Generator Won't Start
The engine either doesn't crank at all, cranks but never catches, or catches for a second and dies. All three are different problems with different fixes, and on most standby units the controller will name the actual cause once it's tried and failed — the trick is knowing where to look.
What this looks like
"Won't start" usually shows up one of three ways, and telling them apart matters before you touch anything. First, dead silence: the transfer switch calls for a start (or you press the manual button) and nothing happens — no cranking sound at all. That points at the control circuit or a battery too weak to even engage the starter solenoid. Second, it cranks — you hear the starter turning the engine over, sometimes for the controller's full attempt sequence — but the engine never actually fires. On a Generac Evolution or Nexus panel this ends in an Overcrank alarm; Kohler's RDC2/DC2 shows Over Crank as plain text after three failed attempts; Briggs & Stratton's Home Generator System has no display, so it reports the same outcome as four blinks of its single LED, decoded as FC_4. Third, the engine catches and runs briefly, then quits — that's a separate problem covered on the generator runs then shuts down page, since it usually means a sensor or protective shutdown, not a starting failure.
Most likely causes, ranked
- No usable fuel reaching the engine. A closed LP valve, an empty propane tank, a natural-gas supply that got shut off during other work, or gasoline that's gone stale after sitting for months. This is the single most common reason a generator won't start and the fastest to rule out.
- Starting battery too weak to crank. Standby generator batteries live outdoors, get cycled by weekly exercise runs, and typically last 2–4 years. A battery that reads fine on a voltmeter can still lack the cranking amps to turn the engine over under load.
- Fouled or worn spark plug, or an ignition fault. Gasoline portables and some standby models are the usual suspects — a plug that's wet from a flooded attempt or caked with carbon won't fire reliably.
- Lost crank/RPM signal. On Generac units the controller can crank the engine fine but never detect that it's actually running, which shows up as a 1501/1505/1511/1515-series sensor-loss fault rather than a plain overcrank.
- Clogged fuel filter, fuel-pressure regulator, or carburetor. More likely if the unit ran fine as recently as its last exercise cycle and has gradually gotten harder to start since.
Which fault codes match this
| Brand | Code / display | What it confirms |
|---|---|---|
| Generac | 1100 (Overcrank) | Full crank sequence attempted, engine never caught |
| Generac | Low Battery | Battery voltage too low for a reliable next crank |
| Generac | 1501 / 1505 / 1511 / 1515 | No RPM/timing signal detected while cranking |
| Kohler | Over Crank | Three unsuccessful start attempts, then lockout |
| Kohler | Battery Voltage Low | Battery below ~12.5V while the engine is off |
| Briggs & Stratton | FC_4 (4 blinks) | Engine failed to start after repeated attempts |
| Briggs & Stratton | FC_1 (1 blink) | Battery output too low to crank the engine |
What you can check yourself
- Read the display or count the LED blinks before doing anything else — that alone tells you whether this is a fuel/ignition problem or a battery problem, and links to the exact page above.
- Confirm the fuel valve is fully open and there's actually LP, natural gas, or fresh gasoline getting to the engine — closed valves after landscaping or other yard work are a frequent, embarrassing cause.
- Test the starting battery at rest with a multimeter; a healthy 12V battery reads about 12.4–12.7V, and clean any visible corrosion on the terminals.
- Clear the fault at the controller (OFF, wait a few seconds, then AUTO) before attempting a manual restart, so you're not fighting a stale lockout.
- On gasoline units, pull the spark plug and check whether it's fouled, wet, or caked — a wet plug after a failed start usually means a flooded cylinder, not an ignition failure.
- Note whether the engine cranks strongly or weakly — strong-but-no-catch points to fuel or ignition, weak cranking points straight back to the battery.
More help
Already have the exact code or blink count? Use the code lookup to jump straight to its page. Otherwise, check the full list for your brand: Generac, Kohler, or Briggs & Stratton.