Generator brands · Complete sets and engines
Repairs and Servicing for Cummins Generators and Engines
We repair and service Cummins generators on site across Gauteng: Cummins-built sets with PowerCommand controls, and other builders’ sets that run on a Cummins engine. The work covers the engine and fuel system, the alternator, the controller and the changeover. A photo of the set nameplate and the engine data plate tells us what to expect before we arrive.
Established 2006
20 years of experience
24/7 operations
We Arrive Within 1–2 Hours
(usually within 1 hour)
Free callouts and quotations
One-year warranty
Qualified and certified technicians
We Service & Repair All Generator Brands
All generator makes and models
1 kVA–20,000 kVA capability
A Cummins set, or a set with a Cummins engine
Cummins makes engines and also builds complete generator sets. A Cummins-built set pairs its own engine with, on most models, a PowerCommand controller (some smaller sets have a simpler panel) and often a Stamford alternator. Other builders fit a Cummins engine with their own alternator and controller, often a Deep Sea or ComAp module, so we check what is fitted.
Older sets may carry the Onan or Cummins Onan name, from the American generator maker that became part of Cummins. Many imported sets use engines from Cummins’ joint ventures in China, marked Dongfeng Cummins or Chongqing Cummins. They follow the same engine families, but parts are matched to their own data plate.
Cummins engine families and the sets they power
| Engine family | Rough set size | Fuel system | What it means on site |
|---|---|---|---|
| B series (4B, 6B) and QSB | Rough set sizeUp to about 200 kVA | Fuel systemMechanical pump on older B engines; electronic on the QSB | What it means on siteLift pump, injection pump and injectors decide how it starts and holds speed |
| C series (6C) and QSL | Rough set sizeRoughly 150–330 kVA | Fuel systemMechanical on the 6C; electronic on the QSL | What it means on siteTurbocharger and injector condition decide how cleanly it takes a block load |
| N series (NT855) and QSX15 | Rough set sizeRoughly 250–550 kVA | Fuel systemPT on the N series; electronic on the QSX15 | What it means on siteTwo different fuel systems in one size class, so the data plate decides the diagnosis |
| K series (KTA19, KTA38, KTA50) and QSK | Rough set sizeAbout 500 kVA into the megawatt range | Fuel systemPT on the K series; electronic on the QSK | What it means on siteLarge cooling systems, several turbochargers and many filters |
How the fuel system changes the diagnosis
The N and K series use Cummins’ own PT (pressure-time) fuel system. A PT pump supplies fuel at a controlled pressure, and camshaft-driven injectors meter each charge by how long their metering orifice stays open. Wear shows as hard starting, smoke, low power or hunting, and an out-of-specification pump is calibrated or exchanged, not adjusted by ear.
The QS series is electronic. Its engine control module (ECM) manages fuelling and engine protection and, on a Cummins-built set, passes its fault codes to the PowerCommand controller. A failed sensor or chafed harness can stop the engine with only a brief engine alarm showing, so we check the engine fault codes alongside the controller’s own alarm history, then test the circuit they point to. Older B and C engines with mechanical pumps are more tolerant of fuel quality, but must be bled of air after a filter change or a run until empty; see fuel system repairs.
Faults to watch for
What usually stops a Cummins set
Derates and ECM shutdowns: Shutting down or tripping
On QS engines a coolant-temperature, oil-pressure or speed-sensor fault can cut power or stop the engine. The engine fault code shown on the controller points to the circuit to test.
Low oil pressure alarms: Low oil pressure
On high-hour engines a faulty sender and a real loss of pressure look the same on the controller. A mechanical gauge test separates them.
Heat on large engines: Overheating
On K-series and QSK sets, a blocked radiator core or slipping fan belt causes shutdowns late in a long outage.
Wet stacking on standby sets: Wet stacking
A large set run on no-load tests, or on a small load through load shedding, builds up unburnt fuel in the exhaust.
Voltage and the alternator: Stamford alternators
Low, high or unstable voltage is traced through the AVR, exciter, rotating diodes and windings of the Stamford or other alternator fitted.
PowerCommand alarms and settings: Control panel repairs
PowerCommand keeps a fault and event history; reading it before a reset often shows the cause. Settings changed after a repair must suit the installation.
Read the plates before you call
Servicing a Cummins set, point by point
Intervals and parts follow the engine model, its hours and its duty. A service covers:
- Engine oil and filters to the grade for the engine, with the old oil checked for fuel, coolant or metal
- Fuel filters and the water separator, with water drained from the tank where there is a drain point
- Coolant strength, hoses, the radiator core and, where fitted, the coolant filter
- Air filter restriction, the turbocharger and the charge-air pipework
- Belts, the fan drive, batteries, the battery charger and the starter motor
- The controller’s event history and settings, and any stored engine fault codes on QS engines
- A test run, under load where the site allows, with voltage and frequency recorded
A standby set that seldom runs is serviced by the calendar, not the hour meter. See service intervals and oil care.
Parts for Cummins engines and sets
Parts are identified from the plates: the ESN and CPL for the engine, the alternator plate for the AVR and bearings, and the set nameplate for the controller. Service items are genuine Cummins parts or quality equivalents made to the same specification, and the quote says which. For an old PT pump or a discontinued PowerCommand board, a rebuilt unit or a modern controller may be the practical route.
To book generator repairs, a generator service or a maintenance plan, send the set and engine plates, the hour-meter reading and a photo of any alarm.
Independent service
We Service & Repair All Generator Brands
Onsite Generator Repairs is an independent generator specialist. We repair, service and maintain Cummins equipment as part of our work on every make of generator.
Manufacturer warranty claims go through the manufacturer’s own network. If your generator is still under warranty, check the warranty terms before arranging work by anyone else.
Brand names and trademarks belong to their respective owners. Onsite Generator Repairs is an independent service and repair company.
Service areas
Where we work in Gauteng
FAQ
Frequently asked questions
Can you work on a Cummins engine in a set built by another company?
Yes. The engine is serviced the same way whoever built the set. The controller, alternator and wiring belong to the set builder, so we check those against what is actually fitted.
Why does my Cummins standby set smoke when it runs on test?
Some white smoke on a cold start is normal. Black smoke on a set that only runs without load can point to wet stacking, injectors or an air restriction. See generator smoke.
My Cummins set shows a fault code. Should I just reset it?
Photograph the code first. A reset clears the alarm, but the history we use to find the cause stays in the controller and ECM. If the set stopped on low oil pressure or high temperature, do not keep restarting it. See controller alarms explained.
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Who we work for
Need a generator technician?
- 24/7 operations
- We Arrive Within 1–2 Hours (usually within 1 hour)
- Free callouts and quotations