Engine Control System & Fuel System - 6.6l (lmm) - Description and Operation GMC Sierra II

Scheme 65

The accelerator pedal position (APP) sensor is mounted inside the accelerator pedal control assembly. The sensor is made up of the two individual sensors within a single housing. Each sensor has a unique functionality to determine pedal position.

The accelerator pedal position (APP) system along with the engine control module (ECM) is used to calculate and control the amount of acceleration and deceleration through fuel injector control.

Scheme 66

The exhaust particulate filter (EPF) captures diesel exhaust gas particulates, preventing their release into the atmosphere. This is accomplished by forcing particulate-laden exhaust (1) through a filter substrate of porous cells, which removes the particulates from the exhaust gas. The exhaust gas enters the filter, but because every other cell of the filter is capped at the opposite end, the exhaust particulates cannot exit the cell. Instead, the exhaust gas passes through the porous walls of the cell leaving the particulates trapped on the cell wall. The cleaned exhaust gas exits the filter through the adjacent cell. The EPF is capable of reducing more than 90 percent of particulate matter (PM).

Scheme 67

Diesel Oxidation Catalyst

The diesel oxidation catalyst (DOC) (7) has two functions. One function is to reduce emissions of non methane hydro-carbons (NMHC) and carbon monoxide (CO), from the exhaust gases. The other function is to help start a regeneration event by converting the fuel-rich exhaust gases to heat. The engine control module (ECM) monitors the functionally of the DOC by determining if the exhaust gas temperature (EGT) sensor 1 (1) reaches a predetermined temperature during a regeneration event. The DOC and the exhaust particulate filter (EPF) (6) are downstream of the turbocharger, and are two separate components under the vehicle.

Differential Pressure Sensor (DPS) and Pressure Lines

The differential pressure sensor (DPS) (3) measures the pressure difference between the inlet and outlet of the exhaust particulate filter (EPF). When pressure difference has increased above a calibrated threshold, a high particulate loading condition is indicated. The ECM will command a regeneration event in order to restore the filter. If the pressure differential continues to increase across the exhaust filter without a regeneration event, the ECM will illuminate an EPF lamp or send a message to the driver information center (DIC) referring the customer to clean the exhaust filter. To clean the exhaust filter the vehicle must be driven under the conditions necessary for a regeneration to take place. If these lamps and messages are ignored, the ECM will eventually illuminate the malfunction indicator lamp (MIL) and revert to Reduced Engine Power which will require the vehicle to be serviced.

The DPS sensor provides a voltage signal to the ECM on a signal circuit relative to the pressure differential changes in the EPF. The ECM converts the signal voltage input to a pressure value.

The DPS pressure lines (2) are connected before and after the EPF. To provide the pressure sensor with accurate back pressure measurements, the DPS pressure lines should have a continuous downward gradient, without any sharp bends or kinks.

Exhaust Gas Temperature Sensors

The ECM uses two exhaust gas temperature (EGT) sensors to measure the temperature of the exhaust gases at the inlet and outlet of the exhaust particulate filter (EPF). The EGT sensors are variable resistors, when the EGT sensors are cold, the sensor resistance is low, and as the temperature increases, the sensor resistance increases. When sensor resistance is high, the ECM detects a high voltage on the signal circuit. When sensor resistance is low, the ECM detects a lower voltage on the signal circuit. Proper EGTs at the inlet and outlet of the EPF are crucial for proper operation and for initiating the regeneration process. A temperature that is too high in the EPF will cause the EPF substrate to melt or crack. The ECM monitors the temperatures at the EPF inlet and outlet to regulate EPF temperatures.

Intake Air (IA) Valve

The intake air (IA) valve is located upstream of the intake air heater, and is normally in the open position. The ECM commands the valve to close in order to precisely control combustion temperature control during exhaust particulate filter (EPF) regeneration. The IA valve will ensure the temperature of the exhaust gas remains in an efficient range under all operating conditions. The IA valve system uses a position sensor located within the valve assembly to monitor the position of the valve. The IA valve uses a motor to move the valve to a closed position and spring tension returns it to the open position. The motor is operated through Motor Control 1 and 2 circuits.

Exhaust Cooler

The exhaust system has been designed to reduce exhaust gas temperatures during regeneration. The exhaust cooler (4) at the end of the tailpipe draws in cooler air as exhaust gases flow through its openings. The cooler air mixes with the warmer exhaust gas, reducing exhaust gas temperatures at the tailpipe outlet.

