Carburetor assembly
Part: Onan B-144016
Common overcrank fix when an RV generator sat with stale fuel and will not start after fuel and spark checks.
$67
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Onan RV Generator Error Codes
Onan (Cummins-owned) RV generators are the most common motorhome and camper generators on the market. Marquis, MicroLite, and Emerald series use LED flash codes on older units and digital code displays on newer Quiet Diesel Series controllers.
Onan LED Flash Code Table (Marquis, Emerald, MicroLite)
| Flashes | Fault | Common Cause | Fix |
|---|---|---|---|
| 1 | Low oil pressure | Oil level low or switch fault | Check oil, test switch at 3-8 PSI |
| 2 | High temperature | Coolant or airflow restriction | Clean radiator screen, check coolant |
| 3 | Overspeed/overvoltage | RPM or voltage too high | Test governor, AVR, throttle linkage |
| 4 | Overcrank | Failed to start in 3 attempts | Check fuel, spark, choke operation |
| 5 | Low oil level (float switch) | Float switch stuck or low oil | Check oil level, test float switch |
| 6 | No AC output (brushless) | Voltage regulator or rotor fault | Test AVR, flash field, check diodes |
Onan Quiet Diesel Series Codes (Digital Display)
| Code | Fault | Common Cause | Fix |
|---|---|---|---|
| 3 | Overspeed | Engine over 70 Hz | Check governor actuator, fuel pressure |
| 4 | Overcrank | No-start after attempts | Check fuel system, glow plugs, battery |
| 5 | Low oil pressure | Under 10 PSI | Check oil level, pressure sender |
| 6 | High coolant temp | Over 220°F | Clean radiator, verify fan operation |
| 7 | Service shutdown | Internal fault | Read sub-code on display |
| 8 | Service air filter | Air filter restricted | Replace air filter |
| 9 | Low fuel | Fuel level low | Add fuel |
| 10 | Battery voltage low | Under 11V | Charge battery, test charger |
| 11 | Sensor 1-4 fault | Failed sensor | Replace indicated sensor |
| 12 | Overload (kW) | Electrical load too high | Reduce load |
Most Common Onan Generator Faults
Overcrank (4 Flashes)
The most common Onan fault, especially on RV generators that sit for months between trips. Stale fuel in the carburetor is the #1 cause. Onan engines have a fuel pump, carburetor, and choke system that gum up with ethanol-blended fuel. Fix: drain the carburetor bowl, use fresh fuel with stabilizer. If the generator hasn’t run in 6+ months, the carburetor likely needs cleaning or replacement.
No AC Output (6 Flashes)
The engine runs fine but no power at the RV outlets. Onan brushless generators lose residual magnetism after storage. Quick fix: with the generator running, momentarily connect a 12V test light or drill between the brush leads to flash the field. On some models, running the generator at full RPM for 30 seconds with no load is enough to self-excite.
Low Oil Pressure (1 Flash)
Onan generators have a low oil pressure switch wired to the controller. If the switch senses below 3-8 PSI (depending on model), it shuts down. On RV generators, this is often caused by the generator being parked on an incline — the oil pickup can’t reach the oil. Level the RV first, then check oil level.
Parts Reference
| Part | Approx Cost | Notes |
|---|---|---|
| Carburetor assembly | $45-$90 | Onan B-144016, fits most single-cylinder |
| Fuel pump | $30-$60 | Onan 149-2392 |
| Voltage regulator (AVR) | $50-$120 | Onan 305-0796 |
| Oil pressure switch | $15-$30 | Onan 122-1109 |
| Ignition coil | $20-$40 | Onan 166-0756 |
| Spark plug | $5-$8 | Champion RC12YC, gap 0.030” |
Need Replacement Parts?
Before ordering, match the generator part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.