The C frequency solenoid valve is activated when the engine speed is above 730 rpm or the engine speed is below 730 rpm and the coolant temperature is above 60°C. It manages the vacuum for the throttle regulator.
With the lower solenoid vacuum hose off the manifold, connect the vacuum pump. Disconnect the upper solenoid valve vacuum hose from the triple junction and 2-pin connector near the valve, apply a vacuum.
If the valve does not hold vacuum, replace the valve, otherwise connect a pressure gauge to the upper vacuum hose.
Connect battery power to the 2-pin connector as shown.
Create a vacuum. If the sensor does not show vacuum, replace the solenoid valve, otherwise, disconnect the battery from the connector.
If vacuum is still visible on the gauge, replace the valve, otherwise reconnect the 2-pin connector and hose.
Start the engine and let it warm up so that the cooling fan turns on. Measure the voltage between 21 (blue/red (+)) and 32 (black (-)) control unit outputs (connector is shown in Fig. 43).
If the voltage is different from 56V - refer to the diagnostics section of the inputs of the control modules, otherwise check the blue / red or black conductors for an open circuit.