Engine Controls - 6.6L - Introduction (2 of 2): Overview GMC Sierra 1500

Very Cold Weather Operation

If the vehicle is driven in very cold temperatures and can not get a winterized Number 2-D that has been adapted to cold weather or a Number 1-D, use one gallon of kerosene for every 2 gallons of diesel fuel. Once you add kerosene, run the engine for several minutes to mix the fuels. Only add kerosene when the temperature falls below -18°C (0°F), because the fuel economy and lubricating qualities of kerosene is not as good as that of diesel fuel.

In cold weather, the fuel filter may become clogged (waxed). To unclog the filter, move the vehicle to a warm garage area and warm the filter to a temperature between 0-10°C (32-50°F). Replacing the filter is not necessary.

If the vehicle is driven in very cold temperatures and can not get a winterized Number 2-D that has been adapted to cold weather or a Number 1-D, use one gallon of kerosene for every 2 gallons of diesel fuel. Once you add kerosene, run the engine for several minutes to mix the fuels. Only add kerosene when the temperature falls below -18°C (0°F), because the fuel economy and lubricating qualities of kerosene is not as good as that of diesel fuel.

In cold weather, the fuel filter may become clogged (waxed). To unclog the filter, move the vehicle to a warm garage area and warm the filter to a temperature between 0-10°C (32-50°F). Replacing the filter is not necessary.

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. IMPORTANT: Twisted-pair wires provide an effective shield that helps protect sensitive electronic components from electrical interference. If the wires were covered with shielding, install new shielding. In order to prevent electrical interference from degrading the performance of the connected components, you must maintain the proper specification when making any repairs to the twisted-pair wires shown : The wires must be twisted a minimum of 9 turns per 31 cm (12 in) as measured anywhere along the length of the wires The outside diameter of the twisted wires must not exceed 6.0 mm (0.25 in)

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Circuit/System Description

The control functions for the fuel injection system are integrated in the engine control module (ECM). Each injector's flow rate information and cylinder position are stored in the memory of both the glow plug control module (GPCM) and the ECM. The fuel injector flow rate programming must be done when any of the following procedures are performed

1. The ECM is replaced
2. The GPCM is replaced
3. Any fuel injectors are replaced

If the ECM does not communicate, the flow rate information can be retrieved from the GPCM. If both control modules fail to communicate, the fuel injector flow rate information, or injection quantity adjustment (IQA) flow rate numbers, will need to be retrieved from each individual injector.

Engine Control Module (ECM) 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 at the information from various sensors and other inputs, and controls the systems that affect vehicle performance and emissions. The ECM also performs the 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

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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.

Accelerator Pedal Position (APP) System Description

The accelerator pedal position (APP) system along with the vehicle electronics and components is used to calculate and control the amount of acceleration and deceleration via fuel injector control. This eliminates the need for a mechanical cable attachment from the accelerator pedal to a throttle body.

The APP system includes, but is not limited to, the following components

1. The APP sensor assembly
2. The engine control module (ECM)

Fuel System Description

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.

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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.

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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.

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The fuel sender consists of the following major components

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

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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)

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 an electronic glow plug control 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.
4. 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.

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.

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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.

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).

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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.

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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. In a conventional turbo, the turbine (4) spins as exhaust gas flows out of the engine and over the turbine blades. This spins the compressor wheel at the other end of the turbine shaft, pumping more air into the intake system.

The turbocharger for this system has vane position control by the engine control module (ECM). The vanes (5) are controlled to vary the amount of boost pressure. Thus, the boost pressure can be controlled independent of engine speed. There are 9 controllable vanes in this turbocharger. The vanes mount to a unison ring (3) that can be rotated to change the vane angle. The ECM will vary the boost dependent upon the load requirements of the engine.

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.

The turbocharger control system utilizes the following components