the control module relies on the following information

1. Engine speed
2. Engine load
3. Engine operating temperature
4. Vehicle speed

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At engine speeds below 4,400 RPM, the low-medium speed cam lobes (5) open and close the intake valves (7) thru the low-medium speed rocker arms (1). During low-medium speed operation, the rocker arm oil control solenoid is OFF and there is no oil flow to the rocker arms. Without oil flow there is no oil pressure, and the piston spring (3) keeps the synchronizing pistons (4) at rest in their bores within the three rocker arms (1 and 2). This allows the high speed rocker arm (2) to move independently of the two low-medium speed rocker arms (1) while following the high speed cam lobe.

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When engine speed exceeds 4,400 RPM engine oil is allowed to flow unobstructed to the rocker arms. This flow of oil into the rocker arm oil passages creates an increase in oil pressure. The increase in oil pressure moves the synchronizing pistons (3) further into their bores, compressing the piston spring. As the spring is compressed, the shifted pistons lock all three rocker arms together (1 and 2). When locked together, the low-medium speed rocker arms (1) follow the movement of the high speed rocker arm (2). Because the high speed rocker arm (2) is following the high speed cam lobe (4), the intake valves (6) open with more lift.

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The flow of engine oil thru the rocker shafts to the intake rocker arms (4 and 6) is controlled by the rocker arm oil control solenoid (1). The oil control solenoid (1) has a plunger that moves a spool valve (2) located in the path of the rocker arm oil supply (7). When the oil control solenoid is energized, the spool valve is positioned to allow maximum oil flow to the intake rocker arms. Because of the restriction to full oil flow in the rocker arm oil passages, oil pressure increases. Excess oil is returned to the oil pan thru the oil return passages (5). The rocker arm oil pressure switch (11) detects oil pressure when the rocker arm oil control solenoid (1) is ON. The oil pressure switch input enables the engine control module to monitor the operation of the rocker arm oil control solenoid.

Rocker Arm Actuator System Operation

If there is an open or short in the rocker arm oil control solenoid or the solenoid electrical circuit, DTC P2648 or DTC P2649 sets. If the rocker arm oil pressure switch detects oil pressure when there should be no pressure, DTC P2647 sets. If the rocker arm oil pressure switch detects no oil pressure when there should be pressure, DTC P2646 sets.

Fuel System Overview

The fuel system is a returnless on-demand design. The fuel pressure regulator is a part of the primary fuel tank module, eliminating the need for a return pipe from the engine. A returnless fuel system reduces the internal temperature of the fuel tank by not returning hot fuel from the engine to the fuel tank. Reducing the internal temperature of the fuel tank results in lower evaporative emissions.

An electric turbine style fuel pump attaches to the primary fuel tank module inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter, past the fuel pressure regulator, and through the fuel feed pipe to the fuel injection system. The fuel pressure regulator has a T-joint that diverts the needed fuel to the fuel rail with the unused fuel dropping back into the reservoir of the primary fuel tank module. The primary fuel tank module contains a reverse flow check valve. The check valve and the fuel pressure regulator maintain fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times.

The primary fuel tank module also contains a primary jet pump and a secondary jet pump. Fuel pump flow loss, caused by vapor expulsion in the pump inlet chamber, is diverted to the primary jet pump and the secondary jet pump through a restrictive orifice located on the pump cover. The primary jet pump fills the reservoir of the primary fuel tank module. The secondary jet pump creates a venturi action which causes the fuel to be drawn from the secondary side of the fuel tank, through the fuel transfer pipe, to the primary side of the fuel tank.

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The fuel tank stores the fuel supply. The fuel tank is located in the rear of the vehicle. The fuel tank is held in place by 2 metal straps that attach to the under body of the vehicle. The fuel tank is molded from high-density polyethylene.

In order to provide space for a driveshaft though the center area of the tank, the fuel tank is a saddle configuration. Because of the saddle shape of the tank two fuel tank modules are required. The primary fuel tank module is located on the right side of the tank. The secondary fuel tank module is located on the left side of the tank.

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The fuel fill pipe has a built-in restrictor in order to prevent refueling with leaded fuel.

