Mechanical and Systems Services / In shop only
RV Generator Repair in Yorba Linda
RV generator repair covers the engine, the alternator end and the controls on an Onan or Cummins set. Service and repair is published at $400 to $8,500 and up across 2 to 35 labor hours. The overwhelming majority of failures trace to fuel and to disuse rather than to electrical parts.
The single most useful sentence in generator ownership is this: these engines are damaged far more often by sitting than by running. An owner who runs a generator two hours every month will keep it healthy for fifteen years. An owner who runs it twice a summer will be rebuilding a carburetor every other season.
The reason is fuel. Modern gasoline with ethanol content absorbs moisture and forms gum and varnish within months. That deposit settles in the smallest passages in the fuel system, which on a small generator carburetor are very small indeed. Diesel sets have their own version involving microbial growth and injector deposits.
Onan or Cummins: what is actually in the compartment?
They are the same product line. Onan was acquired by Cummins and the sets are now branded Cummins Onan, so an older coach carries an Onan badge and a newer one carries Cummins branding on essentially the same architecture. Parts availability is generally good across both, which is one reason we work on them so routinely.
The practical distinction is fuel and family. Gasoline sets in the Marquis and Microlite families are common on Class C and gas Class A coaches, drawing from the vehicle fuel tank. Diesel sets in the Quiet Diesel family are standard on diesel pushers and draw from the main diesel tank. Liquid propane sets appear on some towables and specialty builds.
All of them share a fuel pickup arrangement that surprises owners: the generator pickup tube in the vehicle fuel tank is deliberately shorter than the engine pickup. That is a safety feature, so the generator runs out of fuel before you strand the vehicle. It also means a generator that dies at a quarter tank is behaving exactly as designed, and we get that call several times a season.
Why does a generator that starts fine refuse to hold a load?
Because starting requires very little fuel and running an air conditioner requires a lot. A set that fires immediately, idles happily and then stumbles or drops out when the load comes on is describing a fuel delivery restriction almost every time.
The sequence is predictable. Varnish narrows the main jet, so the carburetor can supply enough for no load operation but not enough for full output. Or a fuel pump is weak, or a filter is partly blocked, or the pickup screen in the tank is fouled. All of those present identically: fine unloaded, collapses under load.
Owners and unfortunately some shops jump to the electrical end, replacing control boards, voltage regulators and brushes. Those parts do fail, but they usually fail differently. A genuine alternator end fault more often produces no output at all, output at the wrong voltage, or output that never comes up, rather than output that starts and then sags under demand. Testing under a controlled load tells you which category you are in within an hour.
- Starts and runs unloaded, drops out under air conditioning: fuel delivery
- Cranks and will not fire at all: fuel supply, ignition or a control lockout
- Runs but produces no AC output: alternator end, breaker or control board
- Output voltage or frequency out of range: governor, regulator or engine speed
- Shuts down after several minutes: overheat, low oil pressure or exhaust restriction
What does under-loading do to a generator?
It carbons it up, and this is the least understood part of generator ownership. These sets are designed to run at a substantial percentage of their rated output. Running a 5,500 watt set with nothing on but a phone charger means the engine runs cool, combustion is incomplete and unburned fuel deposits carbon on the valves, in the cylinder and through the exhaust.
The visible result is wet stacking on diesel sets, where unburned fuel and soot accumulate and eventually weep from the exhaust. On gasoline sets the result is carbon on the valve seats, which leads to poor sealing, hard starting and eventually a burned valve.
The prevention is free and takes two hours a month: run the set with a real load on it. Two air conditioners, or an air conditioner plus a water heater on electric, is a reasonable target. Exercising a generator unloaded is better than not running it at all, but it is not the same thing and it will not clear existing carbon.
What does generator work cost?
Generator service and repair on Onan and Cummins sets is published at $400 to $8,500 and up across 2 to 35 labor hours at the posted $260 per hour mechanical rate.
The bottom of that band is a routine service: oil, filters, plugs, air filter and a load test. The middle is a carburetor rebuild or replacement, a fuel pump, a starter or a control board. The top is a major overhaul or a full set replacement, where access frequently costs as much labor as the mechanical work because the generator lives in a slide out tray behind a bay wall.
