Kohler 18RES troubleshooting: 33 fault codes and 66 symptom-cause-remedy entries from the manufacturer's own service documentation.
Kohler 18RES — full specs, parts & maintenance.
| Code | Meaning | Cause | Remedy |
|---|---|---|---|
| HE | High engine temperature shutdown — Shutdown occurs if the engine coolant temperature exceeds the maximum temperature for more than 5 seconds. This protective becomes active after the engine reaches the crank disconnect speed. | Check for blocked air inlets and exhaust outlets. | |
| LO P | Low oil pressure shutdown — Shutdown occurs if a low oil pressure condition exists for more than 5 seconds. This protective becomes active 30 seconds after the engine has reached crank disconnect speed (30 second inhibit). Note: The low oil pressure shutdown does not protect against low oil level. Check the oil level at the engine. | Check for leaks in the lubrication system.; Check the oil level and add oil if the level is low. | |
| OC | Overcrank shutdown — Shutdown occurs after 3 unsuccessful starting attempts. The crank cycle is set for three starting attempts of 15 seconds cranking and 15 seconds rest. | Check the fuel supply, spark plug, and battery.; Check for loose connections.; Contact an authorized distributor/dealer for service if problem continues. | |
| OC | Locked rotor — The generator set also shuts down on OC if no engine rotation is sensed during cranking. Shuts down 3 seconds after the fault is detected. | Contact an authorized distributor/dealer for service if problem continues. | |
| OF | Overfrequency shutdown — Shutdown occurs when the governed frequency exceeds 110% of the system's frequency setpoint for more than 5 seconds. This protective becomes active 10 seconds after engine start (10 second inhibit). | Contact an authorized distributor/dealer for service if problem continues. | |
| OS | Overspeed shutdown — Shutdown occurs if the engine speed exceeds 110% of the normal running speed for more than 0.3 seconds. | Contact an authorized distributor/dealer for service if problem continues. | |
| UF | Underfrequency shutdown — Shutdown occurs if the governed frequency falls below 54 Hz for more than 5 seconds. Shutdown also occurs if the governed frequency falls below 56.5 Hz for more than 60 seconds. This protective becomes active 10 seconds after engine start. (10 second inhibit). | Reduce the load and restart the generator set.; Contact an authorized distributor/dealer for service if problem continues. | |
| UU | Undervoltage shutdown — Shutdown occurs if the voltage falls below 80% of the nominal system voltage for more than 10 seconds. | Reduce the load and restart the generator set.; Contact an authorized distributor/dealer for service if problem continues. | |
| LB | Low battery voltage warning — Fault code is displayed if the engine starting battery voltage falls below 11 VDC for more than 30 seconds when the engine is not running. Not operative during the engine crank cycle, this fault condition does not inhibit engine starting. The fault condition clears when the battery voltage returns to an acceptable level. | Check the battery rating and condition.; Check the battery charger operation.; Charge or replace the battery. | |
| F3 | Controller LED display is off | Controller fuse (F3) is blown. | Replace the fuse. If the fuse blows again, contact the distributor/dealer. |
| F2 | The generator set does not crank. | Fuse F2 blown | Replace the fuse. Contact an authorized distributor/dealer for service if fuse blows repeatedly. |
| F3 | The generator set does not crank. | Fuse F3 blown | Replace the fuse. Contact an authorized distributor/dealer for service if fuse blows repeatedly. |
| F1 | No AC output. | Auxiliary winding fuse (F1) blown | Replace the fuse. Contact an authorized distributor/dealer for service if fuse blows repeatedly. |
| F3 | Generator set stops suddenly. | Controller fuse (F3) blown | Replace the fuse. If the fuse blows again, contact the distributor/dealer. |
| F1 | Generator set stops suddenly. | Auxiliary winding fuse (F1) blown | Replace the fuse. Contact an authorized distributor/dealer for service if fuse blows repeatedly. |
| High engine temperature | Engine runtime, hours | ||
| Low battery voltage | Crank cycle status | ||
| Overcrank | Remote two-wire start/stop capability | ||
| Overfrequency | Digital voltage regulation: ±1.5% RMS no-load to full-load | ||
| Overspeed | Automatic start for programmed cranking cycle | ||
| Underfrequency | Master control switch mounted on the junction box: Run/Off-Reset/Auto | ||
| Undervoltage | Upgradeable application software | ||