Normal Regeneration

Regeneration is the process of removing the captured particulates through incineration within the exhaust particulate filer (EPF). Elevated temperatures are created in the diesel oxidation catalyst (DOC) through a calibrated strategy in the engine control system.

Regeneration occurs when the ECM calculates that the particulate level in the filter has reached a calibrated threshold using a number of different factors, including engine run time, distance traveled, fuel used since the last regeneration, and the exhaust differential pressure. In general, the vehicle will need to be operating continuously at speeds above 48 km/h (30 mph) for approximately 20-30 minutes for a full and effective regeneration to complete. During regeneration the exhaust gases reach temperatures above 550°C (1,022°F). The ECM monitors the EGT sensors during regeneration. If the sensors indicate that regeneration temperatures are exceeding a calibrated threshold, regeneration will be temporally suspended until the sensors return to a normal temperature. If EGT temperatures fall below a normal calibrated threshold, regeneration will be terminated and a corresponding DTC should set. If a regeneration event is interrupted for any reason, it will continue, including the next key cycle, when the conditions are met for regeneration enablement. Normal regeneration is transparent to the customer.

Service Regeneration

A scan tool is an essential tool that is required for service regeneration. Commanding a service regeneration is accomplished using the output control function. The vehicle will need to be parked outside the facility and away from nearby objects, such as other vehicles and buildings, due to the elevated exhaust gas temperature at the tail pipe during regeneration. The service regeneration can be terminated by applying the brake pedal, commanding service regeneration OFF using the scan tool, or disconnecting the scan tool from the vehicle.

Regeneration Process

A number of engine components are required to function together for the regeneration process to be performed. These components are the fuel injectors, turbocharger, IA valve, fuel pressure control, and the intake air heater (IAH).

The regeneration process consists of several stages

Warming up the diesel oxidation catalyst (DOC) to 350°C (662°F) by performing the following

1. Reducing air flow with the intake air valve
2. Increasing or decreasing boost pressure with the turbocharger, depending on engine load
3. Elevating the engine speed
4. Reduce fuel rail pressure
5. Retard fuel injection timing
6. Add late fuel injection pulses. The added fuel is not combusted but is oxidized by the DOC and exhaust particulate filter (EPF) to create heat.

Ash Loading

Ash is a non-combustible by product from normal oil consumption. Low Ash content engine oil (CJ-4 API) is required for vehicles with the exhaust particulate filter (EPF) system. Ash accumulation in the EPF will eventually cause a restriction in particulate filter. Regeneration will not burn off the ash, only particulate matter is burned off. An ash loaded EPF will need to be removed from the vehicle and cleaned or replaced.

Engine Control Module Description

The powertrain has electronic controls to reduce exhaust emissions while maintaining excellent driveability and fuel economy. The engine control module (ECM) is the control center of this system. The ECM monitors numerous engine and vehicle functions. The ECM constantly monitors information from various sensors and other inputs, and controls the systems that affect vehicle performance and 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 malfunction indicator lamp (MIL). When the ECM detects a malfunction, the ECM stores a diagnostic trouble code (DTC). The problem area is identified by the particular DTC that is set. The control module supplies a buffered voltage to various sensors and switches. Review the components and wiring diagrams in order to determine which systems are controlled by the ECM.

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

Scheme 68

Scheme 69

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.

High Idle Switch

The high idle switch will slowly increase engine RPM to the calibrated high idle speed when depressed. The high idle speed can be programmed by using a scan tool. Refer to High Idle Switch Programming . If the High Idle Switch is not operating as desired, refer to High Idle Switch Diagnosis .

Manual High Idle

The diesel engine has a high idle system to improve the warm-up time of the engine in cold weather conditions. This system allows the engine control module (ECM) to increase the idle speed above the normal calibrated value. The ECM increases the idle speed using the following adjustments

1. The fuel injection timing is changed
2. The fuel injection quantity is changed
3. The turbocharger vane position is commanded closed-The vane position will be farther closed than any other normal operating condition.

The instrument panel will indicate the high idle system is active one of two ways

1. The driver information center (DIC) will indicate an active high idle system on light duty trucks.
2. An indicator lamp will flash on medium duty trucks.
3. The manual high idle feature comes enabled from the factory. The Elevated Idle function in the scan tool will disable or enable this feature. If the engine does not increase to the calibrated high idle speed after the procedure is performed, use the scan tool to verify the Elevated Idle speed feature is enabled.

