What's the Automotive Diagnostics

Without disintegration (or remove the individual parts only) conditions to determine technical condition of vehicle, check the fault location and identification of the cause. Including the detection and diagnosis, chassis detection and diagnosis, detection and diagnosis Auto Body and accessories, as well as vehicle exhaust and noise detection, etc. of an automobile engine.
Hyundai Motor fault diagnosis technology electronically controlled fuel injection car engine control computer ECU, set up a self-diagnostic system, which is mainly used to monitor the working status of each member of the electronic control system, and depending on the configuration of the electronic control system, to confirm the diagnosis how much the number of failures. When EFI Automotive self-diagnostic system detected a fault, on the one hand it enable protection fault, the control system necessary protection; on the other hand, it is a fault in the fault code stored in random access memory (RAM) , and the fault indicator lit simultaneously (CHECK ENGING). Vehicle maintenance personnel in accordance with certain procedures, failure to read the fault code, and then check through the relevant technical data, fault code shown understanding carefully, automotive electronic control system can carry out the purpose of fault repair.
Diagnosis Method Editor
Self-diagnosis
Automotive normal operation, the electronic control unit (ECU) of the input, the voltage value of the output signal has a certain range. When the voltage value of the signal exceeds a certain range, and this phenomenon will not disappear over a period of time, the ECU determines whether or failure of this part. ECU put this fault code is stored in the form of internal random access memory (RAM), while lights troubleshooting lights (such as CHECK ENGINE, SRS, ABS, etc. LED), which is the basic principle of self-diagnosis. When a circuit generates a fault, the signal can not be used as a control parameter of the engine to use.
In order to maintain operation of the engine, ECU begins its program memory (ROM), and call up a fixed value for the engine emergency parameters, ensure that the engine can continue to operate. When the ECU computer system fails, the backup control circuit ECU automatically enables simple control of the engine, making the car can start to go home or to a nearby garage for repairs, this function is trouble-free operation, also known as "claudication "mode. On the other hand, when a faulty actuator ECU detects, for safety reasons, to take some security measures. This function is called failsafe.
ECU fault diagnosis system for sensors, actuators, and computer systems carried out. When the sensor and computer malfunction, often taking trouble-free operation mode. When the actuator failure often take failsafe measures.
sensor
Since the sensor itself generates an electrical signal, and thus, troubleshooting the sensor does not require dedicated lines, but only in software, preparation of sensor input signal recognition program can be realized on the sensor fault diagnosis. Normal input voltage value of the water temperature sensor 0.3-4.7V, corresponding to the engine cooling water temperature is -30-120 ℃. So, when the ECU detects the voltage signal out of this range the amount, if it is once in a while, diagnostics ECU is not a malfunction. However, if the signal is not normal for a period of time, i.e., the diagnostic program determined that the cooling water temperature sensor or circuit malfunction. ECU In this case the code (this code is designed to have a good agreement on behalf of the water temperature sensor fault signal abnormal digital code) is stored in the form of random access memory. Meanwhile, the check engine warning light "CHECK ENGINE", inform the driver and maintenance personnel, the engine control system malfunction. When ECU found the water temperature sensor is not functioning properly, it uses a pre-set constant temperature signal value as an alternative, to make the system work in the running.
Computer System
Microcomputer system if a failure occurs, the control program can not be normal operation, the microcomputer is in an abnormal state. And this will make the car due to engine control system failure can not travel. In order to ensure the car could continue running when the computer fails, control systems engineering, design reserve circuit (IC backup system). When the ECU computer malfunction, ECU automatically call the reserve circuit complete control tasks into simple control operation, with a fixed control signal, the vehicle continued to travel. Since the system only has a simple function to maintain the engine is running and the computer can not replace all the work, so this backup job to go back to the road, also known as "limp" mode. When using backup systems work, fault indicator light. Whether the computer is working properly carried out by the monitoring circuit is called a circuit monitor. Monitoring circuit is installed independent of the computer system of the counter. Microcomputer normal operation, run by the microcomputer program counter clearing processing timing. Thus, monitoring the value of the counter circuit is never an overflow phenomenon. When the computer system is not running phenomenon occurs, the microprocessor can not counter this timing is cleared, so that this monitoring counter overflow occurs. Monitor counter overflow output level from low to high (This output typically carry flag counter. When the counter reaches its maximum value, and then add a count pulse, the counter will overflow occurs. In this case, the counter overflow level by the end of the low to high; at the same time, the counter is cleared). This change counter output level will directly trigger the alternate circuit. Spare circuit only in accordance with the start signal and the idle contact closed state, a constant injection duration of the fuel injection and ignition timing and ignition control.
Actuator
Automotive electronic control systems, the actuator is to determine the operation of the engine and the main cars with safety device, when the actuator fails, often driving the car will have been affected. Therefore, treatment is usually actuator failures: When the actuator is recognized as failure by the ECU to take appropriate security measures implemented in accordance with the severity of the failure in the control system, and designed a fail-safe system.
Since the ECU of the actuators is to control operation, the control signal is the output signal. Therefore, in order for the work of each actuator diagnosis, generally adding circuit fault diagnosis, namely ECU issues a control signal, the actuator must be a dedicated circuit to feedback on its implementation to the ECU to the actuator. Electronic engine control system, a typical member of the actuator fault diagnosis is ignition. Under normal circumstances, when the ECU to control ignition, ignition once for each ignition, the igniter will be confirmed by the ignition circuit within the ignition performance in the form of an electrical signal back to the ECU. When the ignition circuit or faulty ignition, ignition control ECU command is issued, get feedback signal; at this time that the ignition has been ECU will not work properly. Engine operation, if the ignition system failure, will make the unburned gas mixture into the exhaust system and the exhaust pipes. The exhaust gas purification device in the catalyst temperature will greatly exceed the allowable value. Meanwhile, the unburned gas mixture in the exhaust pipe gathering too much can also cause explosion of the exhaust system. For this reason, the use of fail-safe system, when the ECU does not receive an acknowledgment signal fire, immediately cut off the fuel injection system the power to stop the fuel injection.

some famous car diagnostics brand such as LAUNCH X431 5C Autel Maxidas DS708
Skp900 Key Program   VXDIAG VCX