Kohler 125REZGT troubleshooting: 129 symptom-cause-remedy entries from the manufacturer's own service documentation.
Kohler 125REZGT — full specs, parts & maintenance.
| Symptom | Cause | Remedy |
|---|---|---|
| Does not crank | Controller and Emergency Stop Switch | |
| Cranks but does not start | Controller and Emergency Stop Switch | |
| Does not crank | Controller circuit board(s) inoperative | Replace the controller. |
| Cranks but does not start | Controller circuit board(s) inoperative | Replace the controller. |
| Does not crank | Controller circuit board(s) wiring fault | Check the wiring. |
| Does not crank | Controller fault | Troubleshoot the controller. |
| Cranks but does not start | Controller fault | Troubleshoot the controller. |
| Starts hard | Controller fault | Troubleshoot the controller. |
| Does not crank | Controller internal fuse blown | Check for battery power to the circuit board. If fuse does not auto-reset troubleshoot the controller and wiring. |
| Cranks but does not start | Controller internal fuse blown | Check for battery power to the circuit board. If fuse does not auto-reset troubleshoot the controller and wiring. |
| Displays error message/locks up | Controller master control buttons inoperative | Replace the controller master control button circuit board. |
| Does not crank | Controller master control button in the OFF/RESET mode | Press the controller master control RUN or AUTO button. |
| Does not crank | Engine start circuit open | Press the controller master control RUN button to test the generator set. Troubleshoot the auto start circuit and time delays. |
| Cranks but does not start | Engine start circuit open | Press the controller master control RUN button to test the generator set. Troubleshoot the auto start circuit and time delays. |
| Does not crank | Emergency stop switch activated, if equipped | Reset the emergency stop switch. |
| Cranks but does not start | Emergency stop switch activated, if equipped | Reset the emergency stop switch. |
| No or low output voltage | Voltage regulation inoperative | Replace the junction box sensing fuses. If the fuse blows again, troubleshoot the controller. |
| Displays error message/locks up | Controller firmware error | Review the controller display troubleshooting chart. |
| Displays error message/locks up | Controller communication error | Verify that RS-485 cable “shield” wire is connected on only one end. |
| No or low output voltage | AC output circuit breaker open | Reset the breaker and check for AC voltage at the generator set side of the circuit breaker. |
| Does not crank | Transfer switch test switch in the OFF position | Move the transfer switch test switch to the AUTO position. |
| Does not crank | Transfer switch fails to transfer load | Move the ATS test switch to the AUTO position. Troubleshoot the transfer circuit and time delays. |
| No or low output voltage | Wiring, terminals, or pin in the exciter field open | Check for continuity. |
| No or low output voltage | Main field (rotor) inoperative (open or grounded) | Test and/or replace the rotor. |
| No or low output voltage | Stator inoperative (open or grounded) | Test and/or replace the stator. |
| Excessive or abnormal noise | Vibration excessive | Tighten loose components. |
| No or low output voltage | Vibration excessive | Tighten loose components. |
| No or low output voltage | Voltage regulator settings incorrect | Adjust the voltage regulator. |
| Does not crank | Battery connections loose, corroded, or incorrect | Verify that the battery connections are correct, clean, and tight. |
| Cranks but does not start | Battery connections loose, corroded, or incorrect | Verify that the battery connections are correct, clean, and tight. |
| Does not crank | Battery weak or dead | Recharge or replace the battery. The spec sheet provides recommended battery CCA rating. |
| Cranks but does not start | Battery weak or dead | Recharge or replace the battery. The spec sheet provides recommended battery CCA rating. |
| Does not crank | Starter/starter solenoid inoperative | Replace the starter or starter solenoid. |
| Cranks but does not start | Starter/starter solenoid inoperative | Replace the starter or starter solenoid. |
| Does not crank | Engine harness connector(s) not locked tight | Disconnect the engine harness connector(s) then reconnect it to the controller. |
| Cranks but does not start | Engine harness connector(s) not locked tight | Disconnect the engine harness connector(s) then reconnect it to the controller. |
| Does not crank | Fault shutdown | Reset the fault switches and troubleshoot the controller. |
| Cranks but does not start | Fault shutdown | Reset the fault switches and troubleshoot the controller. |
| Does not crank | Air cleaner clogged | Clean or replace the filter element. |
| Cranks but does not start | Air cleaner clogged | Clean or replace the filter element. |
| Starts hard | Air cleaner clogged | Clean or replace the filter element. |
| Lacks power | Air cleaner clogged | Clean or replace the filter element. |
| Does not crank | Compression weak | Check the compression. |
| Cranks but does not start | Compression weak | Check the compression. |
| Starts hard | Compression weak | Check the compression. |
| Lacks power | Compression weak | Check the compression. |
| High fuel consumption | Compression weak | Check the compression. |