| AF | Auxiliary fault input shutdown — Indicates a shutdown initiated by pushing the emergency stop switch. (TRES models only) Not used on RES models. | Check the position of the emergency stop button. (TRES models only) | |
| LOP | Low oil pressure shutdown — Shutdown occurs if a low oil pressure condition exists for more than 5 seconds. This function becomes active 30 seconds after the engine has reached crank disconnect speed (30 second inhibit). Note: The low oil pressure shutdown does not protect against low oil level. Check the oil level at the engine. | Check for leaks in the lubrication system.; Check the oil level and add oil if the level is low. | |
| OU | Overvoltage shutdown — Shutdown occurs if the voltage exceeds 120% of the system nominal voltage for more than 2 seconds. | Contact an authorized distributor/dealer for service if problem continues. | |
| HB | High battery voltage warning — Fault code is displayed if the engine starting battery voltage rises above 16 VDC for more than 30 seconds when the engine is running. Not operative during the engine crank cycle, this fault condition does not inhibit engine starting. The fault condition clears when the battery voltage returns to an acceptable level. | Check the battery rating and condition.; Check the battery charger operation. | |
| F2 | The generator set does not crank — Fuse F2 blown | Fuse F2 blown | Replace the fuse. Contact an authorized distributor/dealer for service if fuse blows repeatedly. |
| F3 | The generator set does not crank — Fuse F3 blown | Fuse F3 blown | Replace the fuse. Contact an authorized distributor/dealer for service if fuse blows repeatedly. |
| F1 | No AC output — Auxiliary winding fuse (F1) blown | Auxiliary winding fuse (F1) blown | Replace the fuse. Contact an authorized distributor/dealer for service if fuse blows repeatedly. |
| F3 | Generator set stops suddenly — Controller fuse (F3) blown | Controller fuse (F3) blown | Replace the fuse. If the fuse blows again, contact an authorized distributor/dealer. |
| F1 | Generator set stops suddenly — Auxiliary winding fuse (F1) blown | Auxiliary winding fuse (F1) blown | Replace the fuse. Contact an authorized distributor/dealer for service if fuse blows repeatedly. |
| F2 | The battery is discharged, but the charger has power and is operating. — Blown fuse. | Blown fuse. | Check the 5-amp fuse F2 (5A-T) inside the battery charger and replace if necessary. Check inline fuse F4 and replace if necessary. |
| Locked rotor | The generator set also shuts down on OC if no engine rotation is sensed during cranking. Shuts down 3 seconds after the fault is detected. |
| Symptom | Cause | Remedy |
|---|---|---|
| Controller LED display is off | No power to the controller: The generator set has not run for 48 hours or longer and the controller has powered down. | Controller display will automatically activate when a remote start command is received or the generator set master switch is moved to the RUN position. See Section 2.3. |
| Controller LED display is off | Low or no battery voltage. | Check connections.; Check generator set battery and battery charger. See Figure 5-2. |
| Controller LED display is off | Generator set master switch is in the OFF/RESET position. | Move generator set master switch to the AUTO or RUN position. In AUTO, the display will not turn on until the first start command is received. |
| Controller LED display is off | Generator set master switch in AUTO but no start command has been received since last controller reset. | Controller display will activate when a remote start command is received or the generator set master switch is moved to the RUN position. Use the remote switch to start generator set and activate the controller display, if desired. See Section 2.2.2. |
| The generator set does not crank. | Fault shutdown | Check for a fault code on the controller display. See Section 2.6. |
| The generator set does not crank. | Battery weak or dead | Check power to the battery charger.; Recharge or replace the battery. |
| The generator set does not crank. | Battery charger fuse blown | Replace the fuse. Contact an authorized distributor/dealer for service if fuse blows repeatedly. |
| The generator set does not crank. | Battery connections reversed or poor | Check the connections. |
| The generator set does not crank. | Generator set master switch in the OFF position | Move the master switch to AUTO for remote start or to RUN for local start. |
| The generator set cranks but does not start, starts hard, lacks power, or operates erratically. | Air cleaner clogged | Clean and/or replace the air cleaner. |
| The generator set cranks but does not start, starts hard, lacks power, or operates erratically. | Battery weak or dead | Check power to the battery charger.; Recharge or replace the battery. |
