Recently, the customer reflected the engine fault light. When the vehicle entered the factory, it was found that the engine fault light was always bright. The fault code is read by the diagnostic instrument as "P0741, torque converter clutch electromagnetic coil performance failure". Suspected fault parts: (1) electromagnetic coil line fault of torque converter clutch; (2) gear shift solenoid valve (DSL) fault; (3) valve failure; (4) hydraulic torque converter locking clutch failure. Fault diagnosis: record the fault code, check the stop frame data and find that the speed is between 70-80km/h when the fault occurs. After the fault code is cleared, the long time road test is carried out according to the condition of the failure, and the fault does not appear again. Doubt may be accidental trouble, let the customer run for a while and have a look. But customers go back to the store two weeks later to see that the fault light is on again. It is still P0741 to read the fault code with a diagnostic instrument. The wiring harness of the electromagnetic coil circuit of the torque converter clutch is tested according to the maintenance manual and the circuit diagram. Measure DSL (C61) 3 pin and body grounding 12S2, normal. The dam J volume ECM (C24) 7 needle and body grounding is also normal. Check that the wiring harness between the DSL (C6) connector and the ECM (C24) connector is not damaged. Stall test, stall speed of 2375r/min, also in the normal range. Remove the automatic transmission oil pan. Direct measurement of DSL (shift solenoid valve) has a resistance value of 12.34 ohms, within normal limits. Using batteries to directly supply power to DSL (shift solenoid valve), you can clearly hear the sound of "clatter" solenoid valves. This indicates that the solenoid valve is normal. It is the failure of the valve body or hydraulic torque converter, in line with the principle of easy to be difficult to post, replace the valve body of the fault vehicle into a normal vehicle body for trial. Because the failure can not be reproduced immediately, let the customer go back and try again. The customer did not go back long enough to call the trouble light again. After the customer went to the store, the fault code was read again. The fault code was found to be "P2770, the electromagnetic coil potential of the torque converter clutch is high", and the fault code is not the same fault code as the previous fault code, as shown in Figure 3. Through the analysis of the maintenance manual, the current situation of the trouble code is not brighter with the customer's failure light, and the trouble is eliminated. The conditions for the previous fault codes are different, and the DSL (shift electromagnetic valve) is also replaced. So I wonder if it was damaged in the last survey. Check the C61 connector without damage, check ECM's C24 connector to find a case of damage to one of the pins, check the maintenance data and find that the damaged pin is the No. 79 pin connecting the DSL (shift solenoid valve). After the damaged pin is repaired, the trouble code path test is cleared, and the fault does not appear again. Two weeks later, call the customer, and the customer can not see the trouble light again.