In short. A generator alarm is the controller telling you what it detected — not always what is wrong. Some alarms are simple housekeeping you can clear yourself. Some can be reset once. And some — low oil pressure shutdown, high temperature shutdown, overspeed, short circuit, earth fault — must never be reset until a trained person has found the cause, because a second start can turn a small fault into a destroyed engine or a fire. This page sorts the common alarms into three colours so the person on site does the right thing at 2 a.m.
Who this page is for: For security staff, electricians, supervisors and facility managers who are first to the generator when it alarms: know what the message means, what you can safely check, and when a reset would make things worse.
Key facts
- Photograph before you press anything. Resetting can clear the evidence the engineer needs.
- A shutdown is the engine protecting itself. Restarting it repeatedly removes that protection.
- One of the commonest reasons a standby set does not start in a power cut is not a fault — it is the panel left in Off or Manual after a test, or an emergency stop left pressed.
- An alarm that returns after one reset is a pattern, not bad luck. Call for investigation; do not reset again.
The three kinds of message
| Type | What the set does | What it means for you |
|---|---|---|
| Warning (pre-alarm) | Keeps running; shows the message, often with a buzzer | Something is drifting towards a limit. You have time to act — reduce load, check airflow, arrange fuel. |
| Electrical trip | Opens the generator breaker; the engine usually runs on for a cool-down, then stops | The load or the wiring caused it. The engine is probably fine; the electrical system needs checking. |
| Shutdown | Stops the engine immediately | The controller decided running on would cause damage. Treat as serious until proven otherwise. |
Panel modes — check these first
- Auto: the normal standby position. The set starts on mains failure and stops after mains returns. A standby set should live here.
- Manual / Run: runs only when someone starts it. Fine for testing — but a set left in Manual will not start in a power cut.
- Off / Stop / Reset: will not run at all. Also the position used to reset alarms on many controllers.
- Test: on some panels, starts the set with or without load for a test run.
After every test, service or alarm reset, the last job is to return the panel to Auto and confirm the display shows no active alarms.
Before you reset: the five-step routine
Alarm guide
Alarm names differ slightly between controller makes, but the meanings are the same. If your display shows something not listed here, treat it as Amber.
| Alarm | What it means | What you can safely check | Action |
|---|---|---|---|
| Low oil pressure (warning) | Oil pressure is falling towards the shutdown level. | Unload the set if possible. When stopped and after a few minutes, check the oil level on the dipstick. | Amber — reset once; if it comes back, call |
| Low oil pressure (shutdown) | The engine was stopped to save it from bearing damage. | Check oil level and look for leaks under the set. Do not restart. | Red — do not reset, call |
| High coolant temperature (warning) | Engine running hot. | Check radiator air is not blocked; reduce load; check canopy doors and louvres are not obstructed. | Amber — reset once; if it comes back, call |
| High coolant temperature (shutdown) | Engine stopped to prevent overheating damage. | Let it cool. Never open the radiator cap hot. When cold, check coolant level and radiator fins. | Red — do not reset, call |
| Low coolant level | Coolant below the sensor in the header tank. | When cold, check level and look for leaks. | Red — do not reset, call |
| Overspeed | Engine ran above its safe speed — a serious event. | Do not restart. Note what load had just been removed. | Red — do not reset, call |
| Underspeed / under-frequency | Engine could not hold speed — usually overload or fuel starvation. | Check load just applied; check fuel level and day tank. | Amber — reset once; if it comes back, call |
| Fail to start | Engine did not fire within the set number of attempts. | Check fuel level, fuel valve open, emergency stop released, battery voltage on display. | Amber — reset once; if it comes back, call |
| Fail to stop | Engine kept running after a stop command. | Use the emergency stop. Do not leave the set unattended. | Red — do not reset, call |
| Emergency stop | An emergency stop button is pressed or its circuit is open. | Find out who pressed it and why. Release only when the reason is cleared. | Amber — reset once; if it comes back, call |
| Charge alternator failure | The engine’s battery-charging alternator is not charging — often a broken belt. | When stopped, look at the fan and alternator belt. | Amber — reset once; if it comes back, call |
