Kohler Generator Error Codes
Kohler industrial and residential generators (SDMO, 5E, 20RES, and R-Series) use Decision-Maker controllers on larger models and APM (Advanced Power Management) controllers on newer residential units. Faults display as error numbers on the LCD or flash patterns on the status LED.
Kohler Decision-Maker Error Codes
| Error Code | Fault Description | Common Cause | Action |
|---|---|---|---|
| 1 | Low oil pressure | Oil pressure below 8 PSI | Check oil level, pressure switch, wiring |
| 2 | High engine temperature | Coolant temperature exceeds limit | Check coolant level, radiator, fan belt |
| 3 | Overspeed | Engine RPM exceeds 110% of rated | Test governor actuator, fuel supply |
| 4 | Underspeed | Engine RPM below 90% of rated | Check load, fuel pressure, air filter |
| 5 | Overcrank | Failed to start after programmed attempts | Check fuel, spark, battery, starter |
| 6 | Overvoltage | Output voltage exceeds 110% of rated | Test AVR, voltage adjustment pot |
| 7 | Undervoltage | Output voltage below 90% of rated | Test AVR, check load, identify motor start |
| 8 | Low battery | Battery voltage below 11.5V at rest | Charge or replace battery, test charger |
| 9 | Overload | Generator output exceeds rated capacity | Reduce load, check for short circuit |
| 10 | Cranking fault | Starter not engaging | Test starter solenoid, battery cables |
| 12 | Frequency fault | Output frequency outside range | Test governor, check fuel supply |
| 13 | Voltage regulator fault | AVR not producing output | Test AVR fuse, field voltage, rotor |
| 14 | Field overexcitation | Too much voltage to rotor field | Test AVR adjustment, regulator module |
| 15 | Loss of speed signal | RPM sensor signal lost | Check magnetic pickup, wiring, gap |
| 17 | Battery charger fault | Charger not functioning | Test charger output voltage |
| 18 | Fuel solenoid circuit | Solenoid open or short | Test solenoid coil resistance |
| 19 | Auxiliary shutdown | External shutdown signal | Check remote shutdown wiring, contacts |
| 20 | Emergency stop active | E-Stop button pressed | Reset E-Stop, check circuit |
| 22 | High exhaust temperature | Exhaust system restriction | Check exhaust piping, muffler, insulation |
| 23 | Magneto fault (gas models) | No spark detected | Test ignition module, kill wire |
| 24 | Camshaft sensor fault | No cam position signal | Test cam sensor, wiring, timing |
| 27 | Low oil pressure (pre-start) | Oil pressure low before start | Check oil level, switch stuck open |
| 34 | Actuator / governor fault | Throttle actuator not responding | Test actuator, linkage, controller output |
| 36 | Low coolant level | Coolant below sensor | Add coolant, check for leaks |
| 44 | Transfer switch communication fail | ATS not communicating | Check ATS controller, wiring harness |
Kohler APM 2-Button Controller (Residential)
Newer Kohler residential generators (5E, 20RES series) use a simple 2-button APM controller with indicator LEDs:
| LED Pattern | Meaning | Action |
|---|---|---|
| Red LED solid | Fault / shutdown | Read code on LCD |
| Red LED flashing | Warning (not shut down) | Check LCD for message |
| Green LED solid | Ready / standby | Normal |
| Green LED flashing | Unit running | Normal operation |
| Yellow LED solid | Exercise in progress | Normal |
| Yellow LED flashing | Service due | Schedule maintenance |
Most Common Kohler Faults
Error 5 — Overcrank
Same root causes as Generac 1200. On Kohler units, the most common sequence is: battery weak → slow crank → poor compression seal → no fire → overcrank. Start with a load test on the battery. Kohler uses Group 24 batteries on most residential units. Replace if resting voltage < 12.4V or if voltage drops below 10V under crank.
Error 3 — Overspeed
Kohler Overspeed typically triggers at 110% of rated RPM (1980 RPM on 1800 RPM generators, or 3960 on 3600 RPM models). Common cause on gas generators: the demand regulator diaphragm cracks, allowing too much fuel at deceleration. On newer units, check the electronic governor actuator for binding linkage. A failing actuator will show erratic hunting before the overspeed event.
Error 13 — Voltage Regulator Fault
The Kohler voltage regulator (AVR) supplies DC excitation to the rotor. If the regulator fails, the generator runs but produces no voltage. Quick test: engine running, measure DC voltage across the rotor brushes — should be 5–40 VDC depending on load. Zero volts = AVR not exciting the rotor. Common Kohler AVR part numbers: GM71908 (5–50 kW) and GM72405 (60–200 kW).
Parts Reference
| Part | Approx Cost | Notes |
|---|---|---|
| AVR (residential) Kohler | $120–$250 | GM71908 for 5E/20RES |
| AVR (industrial) Kohler | $250–$600 | GM72405-series |
| Battery charger board | $80–$150 | GM69463 |
| Magnetic pickup sensor | $30–$50 | Kohler A-467300 |
| Governor actuator | $150–$400 | Kohler A-435316 |
| Fuel solenoid (NG/LP) | $50–$100 | Kohler A-256914-S |
Need Replacement Parts?
Finding the right replacement parts for your equipment is critical to getting it running again. Check current prices on Amazon — prices and availability change frequently.
Transfer Switch Notes
Kohler uses KMC (Kohler Modular Controller) transfer switches. Common ATS faults: RXT controllers that lose programming after a firmware glitch, and GFI-neutral bonding issues that cause nuisance trips on newer RXT models. If the generator runs but the house doesn’t transfer, the ATS controller likely needs reprogramming.