First: Read the Controller

Before touching anything, look at the generator's control panel. On Generac units — the most common brand in Hays County — the status light tells the story: green means ready, yellow means maintenance is due, and red means a fault has shut the unit down. If there's a fault, the display shows a message or code. Write down exactly what it says before you reset anything — that wording is the first thing a technician will ask for, and it points at the system that failed.

The Checklist, in Order

1. Is the unit actually in AUTO?

A generator left in OFF after service — or switched off during yard work and never switched back — will sit silent through an outage. Check the control switch position first. If a fault is latched, Generac's manuals describe the standard reset: switch to OFF, wait about 30 seconds, then back to AUTO. If the fault returns immediately, stop resetting it — a fault that comes straight back is a real problem, not a nuisance.

2. The battery — the most common cause

More failed starts trace to the starting battery than to any other single part. The battery cranks the engine; if it's weak, you get slow cranking, clicking, or silence, and the controller may show a low-battery or charger warning. Homeowner-safe checks:

Look at the connections. Corroded, loose, or green-crusted terminals are a classic cause. If a terminal is swollen, leaking, or damaged, don't handle it — that's a technician or dealer job.
Check the age. Standby batteries commonly last about three to five years. A battery older than that is guilty until proven innocent. Most Generac air-cooled units spec a Group 26R battery, 540 CCA minimum (per Generac's specification sheet) — match the spec if a dealer replaces it.
Ask whether it missed its exercise. If the unit also failed to run its weekly exercise, the battery or charger is the prime suspect — the exercise exists precisely to catch this before an outage does.

3. Fuel supply

An engine that cranks energetically but never fires — or fires and dies — is usually starving. The controller fault for this is typically Overcrank: it cranked through its whole start cycle without starting.

Propane: Read the tank gauge. A low tank is a double problem in cold weather, when a nearly empty tank can't vaporize fuel fast enough to feed the engine. If the gauge is low, a fuel delivery may be the whole fix.
Natural gas: Confirm the shutoff valve at the generator is open, and check whether your other gas appliances (furnace, water heater, stove) are working. If the whole gas service is down, that's the utility's problem, not the generator's.
Hands off the plumbing. Regulators, fuel lines, and pressure adjustments are technician and gas-utility territory. If you smell gas, don't touch switches or the unit — leave the area and call your gas utility or 911.

4. Oil level

Standby engines protect themselves: if oil pressure doesn't come up, the unit shuts down (or won't start) rather than destroy itself. Wait a few minutes after cranking, then check the dipstick. If the level is below the Full mark, top it up with the oil your manual specifies. A low-oil fault that repeats with a full sump is a technician call.

5. Air in, exhaust out

Generators breathe through louvers and reject heat through the enclosure. Shrubs grown into the unit, wasp nests, leaves, ice, or a fence built too close can cause high-temperature shutdowns and rough running. Clear the area back to the clearances on our cost guide's placement section — 3 feet at the front and ends, 18 inches at the rear, 5 feet overhead — and check that nothing blocks the exhaust.

What the Fault Message Means

Exact wording and codes vary by controller generation, but the common Generac fault names point in consistent directions:

Fault	What it means	First move
Overcrank	Cranked through its start cycle without firing	Fuel supply and battery, above
Low Battery	Battery voltage low or charger not keeping up	Battery age and connections
Low Oil Pressure	Oil pressure didn't come up on start	Check the dipstick; technician if full
RPM Sense Loss	The engine ran (or tried to) but the controller lost its signal	Technician diagnosis
Overspeed / Underspeed	Engine speed out of range — governor or fuel delivery	Technician diagnosis
High Temperature	The unit overheated or thinks it did	Clear airflow blockages; technician if clear
Undervoltage / Overvoltage	The generator side isn't producing correct power	Technician diagnosis

It Runs — but the House Has No Power

That's a different failure, and it isn't the engine. Check the generator's own main circuit breaker (mounted on the unit): if it tripped, resetting it is a normal homeowner check. If the breaker is fine and the house is still dark, the automatic transfer switch didn't transfer — that's inside-the-switch work for an electrician or dealer technician, not a DIY diagnosis.

Where homeowner checks end: anything involving fuel lines or regulators, anything inside the enclosure beyond battery, oil, and air-filter basics, electrical work in the transfer switch, and any fault that returns right after one reset. One more rule: never bypass a safety shutdown to "get through the night." The shutdown is protecting the engine — or you.

If This Keeps Happening

A single no-start after years of service is usually a battery. A pattern — missed exercises, repeated faults, a unit that's aging out — is the point where owners start pricing replacement, because the failure always seems to pick the worst outage. If that's where you are, a replacement quote is free, and current models report exercise failures and battery problems to your phone before an outage finds them. Not sure what size you'd need? Run the sizing calculator first.

Troubleshooting steps follow the fault, battery, and maintenance guidance in Generac owner's manuals and Generac Support's published help articles. Battery specification: Generac Guardian Series specification sheet (Group 26R, 540 CCA minimum). Your model's manual is the authority for your unit.

Last updated: October 2026.

Why Won't My Standby Generator Start?