Mobile Onan RV Generator Repair Across Florida

Onan built its reputation on reliability, and that reputation is deserved. A QG 4000 that has been properly maintained will run for 3,000 hours or more without major work. A QD 8000 diesel in a well-kept diesel pusher can outlast the coach. The problems that bring these units to a halt are almost never catastrophic - they are carburetor circuits fouled by ethanol, pressure senders that have corroded through hundreds of heat cycles, fuel pumps that have pumped their last gallon, and control boards that have absorbed one too many voltage spikes from Florida thunderstorms.

Triton RV Repair has been diagnosing and repairing Onan generators in Florida since 2014. Jesse Marcer founded the company with the premise that mobile service is almost always better than a shop visit for generator work: the Onan is mounted in the coach, the coach is at a campground or storage lot, and towing a 40-foot Class A to a dealer for a carburetor clean is expensive and unnecessary.

Reading Onan Fault Codes Without a Diagnostic Tool

Onan builds a fault code readout directly into the control board of every QG and QD generator, and it requires no tool to access. With the generator off and in standby mode, press and hold the start/stop button until the status LED begins flashing. Count the blinks carefully: the LED will pause between the two digits of the fault code, then repeat the sequence twice before stopping. A code 36, for example, appears as three blinks, a distinct pause, then six blinks.

The code is stored in non-volatile memory, so it persists after a shutdown and will still be there when you power the generator back up hours later. This matters because it means a technician arriving after the fact can still read the code that triggered the original shutdown, without having to recreate the fault condition. Most owners are surprised to learn this feature exists - the Onan manual describes it but buries the information well past the point where most people stop reading.

Common codes you will see on Florida coaches include code 36 (oil pressure sender fault), code 12 (high temperature), code 45 (governor circuit), and code 13 (overspeed). Each has a distinct set of likely causes and a corresponding diagnostic sequence. A fault code is a starting point for diagnosis, not a final answer.

Fault Code 36 - Low Oil Pressure and the Sender Problem

Code 36 is a protective shutdown triggered when the oil pressure signal drops below the threshold the control board expects. The critical distinction that saves most owners from unnecessary engine work is this: the oil pressure signal comes from an electromechanical sender, and that sender fails regularly. When the sender fails open, it sends a zero-pressure signal to the board regardless of actual oil pressure. The generator shuts down within seconds of starting, the control board stores code 36, and the engine is completely unharmed.

Before any engine work begins, verify actual oil level. If the oil is at the correct level and the generator runs cleanly for the first few seconds before shutting down, the sender is the overwhelmingly likely cause. A mechanical pressure gauge can be installed on the sender port to confirm actual pressure during a start attempt. In the vast majority of field calls where code 36 appears on a properly-filled engine, the sender is the problem and a new sender clears it for good.

Genuine low oil pressure - from a worn oil pump, a failed pressure relief valve, or bearing damage - produces a different presentation. The engine typically sounds different at start, may run rough or develop a knock, and real low-pressure conditions will reappear even after a sender replacement. If you are on the road and the code returns immediately after a new sender, add a quart of oil as a precaution and call for a mechanical gauge test before running the generator further.

The 30-Second Shutdown - Choke Circuit and Carburetor Varnish

An Onan QG 4000 that starts, runs for approximately 30 seconds, and then dies is showing a textbook presentation of a stuck choke circuit. The choke is designed to close during cold starts and then release as the engine warms up. When the pilot circuit in the carburetor is blocked with ethanol-varnish deposits, the choke either does not release fully or releases too slowly. The engine starts on the rich mixture the closed choke provides, then floods out or loses power as the choke should open but cannot.

Florida's climate accelerates this problem. Ethanol-blended gasoline degrades quickly in heat, and the pilot circuit in the QG 4000 carburetor has passages fine enough that even a light varnish deposit is sufficient to cause a restriction. A generator that sits unused during the summer - a common situation for snowbirds who leave their coaches in storage - will almost certainly have this issue when it is started in the fall.

The fix is a thorough carburetor clean or rebuild. The carburetor comes off the generator, all circuits are cleared with carb cleaner and compressed air, and the float height and needle settings are verified before reinstallation. In cases where the pilot circuit passages are corroded rather than just varnished, a rebuild kit with new passages is the more reliable repair. The entire job is typically completed at the coach in under two hours.

QG 4000 vs. QD Series - Different Platforms, Different Failures

The QG 4000 is a gasoline generator fitted to Class C motorhomes and smaller Class A gasoline coaches. It uses a carbureted engine and is the more common unit in Florida's rental and entry-level coach population. Its primary failure modes are carburetor-related, and they are almost entirely caused by fuel quality issues and storage conditions. The QG 4000 is straightforward to diagnose and repair at the coach.

