A Mercedes Benz 600SEL limousine with a mileage of over 286 thousand km. User response: the vehicle appears to be slow and slow in acceleration, especially when it is accelerating. After replacing the electric fuel pump, the gasoline filter, the air filter, the distributor cap, the fire head, the spark plug, the temperature sensor of the coolant, and the cleaning of the injector and the oil tank, the failure is still the same. Troubleshooting: (1) analysis of the cause of the failure according to the failure phenomenon, this is the engine acceleration malfunction, the possible cause of the ignition system or fuel supply system parts failure, the intake system is blocked or leak, engine electronic control system failure. Because the relevant parts have been replaced and cleaned, the biggest possibility of the fault lies in the electronic control system of the engine. (2) the troubleshooting method is the first routine inspection of some items related to the failure phenomenon: check the pressure of each cylinder, the running situation of idle speed, the ignition of each cylinder, the good fuel injection of the injector and so on. All the results have not been found out, and the working conditions of each cylinder are also the same. Normal. Then check the components of the electronic control system that have an impact on the engine's acceleration performance: check the air flow sensor and the oxygen sensor are normal; the variable timing solenoid valve, the exhaust gas recirculation solenoid valve, the carbon tank solenoid valve are also normal. Considering the complex electronic control system of the car, and equipped with electronic acceleration / speed / idle speed control system, and the control system failure also shows a bad acceleration failure phenomenon, so the system is checked emphatically: after starting the engine, the acceleration pedal and the spring energy of the electronic throttle motor are gradually stepped down. The action of the accelerator pedal gradually follows the same frequency, indicating that the electronic throttle system works normally. At this point, the remaining faults may be the electronic controller and the corresponding circuit of the fuel injection system and ignition control system. If there is a failure of the fuel injection and ignition electronic controller and the corresponding circuit, the engine failure inspection indicator on the dashboard should be lighted, but the light work is normal. In view of the need for thorough inspection, a special fault diagnostic instrument is used to read the fault code. The fuel injection control system has no fault code, the electronic ignition control system has the fault code, the fault is "the right column cylinder ignition timing delay too much" and "the right column cylinder deflagration control is bad". For the sake of prudence, after debugging the trouble code, try the car again, and read the fault code again, the result is the same fault code. According to the fault information provided by the two fault codes, the possible faults are as follows: the right column deflagration sensor has a problem, the right column ignition electronic controller (ECU) has a fault, the right column cylinder is loose and the vibration is produced. The signal produced by the deflagration makes the ignition control ECU mistaken for the deflagration of the generator, and the ignition advance angle is pushed by mistake. It's late. According to the hint of the fault code, all the cylinders, parts and bolts of the right column are checked first, and the two deflagration sensors are checked, after the ignition switch is connected, the cylinder block near the detonation sensor is knocked out, and the signal is output, indicating that the deflagration sensor is good; the only fault possibility is left to the right column ignition electronic control. The system is ECU. Since the price of ECU is higher and the engine fault indicator is working normally, it is necessary to check again to find out faults beyond ECU. Dismantle the dashboard and continue to check that the engine fault indicator is connected by a wire to the generator charging indicator control circuit, so that the engine fault indicator lights up and out as the charging indicator, thus losing the function of the fault warning. This may be the real reason that the engine failed to find fault in the past because of the engine fault indicator light, and the troubleshooting personnel mistook the light. At this point, the real cause of the fault can be confirmed, that is, the right ignition control system ECU is damaged. (3) troubleshooting measures to replace the right ignition control system ECU, the engine accelerated smoothly, stepping on the accelerator pedal, the engine speed increased quickly, troubleshooting. Fault analysis: the model has two fuel control system ECU and about two ignition control system ECU, which control the injection and ignition of the right column (1~6 cylinder) and the left column cylinder (7~12 cylinder) respectively. It is precisely because of the ECU fault of the right ignition control system that the ignition time of the right column cylinder can not be properly controlled, and the ignition advance angle can not be adjusted correctly with the change of the engine condition, thus causing the engine to accelerate the bad acceleration. Because of the failure to find the true cause of the fault in the previous maintenance, the engine fault indicator light lost the fault warning function of the engine fault indicator, which is conveniently and wrongly changed to the engine fault indicator light line. Although the "normal work" of the engine fault indicator has been misleading for the failure inspection of the engine, the fault code reading operation should be carried out first, regardless of the light of the engine fault indicator when the electronic control system is overhauled. This is because when some electronic control system parts or circuits fail, the engine fault indicator does not light up the warning; when the ECU itself has a fault or the engine fault indicator circuit has a fault, it will not be warning when there is a failure. If this fault can achieve "fault code priority", it may save some troubleshooting operations and eliminate faults more quickly.