Kohler Generator Fault Codes
What every fault message on a Kohler RDC2 or DC2 controller display means, in plain language — what usually causes it, what's safe to check yourself, and when it's a job for a technician.
How Kohler shows a fault
Kohler's residential and light-commercial standby line runs on an RDC2 or the simpler DC2 controller, and both display faults as plain English text right on the panel — "Over Crank," "Voltage High," "Low Coolant Level" — rather than a numeric code the way Generac does or a blink pattern the way Briggs & Stratton's Home Generator System does. That makes a Kohler fault easier to search for by name, but it also means the exact wording can vary slightly by controller generation and model, which is why every code page here states which Kohler line and controller it applies to.
Not every fault on this list stops the generator. Some, like Battery Voltage Low, are warnings that leave the unit running or armed in standby while flagging something worth fixing soon. Others, like Over Crank or EngineSpeed High, are full shutdowns that lock the controller out until someone clears the fault at the panel — typically by pressing OFF and then AUTO once the underlying problem is addressed. This page only covers Kohler's residential standby line, which is where a documented, verifiable fault-code list actually exists; smaller Kohler portable and job-site generators generally don't carry a controller with a fault-message display like this at all, so we haven't invented codes for them.
Every Kohler code on this site
| Code | Severity | Meaning |
|---|---|---|
| Battery Voltage Low | Medium | Starting-battery voltage under ~12.5 VDC for 90+ seconds while idle. |
| Over Crank | High | Three failed start attempts in a row. |
| Engine Oil Pressure Low | High | LOP switch detects low oil pressure for 5+ seconds. |
| High Engine Temperature | High | Coolant temp sensor/switch reports an overheat (liquid-cooled models). |
| Low Coolant Level | High | Expansion tank sensor detects coolant below minimum (liquid-cooled models). |
| EngineSpeed High | High | Engine speed over ~115% of normal for 0.3+ seconds — overspeed. |
| EngineSpeed Low | Medium | Engine speed under ~85% of normal for 3+ seconds — underspeed, often overload. |
| Voltage High | High | Output over ~120% of nominal voltage for 2+ seconds. |
| Voltage Low | Medium | Output under ~80% of nominal voltage for 10+ seconds. |
| M-N Invalid Shutdown Fault | Medium | Controller lost its stored engine model configuration. |
Start with what your generator is doing
No fault text visible, or unsure which message matches your symptom? These jump straight to the relevant troubleshooting page:
- Generator Won't Start
- Low Battery or Charger Fault
- Low Oil Pressure Shutdown
- Overspeed Shutdown
- Generator Runs Then Shuts Down
- Overload or Nuisance Tripping
Air-cooled vs. liquid-cooled models
Two of the ten codes here — High Engine Temperature and Low Coolant Level — only apply to Kohler's liquid-cooled RCA and RCL series, since they depend on a coolant sensor and a separate high-temperature switch that air-cooled models simply don't have. If you're working on a smaller air-cooled Kohler standby unit and neither of those messages will ever appear on your display, that's expected, not a sign something's missing from the controller.
What Kohler repairs typically cost
Broad U.S. ranges, not a Kohler price list — get a local written quote before paying anything. Starting-battery replacement, the single most common fix behind Battery Voltage Low and Over Crank faults, runs about $200–$500 installed. Most other standby generator repairs land in the $150–$600 range on top of a typical $75–$150 diagnostic fee. See the full cost breakdown on the home page, including where control-board and alternator repairs fall.
- Kohler's liquid-cooled RCA/RCL models run a pressurized coolant system — never open it while hot.
- Standby units carry mains-voltage output and, on LP/NG models, a live fuel-gas supply; fuel-line and transfer-switch work belongs with someone licensed to do it.
- Never run a generator, or work on one, inside a garage or enclosed space — carbon monoxide from the exhaust is fatal and has no smell.