The QD 5500, QD 6500, and QD 8000 are diesel generators fitted to diesel pusher coaches. They share fuel with the chassis engine, eliminating the stale-gasoline problem, and they are considerably more robust under sustained load. Diesel Onan units typically fail in different areas: fuel lift pumps that develop leaks or lose prime, injection pump wear at very high hours, and control board failures from electrical transients. A QD unit that is hard to start when hot but starts fine when cold is almost always showing a fuel lift pump problem rather than an injection issue.

The diagnostic and repair procedures for QG and QD units are not interchangeable. A technician trained only on gasoline generators will not necessarily know the QD fuel system well, and vice versa. Triton RV Repair works on both platforms across Florida.

Idle vs. Load Behavior and What Each Tells You

One of the most useful diagnostic observations an owner can report is how the generator behaves differently at idle compared to when an appliance is running. An Onan that runs rough at idle but smooths out under load is showing a classic carburetor lean-idle condition: the idle circuit is not supplying enough fuel, but the main circuit takes over under load and compensates. This points directly to a dirty or blocked idle jet and is resolved with a carburetor service.

The reverse situation - a generator that runs fine at idle but surges, loses power, or shuts down under load - points to a different set of problems. Main circuit restrictions, a fuel pump that cannot maintain adequate flow under demand, a failing choke pull-off, or a governor circuit issue can all produce this pattern. A QD diesel that performs well unloaded but cannot maintain voltage when the air conditioner starts is often showing a fuel lift pump at the limit of its flow capacity.

Reporting this behavior accurately when you call is valuable. It narrows the diagnostic before the technician arrives and often means the right parts are on the van rather than requiring a second visit. Jesse Marcer has found that owners who describe what the generator does rather than what code it threw give the most useful information, since behavior patterns reveal the failure mechanism in a way that fault codes alone do not always capture.

Control Board Failures and How to Distinguish Them

Onan control boards are solid-state units that manage starting, voltage regulation, speed governing, and fault detection. Florida's electrical environment is hard on boards: lightning-induced voltage spikes travel through shore power connections and campground pedestals, and a board that has absorbed several of these events will eventually show erratic behavior or fail entirely. A generator that produces unstable voltage, throws random fault codes with no clear pattern, or behaves differently on each start attempt is often showing a board that is failing intermittently rather than any mechanical problem with the engine.

Board failures are confirmed by substitution in the field. Boards are model-year specific on Onan generators - a board from a QG 4000 built in 2012 is not compatible with one built in 2018, even though the generator looks identical on the outside. Ordering the correct board requires the model number and spec number from the data plate on the generator itself, not just the generator model name. Triton RV Repair carries common board configurations in stock for the most frequently-seen Florida units.

A board replacement is completed at the coach in most cases. The old board is disconnected, the harness connections are photographed before removal, the new board is installed and the connections are verified, and a full load test confirms stable output before the call is closed. The load test matters: a board fault that seemed electrical can sometimes trace back to a mechanical governor issue that the new board exposes differently.

Lifespan, Overhaul, and Replacement Decisions

A QG 4000 maintained on its oil change schedule - every 100 hours or annually, whichever comes first - with fresh fuel and clean air filter will routinely reach 3,000 hours. At that point, ring wear and valve recession become factors. The unit will still run but may struggle to maintain voltage under heavy load and will consume more oil. A full engine overhaul - rings, valves, head gasket, and carburetor rebuild - restores output and extends the service life by another 2,000 hours or more, at a fraction of the cost of a new generator.

The math changes when the engine has suffered a hard failure such as a spun bearing, a bent connecting rod, or a seized cylinder. Those failures usually mean coolant or fuel has contaminated the oil, and the internal damage is extensive enough that an overhaul is not economically justified. In that scenario, a remanufactured long block or a complete replacement generator is the practical path. Triton RV Repair will tell you plainly which situation you have before recommending a direction, and the assessment is part of the service call, not an additional charge.

For QD diesel units, the overhaul threshold is considerably higher. A well-maintained QD 8000 can exceed 6,000 hours with nothing more than lift pump replacements and routine service. The diesel engine's inherent efficiency and the absence of ethanol-related carburetor damage means the QD simply lasts longer under the same conditions. When a QD does need engine work, it is typically injection pump reconditioning or sleeve and piston replacement - larger jobs, but still economically justified given the cost of a diesel generator replacement.

Onan Generator Repair Pricing in Florida

Frequently Asked Questions

Sources

• Cummins Onan service and parts portal

  HDKAJ, HGJAB, and QD series fault codes, wiring diagrams, and repair manual access.

• Cummins Onan RV generator specs

  QG 4000, QD 5500, and QD 8000 specifications, oil capacity, and service weight.