Solenoid valve failure will have a direct impact on the switching valve and regulating valve action, the common fault solenoid valve does not act, should be checked from the following aspects: (1) Solenoid valve loose or thread head off, the solenoid valve can not be tight, tight Thread fixed head. (2) Solenoid coil burned out, remove the solenoid valve wiring, with a multimeter to measure, if the open circuit, the solenoid valve coil burned out. The reason is the coil damp, resulting in poor insulation and leakage flux, causing the coil current is too large and burned, so to prevent rain into the solenoid valve. In addition, the spring is too strong, the reaction force is too large, the number of coil turns is too small, and the suction is insufficient, the coil can also be burned. In emergency, the manual button on the coil can be turned to "1" position by the "0" bit during normal operation, so that the valve is opened. (3) solenoid valve stuck. Solenoid valve sleeve and valve spool with a very small gap (less than 0.008mm), are generally a single assembly, when mechanical impurities into or too little oil, it is easy to get stuck. Approach can be used steel wire from the hole into the head, make it bounce. The fundamental solution is to remove the solenoid valve, remove the valve plug and spool sleeve, with CCI4 cleaning, making the spool movement in the valve sleeve flexibility. Disassembly should pay attention to the assembly sequence and the location of external wiring in order to reassemble and wiring properly, but also check the oil mist hole is blocked, the lubricating oil is sufficient. (4) leaks. Leakage will result in insufficient air pressure, making it difficult to open and close the forced valve due to damaged gaskets or slide valve wear caused by several cavity blow-by gas. In dealing with switching system solenoid valve failure, should choose the appropriate time, and so on when the solenoid valve is in power loss processing, if not within a switching gap processing, the switching system can be suspended, calmly deal with.