Serial data interface GMLAN
General Motors LAN (GMLAN) car - a family of serial communication buses (subnets), which allow electronic control devices (ECU or nodes) communicate 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 bus (500 kbps) - typically 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 informational support (display, navigation, etc.), where the response time of the system requires that a large amount of data be transmitted in a relatively short time, such as updating the display of graphical information.
- low speed bus (33.33 kbps) - typically used for driver-controlled devices where a system response time of the order 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 specific bus on a particular vehicle depends on how the functions are distributed among the various controllers of that vehicle. GMLAN buses use the controller LAN communication protocol (CAN). The data is packed into CAN·messages, which are segmented into "frames" CAN. Each CAN frame includes header data (also known as the 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. Link arbitration occurs only on the header, or CANId, part of the frame.
Description of the electronic engine management system controller (ECM)
The power plant has electronic control systems designed to reduce exhaust emissions while maintaining excellent driving performance and fuel economy. Electronic engine management controller (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. In addition, the ECM performs diagnostic checks on various parts of the system. The ECM can detect malfunctions and warn the driver through a malfunction indicator lamp (MIL). When a malfunction is detected, the ECM stores a DTC (DTC), which identifies the system in which the fault occurred. The controller supplies buffered supply voltage to various sensors and switches. To determine which systems are controlled by the ECM, you need to consider the components and wiring diagrams.
Malfunction indicator lamp operation (MIL)
Malfunction indicator lamp (MIL) located on the instrument cluster. The MIL indicates that an emission problem has occurred.
Description of the accelerator pedal position control system (APP)
Accelerator Pedal Position Control System (APP) together with the vehicle's electronic systems and other components, it is used to calculate and control the amount of acceleration and deceleration by controlling the fuel injection. Thus, there is no need for a mechanical connection by means of a cable between the accelerator pedal and the fuel injection system.
Among other things, the APP system includes the following nodes:
- Accelerator Pedal Position Sensor Assembly (APP)
- Electronic engine management controller (ECM)
Accelerator pedal position sensor (APP)
Accelerator pedal position sensor (APP) located on the accelerator pedal assembly. The sensor consists of 2 separate sensors in one housing. The accelerator pedal position sensor communicates with the ECM using two separate signal circuits, a low reference and a 5V reference. Each sensor performs a different function to detect pedal position. The ECM uses the APP sensor to determine the amount of acceleration or deceleration required by the driver of the vehicle. The voltage from the APP sensor 1 increases when the accelerator pedal is depressed from approximately 1.0V at 0% pedal travel to 4.0V at 100% pedal travel. The voltage from the APP 2 sensor rises from approximately 0.5V at 0% pedal travel to 2.0V at 100% pedal travel.
Description of the fuel system
The composition of the fuel system of this car 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 sensor (WIF)
- High pressure circuit
- High pressure fuel pump with dosing unit
- fuel rail (Common Rail)
- Fuel rail pressure sensor (FRP)
- fuel injectors
- Fuel rail pressure regulator (FRP)
Fuel level sensor
The fuel level sensor consists of a float, a float wire arm and a ceramic resistor board. The fuel level is determined by the position of the float lever. The fuel level sensor has a variable resistor, the resistance of which changes depending on the amount of fuel left in the tank. From the controller of the electronic engine management system (ECM) information about the fuel level is transmitted to the instrument cluster (IPC). This information is used to indicate the remaining fuel gauge on the instrument panel, as well as for the low fuel warning indicator (if available). In addition, input from the fuel level sensor is used by the ECM for various diagnostic functions.
Fuel supply pump
The main fuel feed pump is located on the left side 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 assemblies and taking measures to increase the strength of the housing. In order to provide enough fuel, the pump is designed to have a total capacity of 160 l/h.
The required output of the pump is infinitely adjustable 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 according to the needs of the system. This type of fuel control not only reduces pump power requirements, but also reduces the maximum fuel temperature. The intake pressure required by the high pressure fuel pump is provided by an electric fuel feed pump located on the fuel tank. Excess fuel from the high pressure fuel pump is returned to the fuel tank through the fuel return line.
The high pressure fuel pump is a triple acting piston pump. It links the low and high pressure fuel circuits. The pump is driven from the engine by a timing belt.
Fuel filter assembly
The fuel filter assembly consists of a fuel filter housing, a filter element, a water-in-fuel sensor, a fuel heater, and a fuel temperature sensor. The filter element traps particles in the fuel that can damage the fuel injection system. From the fuel temperature sensor, the signal is sent to the ECM, which issues a command to heat the fuel through the fuel heater. The water in fuel sensor detects the presence of water in the fuel filter housing.
Supply and return fuel lines
The fuel supply lines carry fuel from the fuel tank to the high pressure fuel pump. Fuel return lines return fuel from the return fuel distribution unit back to the fuel tank.
Fuel Rail Assemblies
The fuel rail assembly distributes pressurized fuel through the fuel lines to the fuel injectors.
The fuel rail assembly consists of the following parts:
- fuel rail (Common Rail)
- Fuel rail pressure sensor (FRP)
- Fuel rail pressure regulator (FRP)
The fuel rail pressure sensor provides fuel pressure information to the ECM. The ECM uses this information to control fuel pressure by opening or closing the fuel pressure regulator along with the metering block upstream of the high pressure fuel pump.