Air/Fuel Ratio Feedback Compensation - Closed Loop Operation

The wide band heated oxygen sensor (HO2S) measures the amount of oxygen in the exhaust system and provides more information than the switching style HO2S. The wide band sensor consists of an oxygen sensing cell, an oxygen pumping cell, and a heater. The exhaust gas sample passes through a diffusion gap between the sensing cell and the pumping cell. The engine control module (ECM) supplies a voltage to the HO2S and uses this voltage as a reference to the amount of oxygen in the exhaust system. An electronic circuit within the ECM controls the pump current through the oxygen pumping cell in order to maintain a constant voltage in the oxygen sensing cell. The ECM monitors the voltage variation in the sensing cell and attempts to keep the voltage constant by increasing or decreasing the amount of current flow to the pumping cell. By measuring the amount of current required to maintain the voltage in the sensing cell, the ECM can determine the concentration of oxygen in the exhaust. The HO2S voltage is displayed as a lambda value. A lambda value of 1 is equal to a stoichiometric air fuel ratio of 14.7:1. Under normal operating conditions, the lambda value will remain around 1. When the system is lean, the oxygen level will be high and the lambda signal will be high or more than 1. When the oxygen level is low, the lambda signal will be low or less than 1. The ECM uses this information to maintain the proper air/fuel ratio.

In order to obtain efficient performance of the 3-way catalytic converter (TWC) and a high clarification rate of CO, HC and NOx in the exhaust gas stream, the air/fuel mixture must be kept as close to the theoretical air/fuel ratio of 14.7:1 as possible. In order to accomplish this the PCM first compares the actual lambda value of the heated oxygen sensor 1 (HO2S 1) with the reference value of 1. If the HO2S 1 lambda value is less than the 1, the PCM determines that the air/fuel ratio is richer than the theoretical air/fuel ratio and reduces the fuel. If the lambda value of the HO2S 1 is more than 1, the PCM determines that the air/fuel ratio is lean and increases the fuel. By repeating these operations, the PCM can adjust the air/fuel ratio in order to be closer to the theoretical air/fuel ratio. Control of the fuel delivery system as just described is known as CLOSED LOOP operation.

Closed Loop Fuel Control Operation

The Closed Loop fuel control operation will not take place under any of the following conditions

1. At engine start up
2. When the fuel injection is increased just after engine start up.
3. When the engine coolant temperature (ECT) sensor is indicating a low coolant temperature.
4. When the engine is operating under a high demand, such as at wide open throttle (WOT).
5. During fuel cutoff
6. When the HO2S 1 is cold-Open Loop operation.

Control of the air supply that is mixed with the metered fuel is detailed in the description of the air intake system. Refer to Air Intake System Description .

EVAP System Operation

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 and EVAP vent valve 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. With the EVAP vent valve OFF, open, fresh air will be drawn through the valve and vent line 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 control module uses several tests to determine if the EVAP system is leaking.

Electronic Ignition (EI) System Description

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. The powertrain control module (PCM)
2. The 6 ignition coil assemblies
3. The crankshaft position (CKP) sensor
4. The camshaft position (CMP) sensor
5. The 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.

Operation

The powertrain control module (PCM) uses reference pulses from the crankshaft position (CKP) sensor in order to determine the engine speed. The PCM cannot operate the ignition system or the fuel injectors without the engine speed signal from the CKP sensor. The PCM controls the ignition timing by controlling the ignition coils.

Each ignition coil has a built-in ignition module that controls the current flow in the primary coil winding. When the current flow is interrupted, the electrical field around the primary coil collapses and a high voltage is induced in the secondary coil. The secondary coil voltage travels from the coil output terminal, through the spark plug boot, and across the spark plug gap to the engine block. As a fail-safe function the ignition control module sends an ignition confirmation signal back to the PCM whenever the primary field collapses.

The camshaft position (CMP) sensor input is used to detect an engine misfire. The PCM also uses the CMP sensor signal as an input for modifying the fuel injection timing and for modifying the ignition timing.

The PCM receives information on the engine status from various engine sensors and then selects the most appropriate ignition timing settings from within the PCM's programming. The following are the most important inputs for determining ignition timing requirements

1. The engine speed
2. The accelerator pedal position (APP)
3. The intake air volume
4. The engine coolant temperature (ECT)
5. The knock sensor (KS) input

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The crankshaft position (CKP) sensor (1) is located in the front cover of the cylinder block near the crankshaft pulley. The CKP sensor is actually two separate sensors, located 22.5 degrees apart, within the same housing. Both CKP sensor A and CKP sensor B function the same and provide an AC signal that increases in both frequency and amplitude as the engine speed increases. The CKP sensor signal is sent to the PCM in order to indicate the RPM and the crankshaft position. The PCM uses the information from both CKP sensors in order to perform the following functions