Manual High Idle Speed Enable and Disable

To enable or disable the manual high idle system perform the following procedure

1. Turn the ignition ON, with the engine OFF.
2. Depress the accelerator pedal to the floor and hold down.
3. While the accelerator pedal is depressed, depress the brake pedal 3 times in less than 8 seconds.
4. Release the accelerator pedal.
5. Start the engine.

When the procedure is followed the engine idle speed will slowly increased to the calibrated high idle speed. This is 1,200 RPM for light duty, and 1,500 RPM for medium duty trucks.

The idle speed will return to normal if any of the following conditions occur

1. There is brake, clutch, or throttle input from the driver.
2. The automatic transmission is shifted out of Park or Neutral.
3. The air temperature is more than 7°C (45°F).
4. The engine coolant temperature (ECT) is more than 68°C (154°F).
5. The vehicle speed exceeds 0 km/h (0 mph).

The high idle system will reactivate automatically when the following conditions occur

1. The engine has been idling for more than 30 seconds.
2. The transmission is placed in Park or Neutral.
3. The vehicle speed is 0 km/h (0 mph).
4. The ambient air temperature is less than 3°C (37°F).
5. The ECT is less than 68°C (154°F).
6. The brake, clutch and throttle pedals are not depressed.

Exhaust Gas Recirculation (EGR) System Description

The Exhaust Gas Recirculation (EGR) System is used to reduce the amount of nitrogen oxide (NOx) emission levels caused by high combustion temperatures. At temperatures above 1 371°C (2,500°F), oxygen and nitrogen combine to form oxides of nitrogen (NOx). Introducing small amounts of exhaust gas back into the combustion chamber displaces the amount of oxygen entering the engine. With less oxygen in the air/fuel mixture, the combustion pressures are reduced, and as a result, combustion temperatures are decreased, restricting the formation of NOx.

The EGR valve motor is a direct current (DC) stepper motor utilizing a worm gear that extends from the motor to push on the EGR valve stem. The worm gear is not attached to the valve stem, and can only force the valve open. A return spring is used to force the valve closed.

The mass air flow (MAF) sensor signal is used by the engine control module (ECM) to detect the proper amount of EGR flow. One EGR flow test is performed per ignition cycle. The ECM will close the EGR valve for 5 seconds, then open the EGR valve to 100 percent for 5 seconds. The ECM will then calculate the MAF difference and determine if the proper EGR flow has been detected.

Scheme 70

The exhaust gas recirculation (EGR) valve is controlled by the engine control module (ECM) through the EGR motor high control and EGR motor low control circuits. The ECM supplies voltage that is near ignition voltage to the high and low control circuits at all times. This voltage is used by the ECM as a reference voltage during non EGR operation in order to detect circuit failures. The ECM will pulse width modulate (PWM) the low control circuit to ground and an increase in amperage on the high control circuit can be observed with a DMM when the EGR valve is commanded open. A lower pulse width will increase the open position of the valve. In order to close the EGR valve, the ECM will PWM the high control circuit to ground.

When the ignition is turned ON, the ECM will drive the EGR motor worm gear out with just enough force to touch the EGR valve stem. The ECM will do this 3 times in quick succession. This action determines the minimum closed position of the valve and only happens once per ignition cycle. If the valve is prevented from closing all of the way after the minimum closed position is learned, the scan tool EGR Position parameter will not reflect this position until the next ignition cycle. The EGR motor worm gear is not connected to the EGR valve stem and can only push the valve open. The valve is returned to the closed position by a return spring.

The ECM uses the EGR position sensor to determine the position of the EGR valve. The ECM sends a reference voltage through the 5-volt reference circuit to the EGR position sensor. The ECM provides a voltage return path for the sensor through the low reference circuit. A variable voltage signal, based on the EGR valve position, is sent from the sensor to the ECM through the EGR position sensor signal circuit.

EGR Valve Control Enabling Conditions.

Exhaust gas recirculation (EGR) valve control will only be enabled during idle and cruising conditions while the following conditions are met

1. The intake air temperature (IAT) is more than 5.25°C (41.5°F). EGR valve control will remain enabled until the IAT is less than 0°C (32°F) and will not enable again until the IAT is more than 5.25°C (41.5°F).
2. The engine coolant temperature (ECT) is between 60-96.75°C (140-206.15°F). EGR valve control will remain enabled until the ECT is less than 57°C (134.6°F) or more than 99.75°C (211.55°F) and will not enable again until the ECT is between 60-96.75°C (140-206.15°F).
3. The barometric pressure (BARO) is more than 74 kPa. EGR valve control will remain enabled until the BARO is less than 72 kPa and will not enable again until 74 kPa.