| Stops suddenly | Engine overload | Reduce the electrical load. See the generator set spec sheet for wattage specifications. |
| Lacks power | Engine overload | Reduce the electrical load. See the generator set spec sheet for wattage specifications. |
| Excessive or abnormal noise | Exhaust system leak | Inspect the exhaust system. Replace the inoperative exhaust system components. |
| Excessive or abnormal noise | Exhaust system not securely installed | Inspect the exhaust system. Tighten the loose exhaust system components. |
| Starts hard | Governor inoperative | Adjust the governor. |
| Lacks power | Governor inoperative | Adjust the governor. |
| Overheats | Governor inoperative | Adjust the governor. |
| Excessive or abnormal noise | Governor inoperative | Adjust the governor. |
| Starts hard | Valve clearance incorrect | Adjust the valves. |
| Lacks power | Valve clearance incorrect | Adjust the valves. |
| Does not crank | Engine ECM and/or sensors | Troubleshoot the engine ECM and/or sensors. |
| Cranks but does not start | Engine ECM and/or sensors | Troubleshoot the engine ECM and/or sensors. |
| Starts hard | Engine ECM and/or sensors | Troubleshoot the engine ECM and/or sensors. |
| Lacks power | Engine ECM and/or sensors | Troubleshoot the engine ECM and/or sensors. |
| High fuel consumption | Engine ECM and/or sensors | Troubleshoot the engine ECM and/or sensors. |
| Overheats | Air openings clogged | Clean the air openings. |
| Overheats | Coolant level low | Restore the coolant to normal operating level. |
| Overheats | Cooling water pump inoperative | Tighten or replace the belt. Replace the water pump. |
| Overheats | High temperature shutdown | Allow the engine to cool down. Then troubleshoot the cooling system. |
| Overheats | Low coolant level shutdown, if equipped | Restore the coolant to normal operating level. |
| Overheats | Thermostat inoperative | Replace the thermostat. |
| Cranks but does not start | Fuel tank empty or fuel valve shut off | Add fuel and move the fuel valve to the ON position. |
| Starts hard | Fuel tank empty or fuel valve shut off | Add fuel and move the fuel valve to the ON position. |
| Stops suddenly | Fuel tank empty or fuel valve shut off | Add fuel and move the fuel valve to the ON position. |
| Lacks power | Fuel tank empty or fuel valve shut off | Add fuel and move the fuel valve to the ON position. |
| Cranks but does not start | Fuel filter restriction | Clean or replace the fuel filter. |
| Starts hard | Fuel filter restriction | Clean or replace the fuel filter. |
| Stops suddenly | Fuel filter restriction | Clean or replace the fuel filter. |
| Lacks power | Fuel filter restriction | Clean or replace the fuel filter. |
| Cranks but does not start | Fuel solenoid inoperative | Troubleshoot the fuel solenoid. |
| Stops suddenly | Oil level low | Restore the oil level. Inspect the generator set for oil leaks. |
| Low oil pressure | Oil level low | Restore the oil level. Inspect the generator set for oil leaks. |
| Excessive or abnormal noise | Oil level low | Restore the oil level. Inspect the generator set for oil leaks. |
| Stops suddenly | Low oil pressure shutdown | Check the oil level. |
| Starts hard | Crankcase oil type incorrect for ambient temperature | Change the oil. Use oil with a viscosity suitable for the operating climate. |
| Lacks power | Crankcase oil type incorrect for ambient temperature | Change the oil. Use oil with a viscosity suitable for the operating climate. |
| Overheats | Crankcase oil type incorrect for ambient temperature | Change the oil. Use oil with a viscosity suitable for the operating climate. |
| High fuel consumption | Crankcase oil type incorrect for ambient temperature | Change the oil. Use oil with a viscosity suitable for the operating climate. |
| Display is black | No/low battery charge | Recharge/replace battery |
| Display shows single segment | Low battery voltage | Recharge battery |
| Display shows an error message | Controller firmware or pushbutton/rotary selector dial entry error | Review the System Fault Shutdown Lamp With Digital Displays section |
| Display locks up | No/low battery charge | Recharge/replace battery |
| Output voltage ramps | Defective exciter winding | Troubleshoot alternator components |
| Output voltage unstable | Voltage regulation calibration incorrect | Readjust voltage regulation |
| Unable to change voltage and current calibrations | Calibration not enabled | Enable calibration in Generator Metering section 2.6.3 Calibration Submenu |
| Unable to find volt select menu | Volt select not enabled | Enable volt select in SiteTech |
| Trailer is unstable or noisy during towing. | Tire(s) worn or damaged | Check tire condition. Repair or replace. |
| Trailer is unstable or noisy during towing. | Tire pressure low | Check tire pressure and inflate as necessary. |
| Trailer is unstable or noisy during towing. | Wheel lug nuts loose | Torque wheel lug nuts. |
| Trailer is unstable or noisy during towing. | Tire/wheels mismatched on same axle | Check compatibility of wheels and tires on each end of axle. |
| Trailer is unstable or noisy during towing. | Trailer not level horizontally (side to side) | Check compatibility of wheels and tires of each axle. Check trailer weight distribution and cargo. |
| Trailer is unstable or noisy during towing. | Trailer not level horizontally (front to back) | Check and adjust trailer hitch height. |
