Disconnect the upper solenoid vacuum hose from the vacuum manifold and connect the vacuum pump.
Plug the end of hose #32.
Warm up the engine to operating temperature until the cooling fan comes on.
If the electromagnetic valve holds a vacuum, then see point A), if it does not, then point B).
A) Disconnect the 4-pin connector near the solenoid valve.
Measure the voltage between the White/Yellow (+) and Black (-) terminals on the main wiring harness. If there is voltage, then you should refer to the section on diagnostics of control module inputs.
If there is no voltage, then the solenoid valve should be replaced.
B) Increase engine speed to 2500 rpm and create vacuum.
If the solenoid valve holds a vacuum, then the vacuum line should be checked for proper connection, cracks, plugs, or a disconnected hose.
If the solenoid valve does not hold vacuum, the 4-pin connector near the valve should be disconnected.
Next, measure the voltage between the White/Yellow (+) and Black (-) terminals on the main wiring harness while the engine is running at approximately 2500 RPM.
If there is battery voltage, then the solenoid valve should be replaced.
If there is no voltage, then measure the voltage between the White/Yellow (+) terminals and ground while the engine is running at approximately 2500 rpm.
If there is battery voltage, then the break in the Black conductor between the control box and point G5 should be repaired.
If there is no voltage, then you should check for a break in the White/Yellow wire between the control box and terminal 20 of the control unit. If the wire is normal, then you should refer to the diagnostics of the control module inputs.
[The original is located on the website hondabook]