Kohler 12RES troubleshooting: 84 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Kohler 12RES — full specs, parts & maintenance.
| Code | Meaning | Cause | Remedy |
|---|---|---|---|
| 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 | Input from a customer-supplied switch that closes when the fault is active. The generator set shuts down and will not start when the fault is active (input is grounded). | Check the cause of the auxiliary fault. | |
| HE | 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. | |
| LOP | Shutdown occurs if a low oil pressure condition exists 7 seconds after the engine has reached crank disconnect speed. | 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 | Shutdown occurs after 3 unsuccessful starting attempts. The crank cycle is set for three starting attempts of 15 seconds cranking and 15 seconds rest. The generator set also shuts down after 1 crank attempt if no speed signal is sensed. Shuts down 1 second after the fault is detected. | Check the fuel supply, spark plug, and battery. Check for loose connections. | Contact an authorized distributor/dealer for service if problem continues. |
| OF | Shutdown occurs when the governed frequency exceeds 110% of the system’s frequency setpoint for more than 1 second. This protective becomes active 30 seconds after engine start. | Contact an authorized distributor/dealer for service if problem continues. | |
| OS | Shutdown occurs if the engine speed exceeds 115% of the normal running speed for more than 1 second. | Contact an authorized distributor/dealer for service if problem continues. | |
| OU | Shutdown occurs if the voltage exceeds 120% of the voltage regulator setpoint for more than 1 second. | Contact an authorized distributor/dealer for service if problem continues. | |
| UF | Shutdown occurs when the governed frequency falls 1 Hz below the system’s frequency setpoint for more than 1 second. | Reduce the load and restart the generator set. Contact an authorized distributor/dealer for service if problem continues. | |
| UU | Shutdown occurs if the voltage falls below 80% of the voltage regulator setpoint for more than 1 second. This protective becomes active 30 seconds after engine start. | Reduce the load and restart the generator set. Contact an authorized distributor/dealer for service if problem continues. | |
| HB | Fault code is displayed if the engine starting battery voltage rises above 16 VDC for a 12 VDC system or above 30 VDC for a 24 VDC system for more than 10 seconds when the engine is not running. This fault condition does not inhibit engine starting. | Check the battery rating and condition. Check the battery charger operation. | |
| LB | Fault code is displayed if the engine starting battery voltage falls below 8 VDC for a 12 VDC system or below 16 VDC for a 24 VDC system for more than 10 seconds when the engine is not running. This fault condition does not inhibit engine starting. | Check the battery rating and condition. Check the battery charger operation. | Charge or replace the battery. |
| AF | Indicates a shutdown initiated by pushing the emergency stop switch. | Not used on RES models. | Check the position of the emergency stop button. (TRES models only) |
| HE | High engine temperature shutdown | Shutdown occurs if the engine coolant temperature exceeds the maximum temperature for more than 5 seconds. This function becomes active after the engine reaches the crank disconnect speed. | Check for blocked air inlets and exhaust outlets. |
| 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. |
| 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. |
| 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. | ||
| OF | Overfrequency shutdown | Shutdown occurs when the governed frequency exceeds 110% of the system’s frequency setpoint for more than 5 seconds. This function 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. |
| 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. |
| 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 function 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. |
| 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. | Check the battery rating and condition. Check the battery charger operation. |
| 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. | |
| AF | Auxiliary fault input shutdown | Indicates a shutdown initiated by pushing the emergency stop switch. (TRES models only) | Check the position of the emergency stop button. (TRES models only) |
| Symptom | Cause | Remedy |
|---|---|---|
| Severe electrical equipment damage. | Welding the generator set. | Never weld components of the generator set without first disconnecting the battery, controller wiring harness, and engine electronic control module (ECM). |
| Battery short circuits | 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. | |
| Battery short circuits. | 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. | |
| Generator does not start | Low battery voltage or faulty starter motor | Check the battery and ensure it is fully charged. If necessary, replace the battery. Check the starter motor for proper operation. |
| Gas fuel leaks can cause an explosion. | Check the LPG vapor or natural gas fuel system for leakage by using a soap and water solution with the fuel system test pressurized to 6--8 ounces per square inch (10--14 inches water column). Do not use a soap solution containing either ammonia or chlorine because both prevent bubble formation. A successful test depends on the ability of the solution to bubble. | |
| Battery acid is electrically conductive and corrosive. | Add 500 g (1 lb.) of bicarbonate of soda (baking soda) to a container with 4 L (1 gal.) of water and mix the neutralizing solution. Pour the neutralizing solution on the spilled battery acid and continue to add the neutralizing solution to the spilled battery acid until all evidence of a chemical reaction (foaming) has ceased. Flush the resulting liquid with water and dry the area. | |
| Battery short circuits can cause bodily injury and/or equipment damage. | 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. | |
| Accidental starting | Disconnect the battery cables before working on the generator set. Remove the negative (--) lead first when disconnecting the battery. Reconnect the negative (--) lead last when reconnecting 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. | |
| Fuse blows repeatedly | Replace Auxiliary winding fuse (F1). Contact an authorized distributor/dealer if the fuse blows again. | |
| Generator set master switch in the OFF/RESET position | Move generator set master switch to the AUTO or RUN position. | |
| Red LED stays on for more than 24 hours | One or more defective or damaged cells. | Load test the battery and replace, if necessary. |
