I have a 315bl excavator. Engine intermittently shut off on its own, but will start back up without a problem. Now

The shutdown solenoid may be the source of your problem. It could be sticking linkage or a bad timer. Below is a simplified layout of the circuit.

Starting And Charging System Schematic
(1) Disconnect switch. (2) Batteries. (3) Power circuit. (4) Breaker 1. (5) Main relay. (6) Fuse box. (7) Low current circuit. (9) Cigar lighter. (10) Starter control relay. (11) Starter switch. (12) Neutral start switch. (13) Cab heater. (14) Air conditioner. (15) Lights. (16) Windshield wiper. (17) Windshield washer. (18) Start/stop circuit. (19) Starter motor. (20) Starter relay. (21) Alternator. (22) Horn. (23) Controller. (24) Switch panel. (25) Shut down solenoid. (26) Heater control unit. (27) Glow plug. (28) Charging circuit. (29) Timer relay. (30) Neutral start relay. (31) Battery breaker. (32) Breaker 2. (33) Breaker 3. (34) Fan relay. (35) Shut down timer. (36) Heater relay.

Here is a brief description of the systems.

The starting and charging system consists of power circuit (3), start/stop circuit (18), charging circuit (28) and low current circuit (7).

For details of the entire electrical system, make reference to the Electrical System Schematic module in the machine Service Manual.

NOTE: The electrical circuits can only be activated when disconnect switch (1) is in the ON position.

Power Circuit

This circuit supplies power to electric components and includes battery (2), disconnect switch (1), battery breaker (31), breaker 1 (4), breaker 2 (32), breaker 3 (33) and main relay (5).

Start/Stop Circuit

This circuit starts/stops the engine and includes starter control relay (10), starter motor (19), starter relay (20), timer relay (29), starter switch (11), shut down solenoid (25), neutral start relay (30), neutral start switch (12) and shut down timer (35).

Start Aid Circuit

Some machines are equipped with starting aid for cold weather starting purposes. The start aid circuit consists of glow plug (27), heater control unit (26) and heater relay (36).

Charging Circuit

This circuit uses alternator (21) to charge battery (2) during engine operation and to supply current to low current circuit (7) through fuse box (6).

Low Current Circuit

This circuit distributes power to several low current components. By operating switch panel (24), this circuit puts on lights (15) installed at chassis, cab and boom. Also, this circuit controls continuous or intermittent operation of the windshield wiper (16).

This is a description of the start and stop circuit.

Start/Stop Circuit Schematic
(2) Battery. (10) Starter control relay. (11) Starter switch. (12) Neutral start switch. (19) Starter motor. (20) Starter relay. (21) Alternator. (25) Shut down solenoid. (29) Timer relay. (30) Neutral start relay. (42) Starter solenoid. (43) Shut down timer.

When starter switch (11) is placed in ON position (39) with the hydraulic activation control lever in LOCKED position, there is current flow through timer relay (29) and neutral start switch (12) to neutral start relay (30). The coil of neutral start relay (30) is energized to be ready for the start operation. When starter switch (11) is placed in START position (40), there is current flow through neutral start relay (30) to starter relay (20). The starter relay contacts are closed and there is current flow to terminal S of starter solenoid (42) from starter relay.

NOTE: If switch (11) is placed in the ON position with the hydraulic activation control lever in UNLOCKED position, no current flows to starter relay (20) and the engine will not start.

When current flows to terminals of starter solenoid (42), contacts are closed and strong current flows from (+) terminal of battery (2) to B terminal of starter solenoid (42), which rotates motor (19) to start the engine.

Once the engine starts, alternator (21) begins to generate electricity. Current signal is sent from P terminal of starter control relay (10). Terminal S of starter control relay (10) opens to turn the coil of starter relay (20) OFF. Starter motor (19) stops its rotation, which prevents the motor from being damaged due to over rotation.

When the starter switch is placed in OFF position (41), shut timer timer (43) supplies power for a certain period. Shut down solenoid (25) starts to move and stops fuel supply to the engine for 6 seconds, which stops the engine. After the 6 seconds is over, the governor actuator opens fuel rack to make restart possible. If starter switch (11) is placed in the ON position before the 6 seconds pass, the governor opens the fuel rack at that time.

Check the linkage first, spray it heavily with penetrating oil. Look in the fuse panel and replace the fuse even if it looks ok. Clean any corrosion away from contacts. If the circuit appears to be normal, then replace the solenoid.