Scheme 71

The fuel tank (6) stores the fuel supply. A mechanical fuel injection pump (9), located below the engine intake, includes the fuel supply pump and the high-pressure pump. Fuel is drawn through the fuel filter/heater element housing (7), which combines a water separator, a hand prime pump, a fuel heater element and a filter element. An integrated hand prime pump is used to prime the fuel system after changing the fuel filter or servicing the fuel system. The mechanical fuel injection pump output is controlled by the ECM, and provides fuel at the pressure needed by the fuel injectors (3). The fuel injectors supply fuel directly to the combustion chambers of the engine. A separate pipe returns unused fuel through a fuel cooler (5) to the fuel tank.

Scheme 72

The fuel tanks store the fuel supply. The primary fuel tank (2) is located on the left side of the vehicle. On vehicles that are equipped with dual fuel tanks, the auxiliary fuel tank is located in the rear of the vehicle. The fuel tanks are each held in place by 2 metal straps that attach to the frame. The fuel tanks are molded from high density polyethylene.

Scheme 73

The fuel filler cap has a torque-limiting device that prevents the cap from being over tightened. To install, turn the cap clockwise until you hear audible clicks. This indicates that the cap is fully seated.

Scheme 74

The fuel sender consists of the following major components

1. The fuel level sensor (1)
2. The fuel strainer (2)

Scheme 75

The auxiliary fuel sender on vehicles equipped with dual fuel tanks consists of the following major components

1. The fuel level sensor (1)
2. The fuel strainer (2)

Fuel Level Sensor

The fuel level sensor consists of a float, a wire float arm, and a ceramic resistor card. The position of the float arm indicates the fuel level. The fuel level sensor contains a variable resistor which changes resistance in correspondence with the amount of fuel in the fuel tank. The engine control module (ECM) sends the fuel level information to the instrument panel cluster (IPC). This information is used for the instrument panel (I/P) fuel gauge and the low fuel warning indicator, if applicable. The ECM also monitors the fuel level input for various diagnostics.

Fuel Strainer

The fuel strainer attaches to the lower end of the fuel sender. The fuel strainer is made of woven plastic. The functions of the fuel strainer are to filter contaminants and to wick fuel. The fuel 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.

Scheme 76

On vehicles equipped with dual fuel tanks, an electric fuel pump is located on the left frame rail. This fuel pump is powered by the fuel pump relay that is controlled by the engine control module (ECM). Fuel is transferred from the auxiliary fuel tank to the primary fuel tank in order to ensure all of the usable fuel volume is available to the fuel injection pump.

Scheme 77

The fuel injection pump is a mechanical high pressure pump. The fuel injection pump is located below the intake manifold. Fuel is pumped to the fuel rails at a specified pressure. Fuel pressure is regulated by a valve on the inlet of the fuel pump, controlled by the engine control module (ECM). Excess fuel from the fuel injection pump returns to the fuel tank through the fuel return pipe and a fuel cooler.

Scheme 78

The fuel filter is located on the rocker cover. The paper filter element traps particles in the fuel that may damage the fuel injection system.

CHANGE FUEL FILTER will appear on the driver information center when a fuel filter change is required.

The fuel filter life monitor uses two control paths consistent with driving conditions. The primary control is based on the accumulated fuel burned, and the secondary control is based on the fuel rail deviations and high pressure pump duty cycle. If the fuel has been contaminated with water or other contaminates, the monitor will see erratic system corrections and display the message or warning lamp. If the fuel filter is not changed when the message or warning light is displayed, then a fuel restriction could occur and cause other diagnostics to fail. The filter life monitor does not drive the diagnostics, but is a result of the restriction.

You must reset the fuel filter life monitor after each fuel filter change. It will not reset itself. Resetting the filter monitor without changing the filter will cause the fuel filter monitor to be inaccurate until the next fuel filter change and reset.

Fuel Heater

The fuel heater is an integrated part of the diesel fuel conditioning module (DFCM). Fuel is heated by passing through the fuel heater element, which is operated by a built-in thermostatic switch. The thermostatic switch turns the heater element ON and OFF, depending on the fuel temperature. The fuel heater element has voltage anytime the ignition is turned ON. The warmed fuel then passes through the fuel filters to the fuel injection pump.

