GMLAN serial data interface
The General Motors Local Area Network (GMLAN) of a vehicle is a family of serial communication buses (subnets) that allow electronic control devices (ECU or nodes) maintain communication with each other or with the diagnostic tester.
GMLAN supports three buses, a high-speed two-wire bus, a medium-speed two-wire bus, and a single-wire low-speed bus.
- High speed tire (500 kbps) - usually used to share real-time data such as driver-specified torque, actual engine torque, steering angle, etc.
- Medium speed tire (approximately 95.2 kbps) - usually used for information support (display, navigation, etc.), where system response time requires that a large amount of data be transmitted in a relatively short time, such as updating the display of graphical information.
- Low speed tire (33.33 kbps) - typically used for driver-controlled devices where a system response time of 100-200 ms is required. This bus also supports high-speed operation at 83.33 kbps, used only when reprogramming the ECU.
The decision to use a particular bus on a particular vehicle depends on how the functions are distributed among the various controllers 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 CAN identifier, or CANId) and a maximum of eight (8) bytes of data. A message may consist of a single frame or multiple frames, depending on the number of data bytes that define the complete message. Channel arbitration occurs only on the header, or CANId, portion of the frame.
Description of the electronic engine management system (ECM) controller
The powertrain includes electronic control systems designed to reduce emissions while maintaining excellent drivability and fuel economy. The engine control module (ECM) is the control center of this system. The ECM controls many engine and vehicle functions. The ECM continuously receives information from various sensors and other data sources, and controls systems that affect vehicle performance and emissions. The ECM also performs diagnostic tests on various parts of the system. The ECM can detect malfunctions and alert the driver via the Malfunction Indicator Lamp (MIL). When a malfunction is detected, the ECM stores a diagnostic trouble code (DTC) that identifies the system that is malfunctioning. The ECM supplies buffered power to various sensors and switches. To determine which systems are controlled by the ECM, it is necessary to review the components and electrical circuits.
Malfunction Indicator Lamp (MIL) Operation
The Malfunction Indicator Lamp (MIL) is located in the instrument cluster. The MIL indicates that an emission-related malfunction has occurred.
Description of the Accelerator Pedal Position (APP) Monitoring System
The accelerator pedal position (APP) control system, together with the vehicle's electronic systems and other components, calculates and controls the amount of acceleration and deceleration by controlling the fuel injection. This eliminates the need for a mechanical connection via a cable between the accelerator pedal and the fuel injection system.
Among other things, the APP system includes the following nodes:
- Accelerator Pedal Position (APP) Sensor Assembly
- Electronic Engine Management System (EEMS) Controller
Accelerator Pedal Position (APP) Sensor
The accelerator pedal position (APP) sensor is located on the accelerator pedal assembly. The sensor consists of 2 separate sensors in a single housing. The accelerator pedal position sensor communicates with the ECM using two separate signal circuits, a low reference and a 5-volt reference. Each sensor has a different function to determine the position of the pedal. The ECM uses the APP sensor to determine the amount of acceleration or deceleration desired by the driver of the vehicle. The voltage from APP sensor 1 increases as the accelerator pedal is depressed from approximately 1.0 V at 0% pedal travel to 4.0 V at 100% pedal travel. The voltage from APP sensor 2 increases from approximately 0.5 V at 0% pedal travel to 2.0 V at 100% pedal travel.
Description of the fuel system
The fuel system of this vehicle includes the following components:
- Low pressure circuit
- Supply and return pipes and hoses
- Return fuel distribution block
- Fuel tank
- Fuel supply pump
- Fuel level sensors
- Fuel filter/heater
- Water in Fuel (WIF) Sensor
- High pressure circuit
- High pressure fuel pump with metering unit
- Fuel rail (Common Rail)
- Fuel Rail Pressure (FRP) Sensor
- Fuel injectors
- Fuel Rail Pressure Regulator (FRP)
Fuel level sensor
The fuel level sensor consists of a float, a wire float arm and a ceramic resistor board. The fuel level is determined by the position of the float arm. The fuel level sensor has a variable resistor whose resistance changes depending on the amount of fuel remaining in the tank. The engine control module (ECM) sends fuel level information to the instrument cluster (IPC). This information is used to display the fuel level indicator on the instrument cluster and the low fuel warning indicator (if available). In addition, the input from the fuel level sensor is used by the ECM for various diagnostic functions.
Fuel supply pump
The main fuel supply pump is located on the left half of the fuel tank. Power is supplied to this fuel pump from the fuel pump relay, which is controlled by the ECM. Fuel is pumped from the fuel tank to the high-pressure fuel pump.
