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The Dongfeng, which runs about 33 thousand km, produces the Li Wei. Customer response: the engine fault lights of the car are bright, the exhaust has peculiar smell, smoke black, the engine speed is unstable, and there is a jitter phenomenon. After asking the customer to know the car's newly bought used car for the customer, after buying back for a period of mileage, the car was carefully checked for the accident car and the record not maintained at the 4S store. Fault diagnosis: after the confirmation of the fault, at first, the engine fault lights up, step down the accelerator pedal, the engine speed can only be added to 2500 rotation, it is judged that two kinds of conditions will cause such fault, first, air flow sensor damage; second, sensor circuit open circuit short circuit. Fault detection uses CONSULT-3 to read out the engine fault code as DTCP0113, intake temperature sensor and P0102 mass air flow sensor. Check the ESM Liwei maintenance manual. The possible reasons are: MAF sensor wiring harness open or short circuit, air leakage, MAF sensor damage. 1) strictly follow the instructions of the maintenance manual to check that the intake system is not abnormal. 2) check the circuit diagram, check the MAF power supply, the signal line and the intake temperature sensor wire harness are normal; 3) when checking the MAF sensor wire harness, it is found that the sensor plug is damaged, it is suspected that the plug and sensor contact caused by the plug breakage are bad, the MAF plug is repaired after the fault code is removed and the barrier does not exist; 4) due to the intake temperature sensor With MAF sensor as a whole, the fault may be a problem. When the engine is restarted, the fault light is lighted again. Read fault code DTC or P0113 or P0102 with CONSULT-3. As the wiring harness is switched on, the replacement of the new MAF sensor is still in trouble. 5) this car is an accident car, and check the engine computer needle normal, there is no damage to the phenomenon, found that the plug has too many stains, cleaning the plug in the stains, after connecting the ECV plug, clear fault code, the failure disappeared. Maintenance summary: the cause of this car failure is that in the repair of the car, because the maintenance is not careful, in the assembly process, there is no careful cleaning of the stains and dirt in the plug, causing the MAF sensor to enter the failure protection mode and cause the engine fault light to light.