Fuel Feed and Return Pipes

The fuel feed pipe carries fuel from the fuel tank to the fuel filter/heater element housing. The fuel return pipe carries fuel from the fuel rail assemblies back to the fuel tank. The fuel pipes consist of 2 sections

1. The rear fuel pipe assemblies are located from the top of the fuel tank to the chassis fuel pipes. The rear fuel pipes are constructed of steel with sections of rubber hose covered with braiding.
2. The chassis fuel pipes are located under the vehicle and connect the rear fuel pipes to the fuel rail pipes. These pipes are constructed of steel with sections of rubber hose covered with braiding.

Quick-Connect Fittings

Quick-connect fittings provide a simplified means of installing and connecting fuel system components. The fittings consist of a unique female connector and a compatible male pipe end. O-rings, located inside the female connector, provide the fuel seal. Integral locking tabs inside the female connector hold the fittings together.

Fuel Pipe O-Rings

O-rings seal the connections in the fuel system. Fuel system O-ring seals are made of special material. Service the O-ring seals with the correct service part.

Scheme 79

The left and right fuel rail assemblies attach to the cylinder heads. The fuel rail assemblies distribute pressurized fuel to the fuel injectors through the fuel lines.

The fuel rail assemblies consists of the following components

1. The fuel rail pressure sensor in the right fuel rail
2. The fuel pressure relief valve in the left fuel rail

The fuel rail pressure sensor gives the engine control module (ECM) an indication of fuel pressure. The ECM uses this information to regulate fuel pressure, by commanding the fuel pressure regulator open or closed on the inlet of the fuel injection pump.

The fuel pressure relief valve opens only to prevent excessive pressure in the event of a malfunction. Fuel from the fuel pressure relief valve is returned to the fuel tank.

Scheme 80

Scheme 81

A fuel injector is a solenoid device, controlled by the engine control module (ECM), that meters pressurized fuel to a single engine cylinder. Fuel pressure is released from above the fuel injector pintle, and is returned to the fuel tank through the fuel return lines. The difference in fuel pressure above and below the pintle causes the pintle to open. Fuel from the fuel injector tip is sprayed directly into the combustion chamber on the compression stroke of the engine.

The control functions for the fuel injection system are integrated in the ECM. During the manufacturing process, each injector's flow rate is measured and recorded as injection quantity adjustment (IQA) flow rate data. The flow rate data is then etched as a hexadecimal number on the body of the injector. This data, together with the injector's cylinder position, is stored in the memory of both the glow plug control module (GPCM) and the ECM. When the ignition is turned ON, both the GPCM and the ECM monitor to ensure that the fuel injection flow rate numbers are present. If any of the injector flow rate numbers are missing, the diagnostic for that control module will set the appropriate DTC.

Scheme 82

The fuel system cooler (1) is located in front of the primary fuel tank. The fuel system cooler cools the fuel before it is returned to the fuel tank.

Glow Plug System Description

In the diesel engine, air alone is compressed in the cylinder. Then, after the air has been compressed, a charge of fuel is sprayed into the cylinder and ignition occurs, due to the heat of compression. Eight glow plugs are used as an aid to starting.

Control of the instant start system (ISS) glow plugs is accomplished by a glow control module unit and 4.7 volt glow plugs, requiring 2 seconds to heat up to 1,000°C (1,832°F). The temperature and the power consumption is controlled between the engine control module (ECM) and the controller within a wide range to suit the engine's pre-heating requirements. Each glow plug is energized individually. This capability yields more optimum heat times for the glow plugs, thus pre-glow times can be kept to a minimum for short wait to crank times and maximum glow plug durability. A DTC will set if there is a glow plug system fault.

A normal functioning system operates as follows

1. Turn the ignition ON with the engine OFF, and at room temperature.
2. The glow plugs turn ON and heat up in 2 seconds and then are pulse-width modulated (PWM) for another 2 seconds.
3. The glow plug wait lamp is ON for 1 second during cold start.
4. The glow plug wait lamp may not illuminate during a warm engine start.
5. If the engine is cranked during or after the above sequence, the glow plugs may cycle ON and OFF after the ignition switch is returned from the start position, whether the engine starts or not. The engine does not have to be running to terminate the glow plug cycling.