High pressure fuel pump (CP1H)
The BOSCH CP1H high-pressure fuel pump is used on the Z20S diesel engine. This pump is an improved version of the CP1 model. Now this pump creates a pressure of up to 1600 bar in the fuel rail. This was achieved by strengthening the drive, improving the valve units and taking measures to increase the strength of the housing. To ensure sufficient fuel, the pump has a design with a total capacity of 160 l / h.
The required pump output is continuously adjusted by means of an electrically driven metering unit located on the high-pressure fuel pump. This valve regulates the amount of fuel supplied to the rail in accordance with the system's needs. This type of fuel supply regulation not only reduces the pump power requirements, but also reduces the maximum fuel temperature. The inlet pressure required for the high-pressure fuel pump is provided by an electrically driven fuel supply pump located on the fuel tank. Excess fuel from the high-pressure fuel pump is returned to the fuel tank via the return fuel line.
The high-pressure fuel pump is a triple-acting piston pump. It connects the low-pressure and high-pressure fuel circuits. The pump is driven by the engine via the timing belt.
Fuel filter assembly
The fuel filter assembly consists of a fuel filter housing, filter element, water-in-fuel sensor, fuel heater, and fuel temperature sensor. The filter element traps particles in the fuel that could damage the fuel injection system. The fuel temperature sensor sends a signal to the ECM, which commands the fuel heater to heat the fuel. The water-in-fuel sensor detects the presence of water in the fuel filter housing.
Fuel supply and return lines
The supply fuel lines deliver fuel from the fuel tank to the high-pressure fuel pump. The return fuel lines return fuel from the return fuel distribution unit back to the fuel tank.
Fuel rail assemblies
The fuel rail assembly distributes fuel under pressure through the fuel lines to the fuel injectors.
The fuel rail assembly consists of the following parts:
- Fuel rail (Common Rail)
- Fuel Rail Pressure (FRP) Sensor
- Fuel Rail Pressure Regulator (FRP)
The fuel rail pressure sensor provides fuel pressure information to the ECM. The ECM uses this information to regulate fuel pressure by commanding the opening or closing of the fuel pressure regulator together with the metering unit at the inlet of the high-pressure fuel pump.
Fuel injectors
A fuel injector is an electromagnetic device controlled by an ECM controller that dispenses compressed fuel to a separate engine cylinder. From the ECM controller, voltage is applied to the low-impedance solenoid valve of the nozzle to open the normally closed valve. Pressurized fuel is discharged over the fuel injector needle and returned to the fuel tank via return fuel lines. The difference in fuel pressure above and below the needle causes the needle to open. Fuel from the fuel nozzle tip is sprayed directly into the combustion chamber during the compression stroke of the engine.
Description of the glow plug system
In a diesel engine, only air is compressed in the cylinder. Then, after the air is compressed, a portion of fuel is sprayed into the cylinder, and the resulting heat from compression causes ignition. Four glow plugs are used to facilitate starting the engine.
The glow plugs are controlled by the glow plug controller (GCU), and the glow plugs require no more than 3 seconds to reach 1000°C (1832°F). Temperature and power consumption are controlled jointly by the ECM and GCU over a wide range to achieve engine preheat conditions. Each glow plug is powered separately. This arrangement ensures optimum glow plug heating time, while preheat operation time can be minimized to reduce starting time and extend glow plug life.
The initial glow plug turn-on time varies depending on system voltage and temperature. At low temperatures, the turn-on time increases.
Glow plugs
The glow plugs are heaters in each cylinder that operate at 4.4 volts. They are switched on and controlled by a pulse-width-modulated signal when the ignition key is turned to the RUN position before starting the engine. They continue to operate in a pulsed mode for a short time after starting, and then switch off.
The glow plug indicator on the instrument panel serves to inform about the engine starting conditions. The spark plug indicator does not light during glow plug operation after the engine has started.
Glow Plug Controller (GCU)
The glow plug controller is a semiconductor device that controls the glow plugs. The GCU controller is connected to the following circuits:
- Ignition voltage circuit 1.
- Battery voltage circuit.
- Diagnostic circuit located between the ECM and the glow plug controller.
- Engine ground chain.
- The glow plug power circuits are located between the glow plug controller and the glow plugs themselves.