| Trailer is unstable or noisy during towing. | Generator set not secured to trailer | Check mounting hardware. |
| Trailer is unstable or noisy during towing. | Trailer suspension noisy | Lubricate suspension contact points. |
| Trailer is unstable or noisy during towing. | Trailer suspension worn or damaged | Check components and replace as necessary. |
| Trailer is unstable or noisy during towing. | Tow vehicle suspension worn or damaged | Check tow vehicle suspension and replace as necessary. |
| Trailer is unstable or noisy during towing. | Trailer hitch worn or damaged or incorrectly attached | Reconnect trailer to tow vehicle. Replace worn or damaged components as necessary. |
| Trailer is unstable or noisy during towing. | Wheel bearings underlubricated | Disassemble, clean or replace, and repack. |
| Trailer is unstable or noisy during towing. | Axle shaft or spindle bent | Check components and replace as necessary. |
| Trailer is unstable or noisy during towing. | Bearings worn | Check components and replace as necessary. |
| Trailer is unstable or noisy during towing. | Trailer overloaded | Check trailer weight capacity and cargo. |
| Tow vehicle and trailer are unstable or noisy during braking | Tow vehicle brakes worn | Check brake fluid level. Add fluid as necessary. |
| Tow vehicle and trailer are unstable or noisy during braking | Brake components worn | Check component and replace as necessary. |
| Tow vehicle and trailer are unstable or noisy during braking | Brake linings/drums greasy or oily | Clean or replace. |
| Tow vehicle and trailer are unstable or noisy during braking | Rotors/drums out of round | Machine or replace. |
| Main circuit breaker(s) tripped or trips when reset | Circuit breaker overloaded | Reduce circuit load. Reset circuit breaker. |
| Main circuit breaker(s) tripped or trips when reset | Electrical circuit shorted | Check electrical circuit wiring and load connections. |
| Main circuit breaker(s) tripped or trips when reset | Circuit breaker inoperative | Contact an authorized service distributor/dealer or licensed electrician. |
| Duplex circuit breaker(s) tripped or trips when reset | Circuit breaker overloaded | Reduce circuit load. Reset duplex circuit breaker(s). |
| Duplex circuit breaker(s) tripped or trips when reset | Electrical circuit shorted | Check electrical circuit wiring and load connections. |
| Duplex circuit breaker(s) tripped or trips when reset | Circuit breaker inoperative | Contact an authorized service distributor/dealer or licensed electrician. |
| Duplex circuit breaker(s) tripped or trips when reset | GFCI outlet tripped | Check ground circuit of GFCI outlet. |
| Duplex receptacles have no power | Generator set not running | Power to duplex receptacles is from the generator set—not shore power. |
| Duplex receptacles have no power | Duplex circuit breaker(s) tripped | Reduce circuit load. Reset duplex circuit breaker(s). |
| Duplex receptacles have no power | Voltage selector switch is in the 480-volt position (high wye). (Voltage selector switch not used on all models) | Duplex receptacles are not functional when the voltage selector switch is in the 480 volt (high wye) position. The voltage selector switch must be in the single-phase or low wye position in order for the duplex receptacles to have power. |
| Voltage selector switch position does not match load voltage. | Unit not set up for application | Contact onsite electrician or rental distributor. See Section 3, Electrical Connections and Requirements, for more information. |
| Voltage selector switch knob does not rotate. | Padlock installed on lockout feature | Contact onsite electrician or rental distributor. |
| Voltage selector switch knob does not rotate. | Lockout button inoperative | Press lockout button and rotate (do not move the voltage selector switch while generator set is running). See Section 3, Electrical Connections and Requirements, for more information. |
| Voltage selector switch knob does not rotate. | Voltage selector switch inoperative (Voltage selector switch not used on all models) | Contact an authorized service distributor/dealer or licensed electrician. |
| User-supplied wiring between customer connection panel and load devices feels hot or has burning odor | Wiring undersized for application | Contact onsite electrician or rental distributor. |
| User-supplied wiring between customer connection panel and load devices feels hot or has burning odor | Terminal connections loose and/or corroded | Clean, if required, and tighten terminal connections. Torque customer connection panel load lugs to specifications. |
| Battery charger and/or block heater not functioning | Devices not connected to receptacle | Plug devices into respective receptacles |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Controller and Emergency Stop Switch; Controller circuit board(s) inoperative; Controller circuit board(s) wiring fault; Controller fault. See the table for the matching fixes.
Documented causes: Controller and Emergency Stop Switch; Controller circuit board(s) inoperative; Controller fault; Controller internal fuse blown. See the table for the matching fixes.
Documented causes: Tire(s) worn or damaged; Tire pressure low; Wheel lug nuts loose; Tire/wheels mismatched on same axle. See the table for the matching fixes.