Honda two-wire float switch.
With oil at the minimum level or higher there will be no continuity (switch open) between the two wires. When the oil level is below the required level there will be continuity (switch closed). The green wire is connected to ground. Many similar switches have only one wire showing. In that case, measure continuity from the one wire to ground on the engine block.
Honda low oil shutdown sensor and indicator light.
This low oil sensor will ground out the primary winding of the ignition coil when it senses the float switch is closed.
Honda low oil shutdown float switch with ground contact.
Honda low oil shutdown float reed switch operation drawing
The float incorporates a small magnet that will hold a reed switch closed when the oil levels falls.
Honda low oil shutdown 'Oil Alert' wiring diagram.
When the oil in the crankcase falls below a specified level the float switch (8) closes providing a path to ground for the yellow wire (Y) of the sensor (6). When this occurs the sensor grounds out the ignition primary lead (Bl) shutting down the engine.
Honda low oil shutdown float switch and sensor pictorial diagram.
The float switch is mounted inside the crankcase. The wires pass through the side of the crankcase above the oil level and are secured with a threaded nipple, O-ring and nut. Replacing the float switch can be very involved. For example, if the engine powers a generator, the generator unit must be removed prior to opening the crankcase cover.
Honda low oil shutdown sensor - 2 wire
The sensor limits the current sent to the float switch from the ignition primary thereby reducing arcing and extending the switch's life. When the float switch closes for a sufficient length of time the sensor connects the primary to ground and latches in that state, preventing intermittent on/off conditions. The sensor is evaluated by process of elimination. If the float switch tests good and the engine runs properly with the sensor disconnected from the ignition primary lead, the sensor is presumed to be bad.
Honda low oil shutdown diaphragm switch pictorial diagram.
A pressure switch (4) is connected to a rubber tube (8) which in turn is connected to a metal tube (6 or 7) that extends into an oil cup. The lower end of the metal tube opens below the acceptable oil level.
Honda low oil shutdown diaphragm switch drawing.
A metal tube extends downward into an oil cup. The oil cup's design helps to minimize oil level fluctuation due to splashing, vibration and tilting. The lower end of the tube opens below the minimum required oil level. When the oil level falls below the minimum required level the tube is exposed to crankcase pressure which rises and falls with the movement of the piston. Although the average pressure in the crankcase is negative (vacuum), the pressure goes positive when the piston is around bottom dead center. A check valve in the switch assembly allows pressure to accumulate against the diaphragm. When sufficient pressure moves the diaphragm, a switch is tripped which grounds out the ignition and the engine is shut down.