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Kubota BX23, BX23S, BX24, BX25, BX25D electrical system - Checking and adjusting

Battery

Checking battery voltage - Stop the Kubota BX23, BX23S, BX24, BX25, BX25D engine and turn the main switch OFF. Connect the COM (-) lead of the voltmeter to the battery's negative terminal post and the (+) lead to the positive terminal post, and measure the battery voltage. If the battery voltage is less than the factory specification, check the battery specific gravity and recharge the battery. Battery voltage - More than 12 V. Checking battery terminal connection - Turn the main switch ON, and turn on the head light. Measure the voltage with a voltmeter across the battery's positive terminal post and the cable terminal, and the voltage across the battery's negative terminal post and the chassis. If the measurement exceeds the factory specification, clean the battery terminal posts and cable clamps, and tighten them firmly. Potential difference - Less than 0.1 V.

Kubota BX23, BX23S, BX24, BX25, BX25D - Starter and glow plug

Testing starter

Testing starter magnet switch (pull-in, holding coils) - Remove the motor from the starter housing. Prepare a 6 V battery for the test. Connect jumper leads from the battery negative terminal to the housing and the starter C terminal. The plunger should be attracted and the pinion gear should pop out when a jumper lead is connected from the battery positive terminal to the S terminal. Disconnect the jumper lead to the starter C terminal. Then the pinion gear should remain popped out. Checking main switch continuity at start position - Set and hold the main switch key at the START position. Measure the resistance with an ohmmeter across the B terminal and the G terminal, across the B terminal and the ST terminal, and across the B terminal and the ACC terminal. If 0 ohm is not indicated, these contacts of the main switch are damaged. Disconnect the battery negative cable from the battery. Disconnect the battery positive cable and the leads from the starter. Remove the starter from the engine. Disconnect the connecting lead from the starter C terminal. Connect a jumper lead from the connecting lead to the battery positive terminal post. Connect a jumper lead momentarily between the starter motor housing and the battery negative terminal post. If the motor does not operate, check the motor.

Checking glow plug lead terminal voltage

Checking glow plug lead terminal voltage (Kubota BX23, BX23S, BX24, BX25, BX25D) - Disconnect the wiring lead from the glow plug after turning the main switch OFF. Turn the main switch key to the PREHEAT position, and measure the voltage between the lead terminal and the chassis. Turn the main switch key to the START position, and measure the voltage with a voltmeter between the lead terminal and the chassis. If the voltage at either position differs from the battery voltage, the wiring harness or main switch is damaged. Disconnect the lead from the glow plugs. Measure the resistance with an ohmmeter between the glow plug terminal and the chassis. If 0 ohm is indicated, the screw at the tip of the glow plug and the housing are short-circuited. If the factory specification is not indicated, the glow plug is damaged.

Kubota BX23, BX23S, BX24, BX25, BX25D - Safety switch

Checking PTO shift lever switch continuity

Remove the left rear wheel. Remove the PTO shift lever switch. Measure the resistance with an ohmmeter across the switch terminals. If the resistance values specified below are not indicated, the safety switch is damaged. Checking HST neutral switch continuity - Remove the right rear wheel. Remove the HST neutral switch. Measure the resistance with an ohmmeter across the HST neutral switch terminals. If the resistance values specified below are not indicated, the safety switch is damaged.

Checking main switch continuity at on position

Set the main switch to the ON position. Measure the resistance with an ohmmeter across the B terminal and the ACC terminal. If 0 ohm is not indicated, the B-ACC contact of the main switch is damaged. Checking main switch continuity at preheat position - Set and hold the main switch key at the PREHEAT position. Measure the resistance with an ohmmeter across the B terminal and the G terminal, and measure the resistance across the B terminal and the ACC terminal. If 0 ohm is not indicated, these contacts of the main switch are damaged.

Checking seat switch

Checking seat switch and seat turnover switch continuity (Kubota BX23, BX23S, BX24, BX25, BX25D) - Disconnect the 2P connectors from the seat switch and the seat turnover switch. Remove the seat switch and seat turnover switch. Connect the circuit tester to the terminals. Measure the resistance between terminals. If continuity is not as shown below, the switch is damaged. Replace it. Measure the resistance between terminals. If continuity is not as shown below, the switch is damaged. Replace it.

Kubota BX23, BX23S, BX24, BX25, BX25D - Electrical functions

Precautions on handling electrical connectors

When disconnecting connectors, grasp the body of the connector and pull it out; do not pull on the wiring harness. If the connector is the locking type, release the lock and then pull to disconnect. When removing a connector's plastic cover (for water protection) to inspect it, be careful not to let any water get in the connector. If water does get in, dry it thoroughly before reassembling the connector and putting its plastic cover securely in place. Straighten any bent connector terminals and make sure none are sticking out or missing. Also make sure there is no corrosion on the connector's terminals before connecting it. When connecting a locking connector, be sure to press it in until you hear it click and then pull gently on the harness close to the connector and make sure the harness does not come out.

