A Passat 2 car, equipped with 01N automatic transmission, accumulatively runs 37 thousand and 500 km, there is no reverse gear failure. After the crash, the first test is carried out, and it is found that, as the customer describes, it can run normally at the D position, but the R gear is hung, and the engine speed should be raised to slow down. According to the condition of the test, and consulting the maintenance manual, it is considered that there are no fault points for the reverse gear: valve assembly failure, solenoid valve malfunction, reverse gear clutch K2 skidding, sub shift valve damage or improper adjustment; 1/ reverse gear brake B1 skid; 1/ reverse gear brake seal plug leakage; related line fault; automatic transmission control unit fault. Wait. Read the fault code of the automatic transmission system with the fault detector and show that the system is normal. Pull down the automatic transmission of the solenoid valve traverse connector, let the automatic transmission enter the emergency state, in this state, only 1 gear J gear and R gear can be used, at this time the automatic transmission in the D position is 3 gear, at 1 is 1 gear, at the R position is R gear. But the test found that there was no R gear, indicating that the failure was not in the automatic transmission electronic control system, automatic transmission without R gear should be caused by mechanical failure. Put the transmission rod into the D bit for the stall test, the stall speed is normal (the correct value of the engine stall speed is 2400 r/min -2600 r/min, if the speed exceeds 2600 r/min, it shows that there is part skidding in the automatic transmission); the stall test is done at the R bit, the stall speed is over 35001 plus NN, too high; the stall test is done when the L gear is moved. Test, the speed of stall is normal. The stall test shows that the parts of R block are slipping. From the executive element worksheet of each gear, it is known that the reverse gear clutch K2 and 1/ reverse shift brake B1 work in the R gear, the clutch K1 and the reverse shift brake B1 work in the manual l gear, the clutch K1 and the one-way clutch F work in the D bit 1 gear. From the analysis of the working parts of the gears, the fault should be caused by the K2 slip of the reverse clutch. So decided to disassemble the automatic transmission, and check the reverse gear K2 and its oil well. When the automatic transmission is disintegrated, the friction material is found in the automatic transmission oil (ATF). When the automatic transmission is removed, it is found that the friction material of the brake B2 has a friction piece. The friction plates of clutch KI, K2 and K3 were removed and no problems were found. No abnormalities were found in the working conditions of the clutch Kl, K2, K3 and brake B2 from compressed air. Remove the valve body, remove the L/ reverse brake B1 seal plug, and check the working condition of the brake B1 with compressed air. No abnormalities are found. The brake B1 friction disc was removed and no problems were found. At this point, it is considered that the fault should be caused by the valve assembly or manual shift valve damage or improper adjustment, because there are friction material fragments in the ATF, the body assembly should be replaced according to the requirements of the maintenance manual, so the friction plate and body assembly of the B2 brake are replaced, and the manual shift valve should be adjusted strictly according to the requirements in assembly. . After automatic transmission test, failure still can not be ruled out. Is the diagnosis wrong? Because the valve assembly is replaced, and the manual shift valve is adjusted strictly in assembly. The most possible reason is the sliding clutch K2 skid and the 1/ reverse gear brake BI skidding. Then dismantling the automatic transmission and re - disintegration check found that the piston of the 1 reverse gear brake Bl is damaged (not carefully observed), the piston is not sealed, resulting in the J/ reverse gear brake BI skidding. Replace the piston of the 1/ reverse brake BI and reassemble the automatic transmission test run. Why did the first disintegration automatic transmission check not find the fault point? It is considered to be a mistake in the maintenance manual of the vehicle and the work table of each of the block executive components introduced by the training data. In the R gear, the actuator has the reverse clutch K2 and the brake B1; in the manual 1 gear, the actuator has the clutch K1 and the brake Bl; in the D bit, the actuator has the clutch Kl and the one-way clutch F. Therefore, the miscarriage of justice was not caused by the slip of the clutch K2, and the inspection of the brake BJ was ignored during the disassembly inspection. The actuating element work table of each block should be the clutch K2 and the brake BJ in the R gear. In the manual l gear, the actuator has the clutch K1 and the brake B1 if B1 skids, then the one-way clutch F takes part in the work, and the 1 gear can work, but at this time there is no mechanism action. This is the key to the diagnosis of the fault. Because of the error in understanding the working table of each block, the engine has no braking effect when the manual L is not tested in the road test, so it is misjudged. This led to the failure of automatic transmission checking for the first time. Check the working condition of clutch K1, K2, K3, and brake Bl and B2 with compressed air. It can only check whether the piston moves, whether the piston has serious leakage or whether the piston has slight leakage is not accurately judged, which should be paid special attention to during the maintenance.