| The generator set cranks but does not start, starts hard, lacks power, or operates erratically. | Battery connection poor | Clean and tighten the battery connections. |
| The generator set cranks but does not start, starts hard, lacks power, or operates erratically. | Spark plug wire connection loose | Check the spark plug wires. |
| The generator set cranks but does not start, starts hard, lacks power, or operates erratically. | Low oil pressure shutdown | Check the oil level. |
| The generator set cranks but does not start, starts hard, lacks power, or operates erratically. | Fuel pressure insufficient | Check the fuel supply and valves. |
| The generator set cranks but does not start, starts hard, lacks power, or operates erratically. | Engine malfunction | Contact the distributor/dealer. |
| No AC output. | AC circuit breaker in the OFF position | Place the circuit breaker in the ON position. |
| No AC output. | AC circuit breaker tripping because of overload | Reduce the load on the generator set. |
| No AC output. | AC circuit breaker tripping because of short circuit | Contact an authorized distributor/dealer for service. |
| Low output or excessive drop in voltage. | Generator set overloaded | Reduce the load. |
| Generator set stops suddenly. | Low oil pressure shutdown | Check the oil level. |
| Generator set stops suddenly. | Out of fuel | Check fuel supply. |
| Generator set stops suddenly. | Overcrank shutdown | Reset the controller. If the overcrank fault occurs again, contact the distributor/dealer. |
| Generator set stops suddenly. | Overspeed shutdown | Reset the controller. If the overspeed fault occurs again, contact the distributor/dealer. |
| Generator set stops suddenly. | Generator set master switch in the OFF/RESET position | Move the switch to the correct position (RUN or AUTO). |
| Generator set stops suddenly. | Remote stop command received from a remote switch or ATS | Check the remote switch position. |
| Generator set stops suddenly. | Engine malfunction | Contact the distributor/dealer. |
| Red LED stays on for more than 24 hours | One or more inoperative or damaged cells. | Load test the battery and replace, if necessary |
| Red LED stays on for more than 24 hours | Battery charger has reduced its output voltage below the normal level due to a DC overload or a DC short. | Remove the source of the overload or short. Disconnect the battery charger's black (NEGATIVE) ring terminal from the battery. Reapply AC power and the green LED only should now light. |
| Red LED stays on for more than 24 hours | Onboard DC systems are drawing more current than the battery charger can replace. | Turn off all DC equipment while charging. |
| Red and green LEDs stay on for more than 24 hours | Onboard DC systems are drawing between 1.5 and 5 amps. | Turn off all DC equipment while charging. |
| Red and green LEDs stay on for more than 24 hours | One or more inoperative or damaged cells. | Load test the battery and replace, if necessary |
| Red and green LEDs stay on for more than 24 hours | Extremely low AC voltage at the battery charger. | Apply a higher AC voltage source or reduce the length of the extension cord. |
| Green LED stays on when the battery is known to be low | Open DC output fuse. | Replace AGS-10 fuse. |
| Green LED stays on when the battery is known to be low | Faulty or contaminated terminal connections. | Clean and tighten or repair all terminal connections. |
| Green LED stays on when the battery is known to be low | One or more inoperative or damaged cells. | Load test the battery and replace, if necessary. |
| Neither of the LEDs turn on when the AC power is applied | No AC power available at the battery charger. | Connect AC power or reset the AC breaker on the main panel. |
| Neither of the LEDs turn on when the AC power is applied | Component failure. | Replace battery charger. |
| Controller LED display is off | No power to the controller: Controller fuse (F3) is blown. | Replace the fuse. If the fuse blows again, contact an authorized distributor/dealer. |
| Controller LED display is off | The controller is in sleep mode. See Section 2.5.2. | Controller display will activate when a remote start command is received or the generator set master switch is moved to the RUN position. Use the remote switch to start generator set and activate the controller display, if desired. See Section 2.5.; Controllers with application code version 1.13 or higher can be configured to enable or disable the sleep mode. See the generator set Installation Manual for instructions. |
