A generator PM is not one task. It is a tour through several independent systems, each of which can leave you dead in an outage on its own: the engine, the fuel system, the starting batteries, the automatic transfer switch, cooling and ventilation, controls and alarms, the exhaust, and the general condition of the set and its enclosure. Skip one and you have not done a PM — you have done a partial inspection and signed it like a full one.
This guide walks every system in the order a technician actually works them, with the checks and readings that belong on each. At the end it covers the part most checklists ignore: making the completed checklist mean something.
Why the record matters
Engine
The engine is where most consumable maintenance lives. Work it cold or per the manufacturer's guidance, and check:
- Oil level and condition; oil and filter change on the manufacturer's interval
- Coolant level, condition, and concentration; radiator, hoses, and clamps for leaks or rot
- Air filter condition and the restriction indicator
- Belts and pulleys for wear, glazing, and tension
- Any visible oil, coolant, or fuel leaks at the engine and accessories
- Governor and throttle linkage, where applicable, for free and correct movement
Fuel system
Fuel problems are quiet until the engine needs to run for a sustained period — exactly when you cannot afford a problem. Check:
- Fuel level and any transfer hardware (day tank, transfer pumps, float controls)
- Fuel filters and water separators
- Lines and fittings for leaks, chafing, and secure mounting
- Fuel quality
- Tank, venting, and spill containment — confirm against the requirements your AHJ enforces
Diesel deserves special attention. Diesel fuel ages, and it is subject to water intrusion and microbial growth — any of which can clog fuel filters and starve the engine when it finally has to carry load. A standby tank that sits full for months is the worst case: long dwell time, condensation, and a fuel sample nobody has looked at.
[SME-1: diesel fuel program] State whether your company runs a fuel-quality or fuel-polishing program on diesel sites, and how often fuel is sampled or treated — this is operator-specific and should not be invented.
For natural gas and LP sets the fuel checks shift but do not disappear. Confirm regulator condition, supply pressure, and that the supply valve is in the correct position.
Starting batteries
Start here if you only have time for one thing. The most common reason a standby generator fails to start is the starting battery. The engine can be perfect; if the battery cannot crank it, none of the rest matters. Check:
- Terminals for corrosion, cleanliness, and tightness
- Battery condition and a state-of-charge test
- Electrolyte level and specific gravity on serviceable (non-sealed) batteries
- Charger output and float voltage
- Cables and hold-downs for wear, security, and damage
- Install date and age — batteries have a finite service life, so track it
Track the age
Automatic transfer switch (ATS)
The ATS is the part of the system that decides whether the load is actually picked up by the generator when utility power is lost — and that re-transfers to normal power when it returns. A healthy engine sitting next to a switch that will not transfer is still a failed standby system. PM here includes:
- Visual inspection of contacts and connections
- Controller settings and time delays
- A transfer test: verify pickup on a simulated utility failure, and a clean re-transfer when normal power returns
Keep the two tests distinct in your head and on the record. A transfer testverifies the switching logic. A load test verifies the engine and alternator can carry load. Passing one does not prove the other.
Load testing
A transfer test moves the load; a load test proves the set can carry it. Load testing can use the building load or a load bank, and it should capture the real numbers under load: voltage, frequency, current, oil pressure, coolant temperature, and exhaust observations.
Light-load running is its own hazard on diesel sets. Run a diesel under-loaded for too long and you get wet-stacking — unburned fuel and carbon build up because the engine never reaches sufficient operating temperature. That is the practical reason load matters, not just a box to tick.
Don't invent the numbers
[SME-2: load testing capability] State whether your company's standard PM includes a load bank test step, and at what cadence you offer it — this is a capability and contract question only the operator can answer.
Cooling and ventilation
A generator that cannot reject its heat will derate or shut down under exactly the sustained run it exists for. Check:
- Radiator core, fins, and airflow path
- Fan and shroud condition
- Block heater operation and thermostat
- Ventilation louvers and dampers for free movement
The block heater earns its check because a cold engine is a slow-starting engine. Keeping the block warm shortens crank time and reduces wear on the first start — the start that has to work.
Controls and alarms
The control panel is how the system tells you it is ready — and how it tells the rest of the building when it is not. Check:
- Panel readings and that the set is in AUTO
- Alarm and event history review
- Safety shutdowns and alarm signaling, tested per the manufacturer's guidance
- Remote annunciation and monitoring, where present, reporting correctly
A set left in OFF or MANUAL after service will not start on its own in an outage. Confirming AUTO is not a formality — it is the most common way a serviced generator silently stops being a standby generator.
Exhaust
Exhaust is a safety system as much as a performance one. Check:
- Leaks anywhere along the run
- Supports and insulation
- Rain cap or flapper operation
- Condensate drains cleared
- Termination routed away from air intakes and occupied space
General inspection
The walk-around catches what the system-specific checks miss. Confirm:
- Enclosure, mounting, and vibration isolators
- Grounding
- Signage and housekeeping
- Access — can a tech and the next inspector actually get to the set?
- AUTO confirmed, with a correct exercise schedule set
How often to do all this
Service cadence is not a single number you pick. It is governed by the standard, the manufacturer's schedule, and the AHJ together. In broad terms operators run a frequent inspection, periodic operational and load testing, and a comprehensive annual service — but the actual intervals, load levels, and durations come from the governing standard, the manufacturer, and the AHJ for the specific site. Do not import a number from another facility's contract.
Make the checklist mean something
A PM is only as good as the record it leaves. This is the part that separates a clipboard from a defensible compliance trail, and it is where software earns its place.
Equipment details — make, model, serial, KW rating, fuel type, ATS — and the prior visit's readings can carry forward automatically rather than being retyped every visit. The tech walks up with the equipment list and last cycle's numbers already in front of them, and spends the visit capturing results, not transcribing nameplate data.
Then each result is tied to a named, authenticated person at a specific moment, in a record that cannot be quietly edited afterward. That is what makes it hold up. Your customers — hospitals, data centers, municipalities — carry their own compliance and audit requirements, and the maintenance record you produce is what supports them. A backfilled checkbox does not.
The litmus test
This guide pairs with a downloadable version of the checklist you can carry into the field and work from system by system.