A customer response: a TOYOTA Camry engine fault light has come to the shop many times. After clearing the trouble code, it opened for a while. The fault light was lit again. There is no other unusual condition for the car to open. The technician checks the vehicle according to the customer's description. When the engine fault lights are on, there is no obvious abnormal condition when idle speed, acceleration and driving. Technicians use the IT2 intelligent diagnostic instrument to read the fault code as follows: P0031, oxygen (A/F) sensor, heater control circuit low (1 column 1 sensor). According to the maintenance manual analysis of the causes of failure: A/F sensor heater circuit circuit breakage; A/F sensor heater (1 sensor) fault; engine frequent /B (EFI relay) fault; ECM failure. Fault diagnosis: the technician first connects the IT2 into the Powertrain (drive system) /Engine andECT (engine and ECT) /DTC, and reads the fault code to P0031 (the A/F sensor heater control circuit is low), and reads the DTC's set data to find no other exceptions. According to the repair manual, the technician disconnects the C15A/F sensor connector and measures the C15-1 and C15-2 terminals (the A/F sensor heater + B and HT terminals) for 2.6 Omega, in the normal range (normal value 1.8 to 3.4 omega); the measurement of the resistance between C15-1 (HT) and C15-4 (AF-) terminals is infinitely large and normal, so A/F can be excluded. There is a fault in the sensor. The ignition switch ON position, measuring the voltage between C15-2 (+B) terminal and the body is 12.7V, normal. The power circuit of A/F sensor is preliminarily excluded. The resistance between C15-1 (HT) and C24-109 (HAlA) terminal of ECM is measured at 0.24 Omega according to the system circuit diagram. The barrier between the terminal and the body of the body is infinitely large, indicating that the circuit between the A/F sensor and the ECM is normal. The technician considered that the fault could be caused by an intermittent failure, so the fault code C was cleared and the vehicle was tested again, and the fault light was lit again when the vehicle passed a relatively bumpy road. It is still P0031 failure to re read the fault code through IT2 after returning to store. The technician enters the Utility (tool) /CheckMode (check mode) through the IT2 intelligent diagnostic instrument, thus switching the ECM from the normal mode to the check mode, and then sloshing the related parts with the hand. When the engine room J/B is vibrated, the fault light is lighted again, and the fault lights are tested repeatedly. This can be judged as the J/B related fault. When the J/B is removed and pulled out of the 1E plug, it is found that the plug terminal has an obvious corrosion. In the combination of the circuit diagram, it is found that terminal 1E-7 is the power line of the A/F sensor heater; after the corrosion is processed, the fault is ruled out repeatedly.