A 2006 mile Shanghai Santana 2000 car with a mileage of about 90 thousand km and equipped with BSA engine. User response: the engine failed to start the engine. The inspection and analysis showed that the car was pulled over and repaired by the rescue vehicle because the engine was unable to start. At that time, a preliminary inspection was carried out, and the ignition system was not ignited. It was thought to be an ignition module fault. But after replacing it, the engine was still unable to start the engine and then replaced the spark plug, high pressure line, and crankshaft. Position sensor and so on, but there is still no effect. Verify the fault after the car is connected. Starting the engine, it is found that there are occasional signs of engine trouble. According to the analysis of the phenomenon, there should be no high pressure fire. Then let a person in the car in charge of starting the engine, I pulled out of the car out of the cylinder line "fire", found that the 1 cylinder line does not "jump fire", and then pull down the 2 cylinder line again "test fire", found that the fire is normal, is the 1 cylinder high pressure line has problems? Retry a group of sub - cylinder lines again, and the result is the same. Considering that the car uses the group control ignition method, it is suspected that the 1 cylinder and 4 cylinder do not ignite, while the 2 cylinder and 3 cylinder ignition are normal. After further verification, this is true, so that the scope of the fault will be reduced to just 1 cylinders and 4 cylinders without ignition. Since the ignition module and the cylinder line are all new, the fault location may be in the relevant lines and the engine ECU itself. Connect the fault detector to query without fault code storage. No obvious exception was found in reading engine related data streams. Then check the conductance of the ignition module connector terminal 1 to the 57 line of the engine control unit connector terminal, and normal, and the conductance of the ignition module connector terminal 3 to the engine control unit connector terminal 71 is also normal. Is there a problem with the engine control unit? In order to find the cause faster, then the ignition module on a normal vehicle was replaced by a theft proof matching test, and the fault remained. Rethink the idea again, according to the working principle, since the engine control unit itself is normal, the problem is still on the control line that controls the ignition of the 1,4 cylinder. Although the control line is normal, the fault will still be caused if the bypass is short circuited. Then a multimeter was used to measure the resistance between the terminal 1 of the ignition module connector and the resistance of the iron lap. At last the cause of the fault was found, and the direction of the control line was looked up, and the control line was found to be tied with the body. Troubleshooting: the ignition module control line for handling abnormal grounding.