Diagnostics are $285 per hour with a one hour minimum, refundable as a credit against an authorized repair. On generators that hour is usually decisive, because a controlled load test separates fuel faults from alternator faults immediately.
What Is Included
- 01Compartment inspection for rodent nesting, debris and exhaust integrity
- 02Oil, coolant and fuel condition assessment before starting
- 03Start, run and stability observation with no load applied
- 04Controlled load test with real loads applied in stages
- 05Output voltage and frequency measurement across the load range
- 06Fuel delivery testing from the tank pickup through to the carburetor or injectors
- 07Exhaust system inspection for leaks, since a generator exhaust leak is a carbon monoxide risk
- 08Written findings with a repair path before any parts are ordered
Our Process and Timeline
Shop hours and calendar days are different things. These are the stages and the realistic duration of each.
- 011 hour
Compartment and safety inspection
Before anything runs, we inspect for nesting material, fuel weeping and exhaust leaks. A generator exhaust leak into a coach is a fatality risk.
- 0230 minutes
Cold start observation
How a set behaves in the first sixty seconds tells you a great deal. Cranking speed, first fire, stumble and stabilization are all recorded.
- 031 to 2 hours
Staged load testing
Loads are applied in stages while voltage, frequency and engine behaviour are watched. This is what separates fuel faults from alternator faults.
- 041 to 3 hours
Fuel system testing
Supply pressure and volume are verified from the tank pickup forward, because a restriction anywhere in that path produces the same symptom.
- 051 day
Repair authorization
Written findings and a quoted repair go to you. Diagnostic time credits against the authorized work.
- 061 to 12 days
Repair and reverification
Work is performed, then the same staged load test is repeated so the fix is proven under the conditions that exposed the fault.
Common Problems and How We Solve Them
The generator starts and runs but drops out when the air conditioner comes on.
SolutionFuel delivery restriction in almost every case. We test supply from the tank pickup forward and rebuild or replace whichever element cannot deliver full load volume.
A control board was replaced elsewhere and the fault came back.
SolutionThe board was likely never the cause. We load test first, which separates fuel and engine faults from genuine alternator end faults before any part is ordered.
The generator quits at a quarter of a tank of fuel.
SolutionThat is the shortened generator pickup tube working as designed so you cannot strand the vehicle. It is not a fault, and understanding it saves an unnecessary repair.
Black soot weeps from the generator exhaust on a diesel coach.
SolutionWet stacking from chronic under-loading. We clear the accumulation, inspect for damage and set you up with a realistic loaded exercise schedule so it does not return.
Specific Services
Frequently Asked Questions
How much does RV generator repair cost?
Published at $400 to $8,500 and up across 2 to 35 labor hours at the posted $260 per hour rate. Routine service sits near the bottom, carburetor and fuel work in the middle, and overhaul or replacement at the top.
How often should I run my RV generator?
About two hours a month with a real load applied, meaning air conditioning or an electric water heater rather than a phone charger. Unloaded running is better than nothing but it does not prevent carbon buildup.
Is my generator an Onan or a Cummins?
Both, in practice. Cummins acquired Onan and current sets are branded Cummins Onan. Parts and service procedures carry across, so an older Onan badge does not mean orphaned equipment.
Why will my generator not start after sitting all winter?
Ethanol blended fuel forms gum and varnish in months, and generator carburetor passages are extremely small. Stale fuel is the first thing we check, and stabilizing fuel before storage prevents most of these calls.
Can you replace a generator with a larger one?
Sometimes. The limits are compartment dimensions, fuel supply, exhaust routing and the coach transfer switch and wiring capacity. We assess all four before quoting, because a set that does not fit the electrical system is not an upgrade.
Do you work on liquid propane generators?
Yes, and LP work is performed by certified technicians only. LP fuelled sets are common on towables and specialty builds and carry their own regulator and pressure requirements.
Vehicles We Perform This On
Related Services
We Can Help. Contact Us Today.
Bring the vehicle to our Yorba Linda facility and we will document the damage properly, work directly with your carrier, and give you a written figure built from published rates and real labor hours.
All work is performed at our Yorba Linda facility. We do not offer mobile, roadside or fleet route service.