| The generator set does not crank | Fault shutdown | Check for a fault code on the controller display. See Section 2.7. |
| The generator set does not crank | Battery weak or dead | Check power to the battery charger; Recharge or replace the battery. |
| The generator set does not crank | Battery charger fuse blown | Replace the fuse. Contact an authorized distributor/dealer for service if fuse blows repeatedly. |
| The generator set does not crank | Battery connections reversed or poor | Check the connections. |
| The generator set does not crank | Generator set master switch in the OFF position | Move the master switch to AUTO for remote start or to RUN for local start. |
| The generator set cranks but does not start, starts hard, lacks power, or operates erratically | Air cleaner clogged | Clean and/or replace the air cleaner. |
| The generator set cranks but does not start, starts hard, lacks power, or operates erratically | Battery weak or dead | Check power to the battery charger; Recharge or replace the battery. |
| The generator set cranks but does not start, starts hard, lacks power, or operates erratically | Battery connection poor | Clean and tighten the battery connections. |
| The generator set cranks but does not start, starts hard, lacks power, or operates erratically | Spark plug wire connection loose | Check the spark plug wires. |
| The generator set cranks but does not start, starts hard, lacks power, or operates erratically | Low oil pressure shutdown | Check the oil level. |
| The generator set cranks but does not start, starts hard, lacks power, or operates erratically | Fuel pressure insufficient | Check the fuel supply and valves. |
| The generator set cranks but does not start, starts hard, lacks power, or operates erratically | Engine malfunction | Contact an authorized distributor/dealer. |
| No AC output | AC circuit breaker in the OFF position | Place the circuit breaker in the ON position. |
| No AC output | AC circuit breaker tripping because of overload | Reduce the load on the generator set. |
| No AC output | AC circuit breaker tripping because of short circuit | Contact an authorized distributor/dealer for service. |
| Low output or excessive drop in voltage | Generator set overloaded | Reduce the load. |
| Generator set stops suddenly | Low oil pressure shutdown | Check the oil level. Check for signs of oil leaks. |
| Generator set stops suddenly | Out of fuel | Check fuel supply. |
| Generator set stops suddenly | Overcrank shutdown | Reset the controller. If the overcrank fault occurs again, contact an authorized distributor/dealer. |
| Generator set stops suddenly | Overspeed shutdown | Reset the controller. If the overspeed fault occurs again, contact an authorized distributor/dealer. |
| Generator set stops suddenly | Generator set master switch in the OFF/RESET position | Move the switch to the correct position (RUN or AUTO). |
| Generator set stops suddenly | Remote stop command received from a remote switch or ATS | Check the remote switch position. |
| Generator set stops suddenly | Engine malfunction | Contact an authorized distributor/dealer. |
| Green LED is off and there is no output voltage. | No power to the battery charger. | Check the power supply to the charger. Check the upstream circuit breakers and fuses. Check fuse FS (1A-T) inside the battery charger. |
| Abnormal low voltage, charger is operating. | The battery completely discharged and the charger is operating at the current limit. | Disconnect the battery and verify that the charger output is 13.2 VDC. Reconnect the charger and allow time for the battery to recharge. The battery voltage should rise gradually. Test the battery. |
| Battery short circuit | Disconnect the battery before generator set installation or maintenance. Remove all jewelry before servicing the equipment. Use tools with insulated handles. Remove the negative (--) lead first when disconnecting the battery. Reconnect the negative (--) lead last when reconnecting the battery. Never connect the negative (--) battery cable to the positive (+) connection terminal of the starter solenoid. Do not test the battery condition by shorting the terminals together. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Low oil pressure shutdown; Out of fuel; Overcrank shutdown; Controller fuse (F3) blown. See the table for the matching fixes.
Documented causes: Air cleaner clogged; Battery weak or dead; Battery connection poor; Spark plug wire connection loose. See the table for the matching fixes.
Documented causes: Fault shutdown; Battery weak or dead; Battery charger fuse blown; Battery connections reversed or poor. See the table for the matching fixes.