The glow plug initial ON time will vary based on the system voltage and temperature. Lower temperatures cause longer ON times.

The ECM provides glow plug operation after starting a cold engine. This post-start operation is initiated when the ignition switch is returned to Run, from the Start position. This function helps clean up excessive white smoke and/or poor idle quality after starting.

Glow Plugs

The glow plugs are 4.7 volt heaters in each of the cylinders that turn ON, then pulse-width modulated when the ignition switch is turned to the RUN position prior to starting the engine. They remain pulsing a short time after starting, then they are turned OFF.

A Wait to Start lamp on the instrument panel provides information on engine starting conditions. The Wait to Start lamp will not illuminate during post-start glow plug operation.

Glow Plug/Controller

The glow plug controller is a solid state device which operates the glow plugs. The glow plug controller is connected to the following circuits

1. The fuel heater ignition 1 voltage circuit
2. The battery voltage circuit
3. The CAN communication circuit located between the engine control module (ECM) and the glow plug controller
4. The engine ground circuit
5. The glow plug supply voltage circuits located between the glow plug controller and the glow plugs.

The glow plug diagnostic circuits are directly monitored individually by using a separate transistor to control current to each glow plug. Individual diagnosis is thus possible for every glow plug.

Intake Air Heater System Description

The intake air heater (IAH) is located in the air inlet tube and is used to warm the incoming air to aid in starting the engine and for proper cylinder combustion. The glow plug control module (GPCM) will command the IAH on when the engine coolant temperature is below 40°C (104°F).

The IAH is commanded ON by the GPCM through the command 1 circuit and the command 2 circuits. The command 1 signal is ON or OFF from the GPCM to the IAH. The command 2 circuits are digital signal from the GPCM to the IAH. Without both signals the IAH will not operate. The feedback signal is digital and informs the GPCM of the status of IAH. The temperature, current, and voltage circuits are analog signals from the IAH to the GPCM.

The IAH will be commanded to 100 percent when the engine coolant temperature is below 5°C (41°F) for 180 seconds after key up, then it will ramp down to 42 percent after 180-300 seconds and will hold it there until 300-500 seconds. After 500-600 seconds the IAH will ramp down to 0 percent. When the engine coolant is 10-40°C (50-104°F) the IAH is 100 percent for 30 seconds after key up then ramps down to 42 percent after 30-90 seconds and holds it there for up to 500 seconds, then it ramps down to 0 percent from 500-600 seconds.

Scheme 83

Scheme 84

Scheme 85

Scheme 86

The turbocharger increases engine power by pumping compressed air into the combustion chambers, allowing a greater quantity of fuel to combust at the optimal air/fuel ratio. The turbine spins as exhaust gas flows out of the engine and over the turbine blades, and turns the compressor wheel at the other end of the turbine shaft, pumping more air into the intake system.

The engine control module (ECM) controls nine vanes for the turbocharger. The vanes are used to vary the amount of boost pressure and can control the boost pressure independent of engine speed. The vanes mount to a unison ring which are rotated to change the vane angle. The ECM will vary the vane angle which adjusts the boost dependent upon the load requirements of the engine.

The turbocharger vanes are normally open when the engine is not under load. However, the ECM will often close the turbocharger vanes to create back pressure to drive exhaust gas through the exhaust gas recirculation (EGR) valve as required. At extreme cold temperatures, the ECM may close the vanes at low load conditions in order to accelerate engine coolant heating. The ECM may also close the turbocharger vanes under exhaust braking conditions, only with RPO K40.

During regeneration, the ECM will vary the turbocharger vanes to assist with the exhaust system warm-up, and to maintain proper engine exhaust temperatures needed to properly regenerate the exhaust particulate filter (DPF).

The turbocharger control system utilizes the following components

Turbocharger Vane Position Control Solenoid Valve

The vane position control solenoid valve (2) works in conjunction with oil pressure to control the turbocharger vanes. The ECM uses a pulse width modulation on both control circuits to control the solenoid valve. The solenoid valve allows the engine oil pressure to move a piston. This piston rotates the unison ring, thus controlling the engine boost dependant upon engine load.

Turbocharger Vane Position Sensor

The ECM uses the turbocharger vane position sensor to monitor the TC vane angle. The voltage is low when the TC vanes are open, and high when the TC vanes are closed.

See also:
• High Idle Switch Programming
• High Idle Switch Diagnosis