Fuel injectors
The fuel injector is an electromagnetic device controlled by the ECM that dispenses compressed fuel into a single engine cylinder. The ECM energizes the low impedance injector solenoid valve to open the normally closed valve. Pressurized fuel is discharged over the fuel injector needle and returned to the fuel tank through the fuel return lines. The difference in fuel pressure above and below the needle causes the needle to open. Fuel from the fuel injector tip is sprayed directly into the combustion chamber during the engine's compression stroke.
Description of the glow plug system
In a diesel engine, only air is compressed in the cylinder. Then, after compressing the air, a portion of the fuel is sprayed into the cylinder, and as a result of the heating during compression, ignition occurs. 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 take no more than 3 seconds to heat up to 1000°C (1832°F). Temperature and power consumption are controlled jointly by the ECM and GCU over a wide range to meet engine preheat conditions. Power is supplied to each glow plug separately. Such an arrangement provides optimum glow plug heating time, while the preheat operation time can be kept to a minimum to reduce start-up time and extend the life of the glow plugs.
The initial glow plug ignition time varies depending on system voltage and temperature. At low temperatures, the turn-on time increases.
Glow plugs
Glow plugs are heaters in each cylinder that operate at 4.4 volts. They are turned on and controlled by a pulse-width modulated signal when the ignition key is turned to "JOB" before starting the engine. For some time after starting, they continue to work in a pulsed mode, and then turn off.
The glow plug indicator on the instrument panel is used to inform you about the conditions for starting the engine. The spark plug indicator does not light up while the glow plugs are operating after the engine is started.
Glow plug controller (GCU)
The glow plug controller is a semiconductor device that controls the glow plugs. The GCU 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 circuit.
- The glow plug supply circuits are located between the glow plug controller and the glow plugs themselves.
Description of the exhaust gas recirculation system (EGR)
Exhaust gas recirculation system (EGR) serves to reduce the content of nitrogen oxides (NOx) in exhaust gases generated 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 the combustion process and thus reduce the combustion temperature. The EGR system operates only at certain temperatures, barometric pressure and engine load to prevent deterioration of 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 the combustion process.
- Vacuum pump - The vacuum for the vacuum actuator of the EGR valve is generated by a camshaft-driven mechanical pump called a vacuum pump. The vacuum pump runs continuously when the engine is running.
- EGR Valve Vacuum Actuator Control Solenoid - The EGR 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 signal (PWM) through the ground circuit of the solenoid valve for controlling the vacuum actuator of the EGR valve, in order to open the EGR valve to the desired position using a metered supply of vacuum from the vacuum pump. The EGR vacuum actuator control solenoid is supplied with ignition voltage through the ignition 1 voltage circuit from the main relay. The EGR vacuum control solenoid valve is of a normally closed type.
- EGR throttle actuator control - Diesel engines do not create enough vacuum to allow the recirculated exhaust gases to enter the combustion process on their own. When the EGR throttle is closed, it prevents fresh air from entering the engine, causing it to create a vacuum. When the ECM is commanded to open the EGR valve, the EGR throttle is commanded to close. The EGR throttle valve is of the normally open type.
- MAF sensor -MAF sensor (mass air flow) located in the air intake system between the air filter and the EGR valve outlet port. The ECM uses the signal from the mass air flow sensor (MAF) to calculate the actual flow rate 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 supplying compressed air to the combustion chambers, which burns more fuel with an optimal fuel-air mixture. In a conventional turbocharger, the turbine is rotated by the action of exhaust gases from the engine on the turbine blades. This rotates the compressor wheel at the opposite end of the turbine shaft, pumping more air into the intake system.
On this vehicle's turbocharger, the position of the turbine blades is controlled by the engine management controller (ECM), whereby the turbocharging pressure is regulated. In this way, the boost pressure can be adjusted independently of the engine speed. The blades are fixed on a common ring, which can be rotated to change the angle of the blades. The ECM changes boost based on engine load.
Description of Diesel Particulate Filter System (DPF)
The exhaust gas treatment system of a diesel engine consists of a starting catalyst located in the engine compartment (precat) and a catalytic converter located under the body (main diesel oxidation catalyst + coated diesel particulate filter).
Engine management and exhaust gas treatment systems are designed to reduce the content of harmful substances such as hydrocarbons in exhaust gases (HC) and carbon monoxide (CO), as well as solid particles (soot) in order to comply with today's stringent exhaust emission 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 engine exhaust gases to reduce soot emissions into the atmosphere. Soot particles accumulate in the channels of the coated diesel filter and are burned at regular intervals (in a process called "regeneration"), to prevent clogging of the filter. Excessive accumulation of soot in the filter can lead to a drop in engine power and filter failure during regeneration. To increase the temperature of the exhaust gases during regeneration, additional fuel is injected into the filter through a plurality of injectors. During this time, the temperature in the DPF rises to approximately 600°C and the accumulated soot oxidizes or burns off into carbon dioxide (CO 2).
The pressure tubes connected to the differential pressure sensor measure the level of soot deposits in the coated diesel particulate filter and protect the engine by initiating a regeneration process when a critical soot level is reached.
Starting catalyst in the engine compartment (precat) and main diesel catalytic converter (DOC) coated with a noble metal and serve to reduce the content of hydrocarbons in the exhaust gases (HC) and carbon monoxide (CO). In addition, during regeneration, these units contribute to an increase in the temperature of the exhaust gases by burning the additionally injected fuel. Additional injection of fuel into the cylinders allows regeneration under any engine operating conditions, as well as at any values of outside temperature and pressure. The regeneration process proceeds smoothly and is usually imperceptible to the driver of the vehicle.