Failure diagnosis of Buick car
  • Automotive

A Buick GS car is equipped with V6 and 2.98L engines, with a mileage of 120 thousand km. The vehicle can not start up, and all the instrument indicators are extinguished. According to the owner, the car accidentally broke the ignition key chip a week ago. It was only a poor acceleration, and there was no failure to start. 1. because the instrument indicator of the vehicle is completely extinguished, so there is a breakdown of the instrument indicator circuit, which may be caused by the circuit breakage of the instrument power line or the burning loss of the instrument. 2. the starting system circuit of the car is shown in Figure 1. There are many possible reasons for the failure of the engine to start. According to the actual situation of the vehicle, the following are analyzed. (1) the lever position of the transmission is wrong. It is not placed in the "P" position (parking) or "N" position (space position). Because of the failure of the instrument circuit, the position can not be displayed correctly or not. 2. The machine's own fault causes it to be unable to start. 3. Failure of the starting system leads to failure of the starter. (4) the fault of 3X signal causes the fuel control system to not work properly, resulting in failure to start. Failure of the ignition key resistor chip causes the starter to not start. Failure of the body computer can not identify the correctness of the key signal, causing the starter to not start. In view of the above analysis, the instrument line should be checked first, and then the starting line should be checked. 1. check the instrument line, the insurance burn, after changing a 10A instrument insurance, turn on the ignition switch, the instrument indicator light is lit. At this time, the engine fault indicator light MIL lamp on the right side of the dashboard and the safety indicator light SECURITY light on the left side of the dashboard light and flicker at the same time, indicating that the safety system of the engine and body is stored in trouble. 2. observe the transmission shift indicator on the dashboard and the shift lever is at "P". 3. place the ignition switch at the start position, and the starter does not show any signs of operation. There are no breakdowns in the starting line, the main connection column of the starting machine, the starting machine operation, but the engine can not start, indicating that the starting machine itself is no fault or is not simply starting line fault. Since the engine and safety indicator lights are lit, the fault code should first be extracted by diagnostic equipment. 4. the fault diagnosis interface is found at the lower left of the dashboard, using the Buick special detector Tech2 to read the fault code, and get the following power control system fault display: P0102 - air flow sensor fault; P0118 - coolant temperature sensor fault; P0122 - throttle position sensor fault; P1374-3X reference circuit fault. Using Tech2 to read the body control system failure code is as follows: the key code is invalid; 5. because the engine can not operate, the fault code can not be removed and the fault code can not be re extracted. Therefore, it is impossible to determine whether there is a historical fault code in these faults, so it can only be checked and eliminated one by one according to the fault code read out by the instrument. It was found that, except for the circuit breakdowns of the throttle position sensor, no other sensor failures were found, and the ignition key was unable to determine whether the chip resistance was correct or not because of no standard data. 6. reconnect the throttle position sensor line and detect the circuit to eliminate its circuit breakdowns. After careful examination and examination of the content described by the owner, it is determined that the failure to start is caused by the damage caused by the resistance of the ignition key chip, which leads to the error of the identification signal of the body computer, and thus the anti-theft function is started. The only feasible solution is to re find a set of matched resistance data from 15 sets of chip resistors and replace them with suitable resistors. 7. use special instruments to access the anti-theft circuit, start with the first group, and test them one by one. If the SECURITY indicator on the dashboard can be extinguished, the resistance value of the group is the resistance value of the ignition key chip. When tested to the fourteenth group, the safety indicator light on the dashboard is extinguished, and the resistance value is 9.7k ohm. 8. find a resistance of 9.7k Omega, connect the ignition key line Black / white line with the purple / white line, and scrape the residual chip resistor off the ignition key; open the ignition switch and the safety indicator on the dashboard to turn out after 2 to 3S; put the ignition switch on the starting position, the starting machine is running normally, but the engine is still not. Work. After careful inspection, it was found that there was no high-pressure spark and no fuel pump running. 9. calmly analysis the maintenance process, in the ignition "ON" instantaneous, the oil pump had 2S oil supply, indicating that the oil pump and its relay should be free of fault, check the oil pump line is normal, the fuel system should be no fault; no ignition signal is the only possible reason for the crankshaft position sensor 7X signal failure. The ignition system circuit of the car is shown in Figure 2. 10. check the crankshaft position sensor 7X signal, it is found that the 7X reference high signal provided by the sensor is not normally provided to the ignition control module ICM because the sensor plug is loose. Thus, ICM can not provide the converted 3X reference high signal to the power control module PCM, and PCM can not provide ignition and fuel supply letter. Number. 11. reconnect the line, use TECH2 to clear the fault code, start the engine, the instrument is normal, the engine is running normally. 12, the fault code is extracted again, and no fault code exists. 1. the vehicle is equipped with an ignition key with a resistive wafer, and a key detection circuit is formed through the inductive contacts of the lock core. When the ignition switch is transferred from the OFF bit to the ON bit, the body module BCM provides the reference voltage of the 5V to the detection circuit, which reads the resistance code and compares it with the pre set standard value. If the code is consistent, BCM sends a fuel - enabled password to PCM through the connection of the two level serial data and starts a burglar relay to control the action of the start - up relay and the fuel relay to make the engine start normally; when the code is inconsistent, the BCM stops the burglar relay through the PCM, the engine fuel supply stops and starts. The moving line is cut off. 2. in the control of the vehicle, the 7X signal of the crankshaft position sensor is very important. Once the open circuit fault occurs, the ignition and fuel supply system of the engine will stop working. Therefore, after removing the ignition key failure, the starter can operate normally, but the engine is still unable to start. The crankshaft position sensor 7X signal should be checked.