| Low battery voltage | Starting battery or charger problem; next start may fail. | Check the battery charger is switched on and its indicator is normal. | Amber — reset once; if it comes back, call |
| High battery voltage | Charger over-charging; batteries can be damaged. | Note the reading and call. If the battery is hot, swelling or smells, switch off the charger at its supply and call immediately. | Amber — reset once; if it comes back, call |
| Low fuel level | Fuel below the alarm level. | Arrange refuelling; check the level against the log in case of loss. | Green — fix and reset |
| Fuel level sensor fault | The controller cannot read the fuel level. | Dip the tank to confirm actual level. | Amber — reset once; if it comes back, call |
| Generator over-voltage | Output voltage too high — protects connected equipment. | Note the load: light load with capacitor banks or UPS filters is a common cause. | Red — do not reset, call |
| Generator under-voltage | Output voltage too low. | Note the load just applied; check for a large motor start. | Amber — reset once; if it comes back, call |
| Over-current / overload | Load more than the set should carry. | Reduce load before restarting; note which loads were running. | Amber — reset once; if it comes back, call |
| Short circuit | Very high current — a fault in cables or equipment. | Do not reset or close the breaker again. Keep people away from the switchboard. | Red — do not reset, call |
| Earth fault | Current leaking to earth somewhere on the system. | Do not reset. Note which circuits were on. | Red — do not reset, call |
| Reverse power | On paralleled sets: one set is being driven as a motor. | Note which set tripped and its fuel level. | Red — do not reset, call |
| Phase sequence wrong | Phases connected in the wrong order — usually after cable work. | Do not connect load. Motors would run backwards. | Red — do not reset, call |
| Unbalanced load | One phase carrying much more than the others. | Note single-phase loads; inform the electrician. | Amber — reset once; if it comes back, call |
| Loss of speed signal / sensor open circuit | The controller lost a sensor reading, usually wiring or the sensor itself. | Do not touch engine wiring. Note the message and call. | Amber — reset once; if it comes back, call |
| Engine electronics communication fault | Controller lost contact with the engine’s electronic control unit. | Note the code shown; switch nothing off at the battery. | Red — do not reset, call |
| Aftertreatment / exhaust-system alarm | On newer low-emission sets: exhaust after-treatment needs attention (for example a regeneration request or reagent level). | Read the exact message; check reagent level if your set uses one. | Amber — reset once; if it comes back, call |
| Breaker failed to close / open | Changeover did not complete. | Check the panel for a tripped breaker; do not force it. | Red — do not reset, call |
| Maintenance due | Service timer has run out. | Book the service; the set will still run. | Green — fix and reset |
| Mains failure / mains return | Information only: the AMF panel saw mains go or come back. | No action unless the set did not respond. | Green — fix and reset |
The panel-door card
Print this, laminate it and fix it inside the generator room door or on the canopy, next to the controller.
Generator alarm — what to do
First: photograph the screen. Note the time and what was running.
RED — do not reset. Call immediately: Low oil pressure (shutdown), High coolant temperature (shutdown), Low coolant level, Overspeed, Fail to stop, Generator over-voltage, Short circuit, Earth fault, Reverse power, Phase sequence wrong, Engine electronics communication fault, Breaker failed to close / open.
AMBER — check, reset once. If it comes back, call: Low oil pressure (warning), High coolant temperature (warning), Underspeed / under-frequency, Fail to start, Emergency stop, Charge alternator failure, Low battery voltage, High battery voltage, Fuel level sensor fault, Generator under-voltage, Over-current / overload, Unbalanced load, Loss of speed signal / sensor open circuit, Aftertreatment / exhaust-system alarm.
GREEN — fix and reset: Low fuel level, Maintenance due, Mains failure / mains return.
After any reset: panel back to AUTO; no alarms on the screen.
Same alarm back after one reset = call, do not reset again.
Service contact: ____________________ Site in-charge: ____________________
Worked examples (illustrative)
Fail to start in the evening
Illustrative case. Mains fails at 9 p.m. in an apartment complex. The display shows “Fail to start”. The guard resets and presses start five more times; the battery goes flat and now nothing happens at all.
