【Fault description】
    Equipped with A340 automatic transmission, the car in the process of driving the instrument panel O / DOFF indicator light, the impact of a larger shift.
    【Inspection process】
    (1) first check the automatic transmission within the hydraulic fluid, hydraulic oil normal and good oil quality, check and adjust the throttle cable.
    (2) Turn the ignition switch to the ON position, press the O / D main switch on the shift lever, and the O / DOFF indicator on the instrument panel is not clear. Check the connector in the connector with the TE1 and E1 terminals, then check the warning lights on the dashboard to display the normal code, and O / DOFF indicator light is on, no flash, no output fault code. Indicating that the engine control system is working properly, no fault, but also shows that the automatic transmission control system circuit or ECU automatic transmission control circuit is faulty.
    (3) the ignition switch to the ON position, first shift lever on the P file position, start the engine, the engine can start; turn off the shift lever on the N position, start the engine, the engine can start; Rods are placed in the R, D, 2, L file position when the engine can not start, indicating automatic transmission neutral start switch work properly. Press the O / DOFF main switch on the shift lever. The O / DOFF indicator on the instrument panel is always on by the O / DOFF main switch and indicates that the O / DOFF indicator is faulty. Press the PWR green indicator on the instrument panel when the switch is selected for the switch on the shift lever. When the switch is off, the PWR green indicator is off, indicating that the automatic transmission mode indicates that the circuit is normal.
    (4) in the completion of the above three inspection work after the road test, the car in the process, especially in the rapid acceleration, deceleration process, the transmission shift slow, the impact is more serious, gear shift is not smooth, and the dashboard The check warning light sometimes flashes several times and then goes off again; the O / DOFF indicator is on. Through the test, found that the fault does exist.
    (5) a comprehensive inspection of the automatic transmission control circuit and the main control components, remove the coolant temperature sensor from the engine, check the coolant temperature sensor in a variety of temperature resistance changes, check the results of coolant temperature sensor is normal, check finished And then replace the coolant temperature sensor.
    Release the automatic transmission of hydraulic oil, remove the oil pan and found no oil inside the shell of any impurities, the transmission is very clean, oil pump suction filter is also very clean, no clogging. Remove the No. 1 solenoid valve, No. 2 solenoid valve and lock solenoid valve harness connector, with a digital multimeter to check the resistance of the solenoid valve is about 13Ω (normal value of 11-15Ω); resistance value is normal; directly with 12V power supply electromagnetic Valve, the solenoid valve activity is normal, no clogging and jamming phenomenon, the solenoid valve is working properly. Check the wiring harness plug plug in the solenoid valve, install the oil pan and add the automatic transmission oil to the upper level of the dipstick.
    【Fault Analysis】
    Remove the combination instrument from the instrument panel, remove the ENG / AT control ECU from the back of the debris box on the right side of the instrument panel, remove the neutral start switch and the harness connector of the No. 2 speed sensor from the transmission; The meter checks the automatic transmission control line. After a thorough inspection, the measurement found that the following line faults were present in these control wires:
    (1) from the engine control ECU harness connector THW terminal to the coolant temperature sensor harness connector on the wire between the THW terminals due to damage caused by the insulation layer of wire short-circuit (ground) phenomenon, so that coolant temperature signal transmission disorder.
    (2) from the neutral start switch harness connector on the S2 terminal to the ECU wiring harness connector on the corresponding S2 terminal wire due to wire insulation layer damage to the wire instantaneous short-circuit fault, resulting in automatic transmission No. 2 solenoid valve does not work The
    (3) from the No. 2 speed sensor harness connector on the SP2 terminal to control the ECU wiring harness connector on the corresponding terminal between the wires due to wire insulation damage to the wire instantaneous short circuit (ground) failure, so that No. 2 speed sensor to the ECU The transmission speed signal is not normal.
    (4) shorting the wire between the O / DOFF indicator on the instrument cluster to the OD2 terminal on the control ECU harness connector and the shorting (ground) of the O / DOFF indicator to the ground, causing the O / D main switch Can not control the O / DOFF indicator, and control the OD2 terminal on the ECU can not receive the switch signal of the O / D main switch.
    【Maintenance】
    For the above check out the line fault, with a universal meter to find out the line of broken wire and short circuit of the specific location, the wire connected, bandaged and then check the meter once again, to confirm the wire after a good connection with insulating tape Wrap the harness and secure it securely. Plug in the ECU and all the control elements of the harness connector, fixed ECU and installed all the accessories and decorative parts after the O / DOFF switch test: press the shift lever on the O / DOFF main switch on the instrument panel O / DOFF The O / D switch signal circuit is turned off; O / D switch signal circuit is turned off when the O / D switch is released, indicating that the O / DOFF indicator line has returned to normal.
    【Maintenance】
    After the completion of the clearance of the fault code to carry out road test, after 100km continuous driving test, the car in the process of automatic transmission gear shift is very smooth, without any impact, the car is running smoothly, the car in the rapid acceleration and deceleration, the transmission response , Automatic transmission control system failure was completely ruled out. After the end of the test and then use the fault self-diagnosis system to retrieve the fault code, the results of the dashboard on the Check and O / DOFF indicators show the normal code, indicating that the automatic transmission control system is working properly, no fault.