How to Determine if a Solenoid Valve is Good or Bad?
4 Answers
Methods to determine if a solenoid valve is good or bad: 1. Unplug the solenoid valve's connector. If the suction phenomenon stops, it indicates the solenoid valve is functioning normally. If suction continues, it means the solenoid valve is stuck in the open state. 2. Start the engine and let it idle. Remove the pipe connected to the fuel tank. You should feel a suction phenomenon at the carbon canister's connector, with a frequency of about two to three times per second. If there is no suction, it indicates the solenoid valve is stuck in the closed state. A solenoid valve is an electromagnetically controlled industrial device used as an automated basic component for controlling fluids, acting as an actuator, and is not limited to hydraulic or pneumatic systems. Solenoid valves are categorized into three main types based on their operating principles: direct-acting solenoid valves, step-by-step direct-acting solenoid valves, and pilot-operated solenoid valves.
Once at the repair shop, I saw a mechanic testing a solenoid valve like this: first unplug the connector, set the multimeter to the resistance measurement mode, and touch the probes to the two metal contacts of the solenoid valve. A normal solenoid coil should have a resistance between 20 to 60 ohms. If the reading shows infinite resistance, it means the coil is completely open. Then, connect a 12V battery to simulate power supply—a clicking sound indicates the valve core is functioning properly. If there's no response and it heats up, it's likely broken. For valve bodies with oil leaks, the seals need extra inspection. The shift solenoid valve on the transmission is most prone to sticking, so when experiencing gear shift hesitation, it should be checked first. If unsure, the most reliable method is to test by replacing it with a new part.
Using a diagnostic scanner to read fault codes is extremely convenient. Last time when my engine warning light came on, the scanner showed a P0715 transmission input shaft speed sensor fault, but it turned out to be a stuck shift solenoid. Nowadays, many vehicle systems can display solenoid operational data streams. For example, if the EGR solenoid opening shows 0% or 100% without movement, there's definitely an issue. You can also listen closely to the solenoid during operation - a normal working solenoid will make a clear 'click-clack' sound. For solenoids with oil circuits, check if the inlet/outlet ports are unobstructed. I've successfully restored many by spraying the valve core with carburetor cleaner.
You can also check the solenoid valve by touch: when the engine is running, feel the valve body temperature. It should be slightly warm under normal conditions; if it's scalding hot, it indicates an internal short circuit. For fuel solenoid valves, you can remove them and perform a blow test—the airflow channel should change when power is applied or cut off, which is normal. If the solenoid valve in the fuel evaporation system is blocked, the fuel tank will build up pressure, and you'll hear a suction sound when opening the fuel cap, indicating a need for inspection. Nowadays, repairing solenoid valves usually involves direct replacement, with unit prices ranging from tens to hundreds, saving labor compared to disassembly and repair. If the AC solenoid valve fails to engage, the compressor clutch won't work at all.