What should have happened: Fail to start is Amber. Photograph, then check the four simple things — fuel level, fuel valve, emergency stop, battery voltage on the display. Here the fuel valve had been left closed after a filter change that afternoon. Opening it and resetting once would have started the set, after the fuel system was bled if the technician’s instructions required it. Five extra attempts flattened the battery and turned a 2-minute problem into a 2-hour one.
High temperature shutdown on a May afternoon
Illustrative case. At 3 p.m., with the outside temperature over 42 °C, a factory set shuts down on high coolant temperature. The supervisor wants it back on immediately because production has stopped.
What should happen: this is Red. The engine must cool; opening the radiator cap now could scald someone. On inspection, cardboard packaging had been stacked against the canopy’s air inlet louvres. Clearing it is the first step, but a technician still needs to check coolant level, radiator condition and whether the engine was damaged before the set returns to load.
Over-voltage trip at night
Illustrative case. A plant’s set trips on over-voltage only at night when the load is light. This is Red because it points to something on the system — commonly the capacitor bank or UPS filters pushing the generator into a leading power factor. The fix belongs to an electrician, not a reset button.
Alarm log
| Date & time | Alarm shown | Load running | What was checked | Reset? (once) | Called / outcome |
|---|---|---|---|---|---|
Ten-minute monthly drill
- Show each new guard or operator where the controller, emergency stop and fire extinguisher are.
- Walk through the panel modes and confirm the set is in Auto.
- Read the door card together; ask them to tell you which colour “Low oil pressure shutdown” is.
- Show how to photograph the display and where the alarm log is kept.
- Confirm the service contact number on the card is current.
For managers: make the alarm guide work
- Remote alarms: if the set is far from where people sit, a remote alarm panel or a phone alert means a warning is seen before it becomes a shutdown.
- Event logs: controllers keep a log of alarms with time and readings. Ask your service provider to download it at each service and review repeats.
- Do not let settings be changed to “stop nuisance alarms”. A recurring alarm is a symptom; raising the limit hides it until something fails.
- Keep the card current after any controller replacement — alarm names can change.
Common mistakes
- Resetting before photographing the display and event log.
- Resetting a shutdown alarm repeatedly instead of calling.
- Leaving the panel in Off or Manual after a test or service.
- Raising alarm limits to stop ‘nuisance’ alarms instead of finding the cause.
What to send us
Send a photograph of the controller display and any alarm pages, the time it happened, what load was running, what was checked on site, and the set’s kVA and controller make if known. Use the service and AMC enquiry, or WhatsApp the details and photographs.
Questions site teams ask
Can I reset a generator alarm myself?
For some alarms, yes — low fuel, maintenance due and mains failure messages are housekeeping. Many warnings can be reset once after a simple check. Shutdowns such as low oil pressure, high temperature, overspeed, short circuit and earth fault should never be reset until a trained person has found the cause.
Why did the generator not start in the power cut when there was no alarm?
One of the most common reasons is that the panel was left in Off or Manual after a test or service, or an emergency stop was left pressed. Always return the panel to Auto after any work.
What is the difference between a warning and a shutdown?
A warning means a value is drifting towards a limit and the set keeps running. A shutdown means the controller stopped the engine to prevent damage.
Why should I photograph the screen before resetting?
Resetting can clear the alarm details and push older events out of the log. A photograph gives the engineer the exact message, readings and time.
The same alarm keeps coming back. What should we do?
If an alarm returns after one reset, treat it as a fault to investigate, not an alarm to reset again. Call your service provider with the photographs and the alarm log.
Can a guard start the generator manually in a power cut?
Only if trained and authorised, and only if there is no Red alarm active. Follow the site’s written procedure.
Related pages
- Controller Diagnostics (technician-level)
- Generator Troubleshooting
- Generator Maintenance Planning
- Protection Alarms, Events & Disturbance Records
- Generator Fuel Theft, Security and Refuelling Control
- Breakdown Diagnostics
- Generator Not Starting? A Step-by-Step Diagnosis for DG Sets
- Generator Overheating and High Coolant Temperature Shutdowns
- Low Oil Pressure Shutdown on a Generator
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer. Last updated 3 November 2026.