In order for numerous electronic control units to exchange data with each other, these units are connected by a high-speed CAN data bus (see Chapter 5). The CAN bus consists of two lines, which allows to reduce the amount of electrical wiring. Each control unit can simultaneously transmit and receive data, but each specific unit reads from the CAN bus only the data it needs.
The principles of organizing fuel and air supply systems are described in Section 1.
A description of the sensors and components used by the engine management system to reduce exhaust gas toxicity is provided in Parts B.
The information from the sensors listed below and some others is used by the ECM to generate control voltages that are sent to the actuators to ensure optimal engine operation in any situation. If some sensors fail, the control unit switches to the emergency program mode to prevent possible engine damage and ensure further vehicle movement.
The Engine Control Module (ECM) determines the optimal ignition timing (on petrol models) and injection, as well as the amount of fuel injected, is coordinated with other vehicle systems. On gasoline models, the high voltage for spark generation is generated by the ignition module on the signal from the ECM.
The crankshaft position sensor (CPS) provides the engine control unit with information about the crankshaft speed and its exact position. This information is used to determine the injection timing. The CPS sensor is located on the rear of the engine and works on the basis of the Hall effect, scanning the teeth of the rotor mounted on the crankshaft. One of the teeth is missing, and detection of this gap indicates that the crankshaft is in the position corresponding to the TDC position of the compression stroke of the piston of cylinder No.1. If the CPS sensor is faulty, the engine shuts down and will not start.
The camshaft position (CMP) sensor works similarly to the CKP sensor by scanning the toothed rotor at the end of the camshaft. The CMP sensor, together with the CKP sensor, is used to determine the TDC of the piston of the first cylinder and to determine the injection sequence.
Knock sensor (KS only on petrol models) screwed into the cylinder block, prevents the occurrence of shock combustion of fuel. Thanks to this, the ignition timing is maintained at the detonation limit, which ensures better use of fuel energy and, thus, a reduction in fuel consumption. In the absence of a signal or when the signal from the KS sensor disappears, knock control is switched off and the ECM switches to an operating mode based on basic values, far from the actual values of the detonation limit. In this case, detonation combustion can lead to engine damage.
Engine coolant temperature information from the ECT sensor is used by the ECM to calculate fuel injection timing and duration, which vary depending on engine temperature.
The gas pedal module consists of a gas pedal, a support bracket, springs, a rotary trunnion with two magnets and a dual gas pedal position sensor (APP). In the gas pedal module with "Kickdown" function (on models with DSG) an additional compression spring with a stop is installed between the gas pedal and the support bracket so that the driver feels the moment the "Kickdown" function is activated. The operating principle of the APP sensor is contactless, based on the Hall sensor. The ECM uses the signal from the APP sensor to calculate the amount of fuel injected. If the APP sensor fails, the engine idles at an increased speed and does not respond to pressing the gas pedal.
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Clutch pedal position sensors (on models with manual transmission) and brakes monitor the position of the corresponding pedals to ensure cruise control and transmission operation. The transmission neutral position sensor is used to authorize engine starting on DSG models.
The engine oil level and temperature sensor is designed for a more flexible oil change interval. The sensor information is used to determine the oil level and quality. When determining the oil quality, the deposition of soot particles in the oil is also taken into account. The soot deposit parameter is determined empirically and saved in the corresponding characteristic.