1. Determine engine speed
2. Determine accurate crankshaft position
3. Calculate ignition system and fuel injection timing
4. Provide continued engine operation even when one sensor fails
5. Report engine misfire-when used with CMP sensor input

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The CKP sensor signal rotor (1) is an integral part of the crankshaft pulley (3) and is located behind the timing belt cover. When the crankshaft rotates, the CKP sensor signal rotor teeth pass by the CKP sensor (2) 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 tooth on the crankshaft signal rotor. The rotor has 24 evenly spaced teeth, with two teeth missing, indicating top dead center (TDC) and producing 22 electrical pulse per revolution. CKP sensor A and CKP sensor B each provide position signals to the PCM. The PCM relies on the signal from CKP sensor A first, and uses the signal from sensor B only when sensor A is missing or unintelligible.

Results of Faulty Knock Sensor Operation

A KS that falsely indicates detonation can cause the PCM to retard the ignition timing unnecessarily. Reduced spark advance can cause any of the following conditions

1. Poor fuel economy
2. Sluggish engine performance
3. 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 any of the following concerns

1. An excessive engine detonation
2. Engine damage during heavy engine loads
3. Higher exhaust emissions

Exhaust Gas Recirculation (EGR) System Description

The exhaust gas recirculation (EGR) system controls the formation of oxides of nitrogen (NOx) emissions by recirculating the exhaust gases into the combustion chamber. NOx emissions increase with combustion chamber temperatures. Controlling the high combustion chamber temperatures will help limit the formation of NOx emissions. The EGR system accomplishes this by admitting controlled amounts of exhaust gas into the intake manifold to mix with the incoming air. Mixing exhaust gases with incoming air/fuel mixture modifies the combustion process resulting in lower combustion chamber temperatures.

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The EGR valve (1) is located on the left corner of the front engine bank. The valve uses a stepper motor to drive a worm gear. The worm gear is in mesh with a plunger that controls the exhaust gas passage opening. Plunger movement is monitored by a position sensor. The powertrain control module (PCM) uses a pulse width modulated (PWM) signal to operate the stepper motor. By rotating the stepper motor in different directions, the PCM controls the opening of the exhaust gas passage to the intake manifold.

The PCM uses the inputs from various sensors in order to control the operation of the EGR valve. Information from the engine coolant temperature (ECT) sensor, the throttle position (TP) sensor, the vehicle speed sensor (VSS), and the manifold absolute pressure (MAP) sensor are critical for proper EGR valve operation. Under heavy engine loads, when the demand for power is high, the EGR valve is closed. In order to insure a smooth idle and stable engine operation, the EGR valve is also closed at closed throttle engine operation. The EGR valve is usually open during low and medium engine loads and speeds. Combining pre-programmed engine calibrations with various sensor inputs, the PCM calculates the optimum opening of the EGR valve.

The EGR valve position sensor enables the PCM to know if the valve plunger is actually in the desired position. Information from the sensor is used to increase or decrease the plunger opening, in order to achieve the correct flow. If the position sensor signal indicates that the plunger position is incorrect and cannot be adjusted, a diagnostic trouble code (DTC) will set.

Results Of Incorrect Operation of the EGR System

Excessive EGR valve flow may cause any of the following conditions

1. The engine stalling
2. Rough idle, surging, or engine hesitation
3. Lower fuel economy
4. Incomplete combustion and high exhaust emissions

Inadequate EGR valve flow may cause any of the following conditions

1. Engine detonation
2. Excessive exhaust emissions

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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 (4) and passes through the air cleaner element (3). Next the air enters the air cleaner upper assembly (2) and flows through the inlet air duct (1), 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 inlet air duct contains the intake air temperature (IAT) sensor 1.

The following components are directly or indirectly a part of the air supply system.

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The throttle body contains a throttle valve that controls the amount of air entering the engine. The throttle valve is opened and closed by the throttle actuator control (TAC) motor. The TAC motor is an integral part of the TAC module assembly (2) mounted on the side of the throttle body. The TAC motor is controlled by commands from the powertrain control module (PCM), passed to the module circuitry through a dedicated serial data line. The TAC module also contains two throttle position (TP) sensors, TP sensor 1 and TP sensor 2. For detailed information on the operation of the TAC system refer to Throttle Actuator Control (TAC) System Description .

In order to prevent cold weather icing and stabilize cold weather performance, the throttle body is warmed by engine coolant (4). The manifold absolute pressure (MAP) sensor (6) is located on top of throttle body.