General Motors in vehicle Local Area Network (GMLAN) is a family of serial communication buses (subnets) which enable Electronic Control Units (ECUs or nodes) to communicate with each other, or with a diagnostic tester.

GMLAN supports three buses, a dual wire high speed bus, a dual wire mid speed bus, and a single wire low speed bus.

The decision to use a particular bus in a given vehicle depends upon how the feature/functions are partitioned among the different ECUs in that vehicle.GMLAN buses use the Controller Area Network (CAN) communications protocol. Data is packaged into CAN messages, which are segmented into CAN ‘frames’. Each CAN frame includes header data (also known as the CAN Identifier, or CANId), and a maximum of eight (8) data bytes. A message may be comprised of a single frame, or multiple frames depending on the number of data bytes which defines the complete message. Data link arbitration occurs only over the header, or CANId, portion of a frame.

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 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.

The malfunction indicator lamp (MIL) is located in the instrument panel cluster. The MIL indicates that an emissions related fault has occurred.

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 fuel injection system.

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

The accelerator pedal position (APP) sensor is mounted on the accelerator pedal control assembly. The sensor is made up of 2 individual sensors within one housing. Two separate signal, low reference, and 5-volt reference circuits are used in order to interface the accelerator pedal sensor assembly with the ECM. Each sensor has a unique functionality to determine pedal position. The ECM uses the APP sensor to determine the amount of acceleration or deceleration desired by the person driving the vehicle. The APP sensor 1 voltage should increase as the accelerator pedal is depressed, from about 1.0 volt at 0 pedal travel to about 4 volts at 100 percent pedal travel. APP sensor 2 voltage should increase from about 0.5 volts at 0 pedal travel to about 2.0 volts at 100 percent pedal travel.

The fuel system of this vehicle is consists of the followings:

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 gage and the low fuel warning indicator, if applicable. The ECM also monitors the fuel level input for various diagnostics.

A main fuel supply pump is located on the left half of the fuel tank. This fuel pump is powered by the fuel pump relay that is controlled by the engine control module (ECM). Fuel is transferred from the fuel tank to the fuel injection pump.

The CP1H high-pressure fuel injection pump from Bosch is used on the Z20S diesel engine. The pump is an enhanced version of the CP1. The pump now provides a rail system pressure of up to 1600 bar. This was achieved by reinforcing the drive gear, modifying the valve units and taking measures to increase the strength of the housing. To ensure a sufficient quantity of fuel, the pump is designed so that it can achieve an overall delivery rate of 160 l/h.

The required delivery rate is steplessly regulated by the electrically actuated metering unit located on the fuel injection pump. This valve adapts the quantity of fuel delivered to the rail to the system's requirements. This type of fuel delivery control not only reduces the pump's power requirements but also reduces the maximum fuel temperature. The admission pressure required for the fuel injection pump is provided by an electrically operated fuel supply pump located in the fuel tank. Excess fuel from the fuel injection pump returns to the fuel tank through the fuel return pipe.

The fuel injection pump is a triple-action piston pump. It forms the interface between the low-pressure side and the high-pressure side. It is driven via the engine timing belt.

The fuel filter assembly consists of the fuel filter housing, fuel filter element, water in fuel sensor, fuel heater, and fuel temperature sensor. The filter element traps particles in the fuel that may damage the fuel injection system. The engine control module (ECM) receives a fuel temperature signal from the fuel temperature sensor and heats the fuel through the fuel heater. The water in fuel sensor senses the presence of the water in the fuel filter housing.

The fuel feed pipe carries fuel from the fuel tank to the fuel injection pump. The fuel return pipe carries fuel from the fuel return junction block back to the fuel tank.

The fuel rail assembly distributes pressurized fuel to the fuel injectors through the fuel lines.

The fuel rail assembly consists of the following components:

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 along with the metering unit on the inlet of the fuel injection pump.

A fuel injector is a solenoid device, controlled by the engine control module (ECM), which meters pressurized fuel to a single engine cylinder. The ECM energizes the low-impedance injector solenoid to open a normally closed valve. 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.

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. Four glow plugs are used as an aid to starting.

Control of the glow plugs is accomplished by a glow control unit (GCU) and glow plugs, requiring maximum 3 seconds to heat up to 1,000°C (1,832°F). The temperature and the power consumption are controlled between the engine control module (ECM) and the GCU 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.

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

The glow plugs are 4.4 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 glow plug indicator on the instrument panel provides information on engine starting conditions. The glow plug indicator will not illuminate during post-start glow plug operation.

The glow control unit is a solid state device which operates the glow plugs. The GCU is connected to the following circuits:

The exhaust gas recirculation (EGR) system is used to reduce the amount of nitrogen oxide (NOx) emission levels caused by high combustion temperatures. It does this by introducing small amounts of exhaust gas back into the combustion chamber. The exhaust gas absorbs a portion of the thermal energy produced by the combustion process and thus decreases combustion temperature. The EGR system will only operate under specific temperature, barometric pressure and engine load conditions in order to prevent drivability concerns and to increase engine performance.

The EGR system consists of the following components:

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 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 vehicle has vane position control by the engine control module (ECM). The vanes are controlled to vary the amount of boost pressure. Thus, the boost pressure can be controlled independent of engine speed. The vanes mount to a unison ring that can be rotated to change the vane angle. The ECM will vary the boost dependent upon the load requirements of the engine.

The diesel after-treatment system consists of an under hood pre-catalytic converter (Precat) and an underbody catalytic converter (Main Diesel Oxidation Catalyst + Coated Diesel Particulate Filter).

Engine control technology and diesel after-treatment system are designed to reduce exhaust emissions such as hydrocarbons (HC), carbon monoxide (CO) and particulates to meet the today’s enhanced emission regulations.

The diesel particulate filter is made from Silicon Carbide and is coated with noble metal. It is designed to reduce hydrocarbons (HC) and carbon monoxide (CO) emissions and to collect particulates from the engine exhaust to minimize discharge of soot to the atmosphere. The soot particles accumulate in the channels of the coated diesel filter and are burned off at regular interval (through a process called "regeneration") to prevent filter from clogging. Excess soot in filter can cause drop in engine performance and crack the filter during regeneration. During regeneration, additional fuel is injected via multiple post injections to increase the exhaust gas temperature. During this period, the DPF temperature is raised to approximately 600°C and the deposited soot is oxidized or burned off to carbon-dioxide (CO2).

The pressure pipes, which are connected to the differential pressure sensor, measure the level of soot deposit in the coated diesel particulate filter and protect the engine by triggering regeneration when critical soot level is detected in the filter.

Under hood pre-catalyst (Precat) and main diesel oxidation catalyst (DOC) are coated with noble metal and have the function of reducing hydrocarbons (HC) and carbon monoxide (CO) emissions. Also, during regeneration, these components help to increase the exhaust gas temperature by burning the post injected fuel. The in-cylinder post injection allows filter regeneration to occur over the entire engine operating range as well as under all ambient temperature and pressure conditions. The regeneration process is smooth and essentially transparent to the driver of the vehicle.