Symptoms and Solutions for Transmission Solenoid Valve Failure
In a transmission, the mechatronic control unit (ECU) often has the highest failure rate, and its technical complexity and repair costs are relatively high. However, this article will narrow its focus and examine a key component between the valve body and the computer: the solenoid valve. Despite its compact size, it plays a crucial role in the entire transmission system.
How to Determine the Working Condition of a Solenoid Valve
To check whether a solenoid valve is functioning properly, you can use the following methods: First, supply the solenoid valve with the controlled medium-pressurized liquid or air-at a pressure within the solenoid valve's operating pressure range. Then, energize the solenoid valve's coil. If the controlled medium smoothly switches from open to closed or back again, the solenoid valve is in good condition. If it fails to do so, a fault may exist.
The Impact of Solenoid Valve Failure on Vehicles
The solenoid valve plays a critical role in a vehicle's transmission, controlling the oil pressure within the transmission and, in turn, affecting gear shifting. If a solenoid valve malfunctions, the vehicle will exhibit a variety of unusual symptoms, such as shifting jerks, slipping, shift shock, and inability to shift up.
How can we diagnose and troubleshoot solenoid valve failures? First, use a multimeter to measure the continuity of the solenoid valve coil. If the resistance is abnormal, the coil may be short-circuited or open-circuited. However, even normal resistance may not completely rule out a coil failure. Therefore, a final test is necessary: use a small screwdriver to approach the metal rod inserted into the solenoid valve coil. If magnetism is felt after power is applied, the coil is functioning properly; otherwise, it needs to be replaced.
The most direct solution to a solenoid valve coil failure is to replace it.
Common Fault 2: Solenoid Valve Plug/Socket Problems
If the solenoid valve uses a plug/socket design, problems such as problems with the socket's metal reed or incorrect plug wiring (for example, mistakenly connecting the power cord to the ground wire) may prevent power from reaching the coil properly. To avoid these problems, it is recommended to tighten the retaining screws after connecting the plug to the socket. Also, tighten the retaining nut after assembling the valve stem and coil.
Furthermore, if the solenoid valve coil's plug is equipped with an LED power indicator, ensure correct wiring when using a DC power supply; otherwise, the indicator will not illuminate. Also, be careful not to mix up power plugs with LED power indicators of different voltage levels to prevent the LED from burning out or shorting the power supply.
For solenoid valve coils without a power indicator, polarity does not need to be maintained. However, if the coil voltage is DC and a diode/resistor leakage circuit is connected in parallel, polarity requirements may apply.
For this type of fault, possible measures include correcting wiring errors and repairing or replacing components such as the plug and socket.
Common Fault 3: Solenoid Valve Spool Failure
Ensure the pressure of the medium passing through the solenoid valve is normal. Try pressing the red manual button. If the solenoid valve does not respond, meaning the pressure medium does not change, the valve core is considered damaged.
For this problem, first check whether there are any issues with the medium itself. For example, check if there's a large amount of water in the compressed air (note that oil-water separators are sometimes ineffective, especially if poor piping design results in excessive water accumulation before the compressed air enters the solenoid valve) or if there are excessive impurities in the liquid medium. Next, remove any water or impurities from the solenoid valve and its piping. If the problem persists, repairs (such as replacing the valve core or the entire solenoid valve) may be considered, but this requires the necessary time, patience, and necessary effort.