Description of the Exhaust Gas Recirculation (EGR) System
The exhaust gas recirculation (EGR) system serves to reduce the nitrogen oxide (NOx) content in the exhaust gases formed at high combustion temperatures. This is done by feeding a small amount of exhaust gases back into the combustion chamber. The exhaust gases absorb some of the heat energy generated during combustion and thus reduce the combustion temperature. The EGR system only operates at certain values of temperature, barometric pressure and engine load in order to prevent deterioration in driving performance and increase engine power.
The EGR system consists of the following components:
- EGR valve - The EGR valve is vacuum operated. The EGR valve is used to direct exhaust gases from the exhaust system to the intake manifold for recirculation during combustion.
- Vacuum pump - The vacuum for the EGR valve vacuum actuator is created by a camshaft driven mechanical pump called a vacuum pump. The vacuum pump operates continuously when the engine is running.
- EGR valve vacuum actuator control solenoid valve - The EGR valve vacuum actuator control solenoid valve is located in the EGR vacuum control system between the vacuum pump and the EGR valve. The ECM outputs a pulse width modulation (PWM) signal via the EGR valve vacuum actuator control solenoid valve ground circuit to open the EGR valve to the desired position using a metered supply of vacuum from the vacuum pump. The EGR valve vacuum actuator control solenoid valve receives ignition voltage via the ignition voltage circuit 1 from the main relay. The EGR valve vacuum actuator control solenoid valve is of the normally closed type.
- EGR Throttle Actuator Control - Diesel engines do not create enough vacuum to allow recirculated exhaust gases to enter the combustion process on their own. The EGR throttle valve, when closed, prevents fresh air from entering the engine, causing a vacuum to be created in the engine. When the ECM commands the EGR valve to open, the EGR throttle valve is commanded to close. The EGR throttle valve is of the normally open type.
- MAF sensor - MAF sensor (mass air flow) is located in the intake air system between the air cleaner and the outlet port of the EGR valve. The ECM uses the signal from the mass air flow (MAF) sensor to calculate the actual flow of recirculated exhaust gases in the intake manifold. When the EGR valve is open, the MAF value decreases.
- EGR cooler - Engine coolant flows through the EGR cooler to reduce the temperature of the exhaust gases before they enter the EGR valve and intake manifold.
Description of the turbocharging system
A turbocharger increases engine power by forcing compressed air into the combustion chambers, allowing more fuel to be burned with the optimum fuel-air mixture. In a conventional turbocharger, the turbine is spun by exhaust gases from the engine hitting the turbine blades. This causes the compressor wheel at the opposite end of the turbine shaft to spin, forcing more air into the intake system.
In this car's turbocharger, the turbine blades are controlled by the engine control module (ECM), which regulates the turbo boost pressure. Thus, the boost pressure can be adjusted independently of the engine speed. The blades are mounted on a common ring, which can rotate to change the angle of the blades. The ECM changes the boost depending on the engine load.
Description of the Diesel Particulate Filter (DPF) System
The diesel engine exhaust gas treatment system consists of a starting catalyst (precat) located in the engine compartment and a catalytic converter located under the body (main diesel oxidizing catalyst + coated diesel particulate filter).
Engine management and exhaust gas treatment systems are designed to reduce the content of harmful substances such as hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gases, as well as particulate matter (soot) in order to comply with today's stringent exhaust gas toxicity standards.
The diesel particulate filter is made of silicon carbide and coated with a noble metal. It is designed to reduce hydrocarbons (HC) and carbon monoxide (CO) and traps particles in the engine exhaust to reduce soot emissions into the atmosphere. Soot particles accumulate in the coated diesel filter channels and are burned off at regular intervals (in a process called "regeneration") to prevent the filter from clogging. Excessive soot accumulation in the filter can lead to a loss of engine power and filter failure during regeneration. To increase the exhaust gas temperature during regeneration, additional fuel is injected into the filter through multiple injectors. During this time, the temperature in the DPF rises to approximately 600°C and the accumulated soot is oxidized or burned off, turning into carbon dioxide (CO₂).
Pressure tubes connected to a differential pressure sensor are used to measure the level of soot deposits in the coated diesel particulate filter and protect the engine by initiating a regeneration process when a critical level of soot deposits is reached.
The pre-catalytic converter in the engine compartment (precat) and the main diesel catalytic converter (DOC) are coated with a noble metal and serve to reduce the content of hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gases. In addition, during regeneration, these units help to increase the exhaust gas temperature by burning additionally injected fuel. Additional fuel injection into the cylinders allows regeneration to be performed under any engine operating conditions, as well as at any values of outside temperature and pressure. The regeneration process occurs smoothly and is usually unnoticeable for the driver of the car.
The article is based on data from the website: ChevyMan