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 only the data it needs from the CAN bus.
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.
Information from the sensors listed below and some others is used by the ECM to generate control voltages 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 movement of the vehicle.
The Engine Control Module (ECM) determines the optimal ignition timing (on petrol models) and injection, as well as the amount of injected fuel, is coordinated with other vehicle systems. On gasoline models, the high voltage for sparking is generated by the ignition module in response to a 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 injection timing. The CKP sensor is located on the rear side of the engine and operates on the Hall effect by scanning the teeth of the rotor mounted on the crankshaft. One of the teeth is missing, and the 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 CKP sensor is faulty, the engine will shut down and will not start.
The camshaft position (CMP) sensor works similarly to the CKP sensor by scanning the toothed rotor on the end of the camshaft. The CMP sensor, together with the SKR sensor, is used to determine the TDC of the piston of the first cylinder and determine the injection sequence.
Knock sensor (KS, only on petrol models) screwed into the cylinder block, prevents the occurrence of impact 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 its consumption. If there is no signal or if the signal from the KS sensor disappears, knock control is disabled and the ECM switches to the operating mode based on base values, which are far from the actual knock limit values. 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.
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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. When the APP sensor fails, the engine idles at high speed and does not respond to pressing the gas pedal. Clutch pedal position sensors (on models with manual transmission) and the brakes monitor the position of the corresponding pedals to ensure the operation of the cruise control and transmission. The transmission neutral position sensor is used to enable engine starting on DSG models.
The engine oil level and temperature sensor is designed for more flexible oil change intervals. Information from the sensor is used to determine the oil level and quality. When determining the quality of oil, the deposition of soot particles in the oil is also taken into account. The soot deposition parameter is determined empirically and stored in the corresponding characteristic.