| 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. |
| Neither of the LEDs turn on | No AC power available at the battery charger. | Connect AC power or reset the AC breaker on the main panel. |
| Green LED stays on when the battery is known to be low | One or more defective or damaged cells. | Load test the battery and replace, if necessary. |
| The generator set does not crank. | Battery weak or dead, Battery charger fuse blown, Battery connections reversed or poor, Controller fuse (F3) blown, Relay interface board fuse (F2) blown | Check power to the battery charger. Recharge or replace the battery. Replace the fuse. Contact an authorized distributor/dealer for service if fuse blows repeatedly. Check the connections. Replace the fuse. Contact an authorized distributor/dealer for service if fuse blows repeatedly. |
| Severe electrical equipment damage | Welding on generator set | Before welding on the generator set perform the following steps: (1) Remove the battery cables, negative (-) lead first. (2) Disconnect all engine electronic control module (ECM) connectors. (3) Disconnect all generator set controller and voltage regulator circuit board connectors. (4) Disconnect the engine battery-charging alternator connections. (5) Attach the weld ground connection close to the weld location. |
| Generator set does not crank | Weak or dead battery | Recharge or replace battery. If battery is weak or dead, check battery charger fuse, power supply, and operation. |
| Generator set cranks but does not start | No fuel | Open (turn on) manual fuel valve. Check fuel supply tank (LP). |
| Stops suddenly | Fault shutdown | Check for a fault shutdown code on the controller’s LED display. Correct the fault and then move the generator set master switch to OFF/RESET to reset the controller. |
| No fuel | Turn on fuel supply. | |
| Engine overheated | Check air intake, fuel adjustment, oil level, air inlet/outlet. | |
| Low oil pressure (LOP) switch | Attempt startup. If unit shuts down, remove lead from LOP switch and reset controller. A successful restart attempt indicates a faulty LOP shutdown switch. Note: Check engine oil pressure before performing test and/or replacing LOP shutdown switch. | |
| Fuel valve/fuel regulator | Check regulator/valve operation. | |
| Engine overloaded | Reduce electrical load. | |
| Lacks power | Air intake restriction, inadequate cooling. Inspect air intakes and exhaust for obstructions. Check air cleaner. | |
| Generator overloaded | Reduce load. | |
| Engine not running at rated rpm | Check controller settings for unit configuration (UC) and engine type (EC). Adjust governor speed. | |
| Engine power loss | Refer to the Engine Service Manual for troubleshooting and repair instructions. | |
| Governor malfunction or misadjustment | Test/readjust governor. | |
| Low output voltage | Incorrect controller configuration, Incorrect controller voltage settings | Check and adjust the controller configuration parameters. Check and adjust the controller voltage settings. |
| Alternator or control system problem | Perform separate excitation procedure to isolate the problem to the alternator or the control system. Then troubleshoot the alternator or control system components as follows. | |
| No output voltage | AC output circuit breaker open, Alternator or control system problem | Check for AC voltage on the generator side of circuit breaker. If there is AC voltage on the generator side of the breaker, then a problem in the load circuits is causing the line circuit breaker to trip. Check for and correct short circuits or overloading on the load side before resetting the circuit breaker. Perform separate excitation procedure to isolate the problem to the alternator or the control system. Then troubleshoot the alternator or control system components as follows. |
| Open wiring, terminal, or pin in buildup circuit or SCR module circuit | Check continuity. | |
| Brushes problem | Inspect brushes and replace if worn. Check for brushes sticking in brush holder or broken brush spring. | |
| Rotor connections problem | Check for open circuit in rotor connection circuit (leads FN and FP to SCR and RIB). | |
| Rotor slip rings dirty or corroded | Check slip ring condition. | |
| Stator problem | Check voltage and continuity. | |
| Engine not running smoothly | See “Generator set operates erratically,” this table | |
| Broken or damaged vibromount(s) | Check and replace as necessary. | |
| Loose or vibrating sheet metal/housing | Retighten screws, replace rivets. | |
| Exhaust piping or air inlets/outlets not securely installed | Inspect for loose parts and secure if necessary. | |
| Excessive engine/generator vibration | Check, rotor, crankshaft, bearing, etc. (disassembly of engine and/or alternator may be required). | |
| Line circuit breaker trips or fuses blow repeatedly | See Section 4, Troubleshooting, for possible causes | |
| 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. Low or no battery voltage. Check connections. Check the engine starting battery and battery charger. See Figure 4-3. |
| 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. Battery weak or dead Check power to the battery charger. Recharge or replace the battery. Battery connection poor Clean and tighten the battery connections. Spark plug wire connection loose Check the spark plug wires. Low oil pressure shutdown Check the oil level. Fuel pressure insufficient Check the fuel supply and valves. 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. AC circuit breaker tripping because of overload Reduce the load on the generator set. AC circuit breaker tripping because of short circuit Contact an authorized distributor/dealer for service. |
| Generator set stops suddenly. | Low oil pressure shutdown | Check the oil level. Check for signs of oil leaks. Out of fuel Check fuel supply. Overcrank shutdown Reset the controller. If the overcrank fault occurs again, contact an authorized distributor/dealer. |
| Remote stop command received from a remote switch or ATS | Check the remote switch position. | |
| Engine malfunction | Contact an authorized distributor/dealer. | |
| Auxiliary winding fuse (F1) blown | Replace the fuse. Contact an authorized distributor/dealer for service if fuse blows repeatedly. | |
| Low output or excessive drop in voltage. | Generator set overloaded Reduce the load. | |
| Controller fuse (F3) blown | Replace the fuse. If the fuse blows again, contact an authorized distributor/dealer. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Welding the generator set.; Welding on generator set. See the table for the matching fixes.
Documented causes: Low battery voltage or faulty starter motor. See the table for the matching fixes.
Documented causes: One or more defective or damaged cells.. See the table for the matching fixes.