Electrical circuit of starting system

When the main switch is turned to the GLOW position, the terminal BAT is connected to the terminal ON and AC. The glow plugs become red-hot, and the preheat indicator lamp also lights on while preheating. When the main switch is then turned to the START position with the safety switches on, the terminal BAT is connected to the terminals GLOW and ST. Consequently, battery current flows to the starter motor and start the engine. The main switch automatically returns to the ON position, the terminal BAT is connected only to the terminal GLOW, thereby causing the starting circuit to be opened, stopping the starter motor. When the main switch turned from the ON position to the OFF position, the fuel cut-off solenoid moves the fuel injection pump control rack to the no fuel injection position and stops the engine. The OPC timer equipped is the operator presence control (OPC) system which automatically stops the engine in approximately one second when operator stands from the seat while shifting the PTO clutch lever and range gear shift lever.

Function of relay

A relay is an electrically operated switch. Relays are used where it is necessary to control a circuit by a lowpower signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. Current flowing from switch to relay winding cause ON (Close) or OFF (Open) of mechanical contact points. When current is applied to the winding (energized), a magnetic field pushes the contact lever and normally open terminal is connected.

Function of starter

The reduction system is used planetary gears, and the speed of gear shaft is reduced to approximately one-fifth of the armature shaft. The pinion gear is pushed against the ring gear with the overrunning clutch by the drive lever.

Function of glow plug

This plug is a two-material type QGS (Quick Glow System) for quick temperature rise, and has selfcontrolling function as well as excellent durability. The heater connected in series to the heater, which also functions as the resistor, is incorporated in the sheath tube of the super glow plug. The resistance of this heater cum resistor is small when the temperature is low, while the resistance becomes large when the temperature rises. Therefore, because sufficient current is flown to the heater during the initial period of energization, the temperature rises quickly and the resistance grows with the rise in the temperature of the resistor, the flowing current is reduces to prevent the heater from being heated. The ignition point is in the area of 2 to 3 mm (0.079 to 0.118 in.) from the tip of the plug in order to reduce its projection into the combustion chamber.

Function of safety switch

The safety switch is electrically closed in normal condition (normally closed type). The switch operates as sensor detecting and transmitting the position of HST pedal, PTO lever, independent PTO lever, and seat to engine stop solenoid.

Function of fuel pump

An electromagnetic fuel pump uses a transistor that causes the pump to start pumping fuel when the main switch is turned to the ON position. Therefore, fuel is supplied to the fuel injection pump regardless of engine speed. This pump is driven by the battery. It can therefore be operated even with the engine being stopped. OPC (Operator Presence Control) system.

Electrical circuit of OPC timer

When sitting on the operator's seat with the main switch is in the ON position, the battery voltage passes to the seat switch and OPC timer, and keep the solenoid relay. When standing up from the operator's seat, the circuit from the seat switch to the OPC timer is cut. However, if the PTO lever (or the speed control pedal) are set at NEUTRAL position, the circuit from the battery to the solenoid relay is formed with the PTO switch (or HST switch). When standing up from the operator's seat while shifting the levers, the circuit from the battery to the solenoid relay is cut, and the engine is stopped by function of the solenoid. The seat switch has two positions. When the operator's seat is occupied, the switch contact point is at ON position. When the operator's seat is not occupied, its contact point is at OFF position. OPC timer is located electrically at between the seat switch and the solenoid relay. When the current supply from the seat switch is cut, the OPC timer adopted for the OPC system has kept the state of ON position for approximately one second.

Electrical circuit for charging system

Function of IC regulator (3P connector type) - 3P connector is connected to the IC regulator. 3P connector consists of three leads, L (blue) lead, RY (red / yellow) lead, and WR (white / red) lead. L (blue) lead is a lead to transmit the pulse from the alternator to hour meter and tachometer. When the main switch is in the ON position, the hour meter indicates operated hours. While the engine operates, the tachometer indicates the present engine revolutions. RY (red / yellow) lead is a lead to chassis. WG (white / green) lead is a lead to the charge lamp.

Function of oil pressure switch

The oil pressure switch is mounted on the cylinder block and is led to the lubricating oil passage. When the oil pressure falls below the specified value, the oil pressure-warning lamp lights.

At the proper oil pressure

When the engine is started and as the proper oil pressure builds, the diaphragm is pushed up. This separates the contact rivet and breaks the circuit, causing the lamp to go out. At lower oil pressure, 49 kPa (0.50 kgf/cm2, 7.1 psi) or less - If the oil pressure drops, the resulting deflection of the diaphragm will close the contact rivet and again complete the circuit. The lighted lamp warns that the pressure of the lubricating system has dropped below the pressure setting.