Last verified: October 1, 2026
When a Generac standby generator detects a problem, it shows an alarm on the controller (and in the app on connected models) and usually shuts down to protect itself. Some alarms you can safely deal with yourself, such as Low Oil Pressure, Overload or Overcrank caused by a closed fuel valve. Others, such as Overspeed or Overvoltage, need a dealer. This guide lists the alarms in Generac’s owner’s manual for its 9–22 kW air-cooled generators, what they mean and what to do.
Alarm messages and what to do
| Alarm | What it means | What the manual says to do | DIY or dealer? |
|---|---|---|---|
| Low Battery | Battery charge is too low | Check the battery through the battery menu; replace it if the controller says to | Usually dealer for replacement |
| Battery Problem | The controller has detected a battery defect | Contact a dealer | Dealer |
| Overcrank | The engine cranked several times but didn’t start | Make sure the fuel shut-off valve is on; clear the alarm; try again | DIY first, then dealer |
| Low Oil Pressure | Not enough oil pressure | Check the oil and fill to the Full mark | DIY (engine off) |
| High Temperature | Engine is overheating | Check ventilation; remove anything blocking the intake or exhaust | DIY first, then dealer |
| Overload | Household load is more than the generator can supply | Turn off some household loads; return the controller to Auto | DIY |
| RPM Sensor Loss | The engine speed signal was lost | Clear the alarm, remove loads and restart; call a dealer if it repeats | DIY once, then dealer |
| Overspeed | Engine running too fast | Contact a dealer | Dealer |
| Underspeed | Engine running too slowly | Contact a dealer | Dealer |
| Overvoltage | Output voltage too high | Contact a dealer | Dealer |
| Undervoltage | Output voltage too low | Contact a dealer | Dealer |
| Fuse Problem | The control panel’s 7.5 A fuse may be blown | Check the fuse; if blown, replace it with an ATO 7.5 A fuse; if intact, contact a dealer | DIY first, then dealer |
| Low Volts Remove Load | Voltage dropped, usually from too much load | Clear the alarm, remove household loads, return to Auto | DIY |
| Not Activated | The unit was never activated after installation | Activation is described in the installation manual; ask your installer | Installer |
| Service A / Service B | Scheduled maintenance is due | Have the service done; the reminder is cleared afterwards | Dealer or DIY maintenance |
Source: alarm table in the Generac owner’s manual for 60 Hz air-cooled generators, 9–22 kW. “Dealer” means an Independent Authorized Service Dealer (IASD).
What about numeric error codes?
Newer Generac controllers can show a numeric code along with the alarm name. The numbers are specific to the controller and model, so look them up in the manual for your unit or in the Generac app rather than relying on generic lists online. The alarm name tells you which category the problem is in, which is what you need to decide between a quick check and a dealer call.
How to clear an alarm
Generac’s quick reference guide says to clear an active alarm by pressing OFF, then ENTER, then AUTO. If the alarm comes back, contact a dealer. Other controllers may differ, so check your manual. If the same alarm comes back, don’t keep resetting it: repeated alarms usually mean a real fault that a technician should diagnose.
Warnings vs alarms
Many controllers distinguish between a warning (the generator keeps running or stays ready, but something needs attention soon, like maintenance due) and an alarm (the generator shuts down or won’t start). A maintenance reminder doesn’t mean the generator is broken, but don’t ignore it before storm season.
Reading the status lights
Generac’s quick reference guide pairs each alarm with a colored LED:
| Light | What it means | Examples |
|---|---|---|
| Green | Unit ready or running normally | Normal operation; a start-up delay countdown |
| Yellow | Warning: something needs attention, but the unit may still run | Low Battery, Battery Problem, Charger Warning, Service A, Service B, Inspect Battery |
| Red | Alarm: the unit has shut down or won’t start | High Temperature, Overload, Low Oil Pressure, Overcrank, Overspeed, Undervoltage, Fuse Problem |
A yellow light is a reminder to act soon; a red light means the generator isn’t protecting your home right now.
What to do in the middle of an outage
- Read the alarm name on the controller (or in the app).
- If it’s one you can safely handle (Overload, Low Oil Pressure, Overcrank from a closed valve, High Temperature from blocked vents), fix the cause first.
- Clear the alarm as the manual says (OFF, ENTER, AUTO on Generac controllers).
- If it comes back, stop resetting it and call the dealer. Repeated resets can hide a real fault.
- Meanwhile, protect what matters most: keep the fridge closed, use a battery backup for medical devices, and avoid opening the generator’s electrical compartments.
Frequently asked questions
Can I ignore a yellow warning light?
Not for long. Yellow warnings such as Low Battery or Service A/B mean the generator still works for now, but the issue can turn into a no-start. Deal with it before the next storm.
Where do I find the meaning of a numeric code?
In the owner’s manual for your exact model or in the manufacturer’s app. Numbers vary between controller generations, so avoid generic lists.
Will clearing an alarm erase the history?
Controllers generally keep an event log that a dealer can read, even after you clear the active alarm. Note the alarm name and time anyway; it helps the technician.
The four alarms that most often have simple fixes
- Overcrank: most often a closed fuel valve after service, or an empty propane tank.
- Low Oil Pressure: oil level dropped, common during long outages. Check and top up with the engine off and cooled.
- Overload: too many big appliances at once. Stagger the dryer, oven and water heater, or consider load management.
- High Temperature: leaves, snow or plants blocking the vents.
If the generator won’t start at all, follow our step-by-step guide: Generac generator won’t start.