For a different Onan model, but it's likely to be valid info anyway.
OVERFREQUENCY – FAULT CODE 14
WARNING Some genset service procedures present hazards that can result in severe personal injury
or death. Only trained and experienced persons with knowledge of fuels, electricity, and machinery
hazards should perform genset service. See Safety Precautions.
Logic: Instantaneous Fault – Frequency greater than 70Hz
Delayed Fault – Frequency greater than 66Hz, but less than 70Hz, for 3 continuous seconds
Possible Causes: Genset loads, Inverter/Charger, engine governor function, fuel supply, air fuel mixture, exhaust
system, choke, demand regulator, carburetor, generator drive system, generator windings, ignition, wire
connections
Diagnosis & Repair:
1. Verify that Last Fault is FC 14: Yes, continue diagnosis; No, troubleshoot actual last fault.
2. Measure AC current while running genset with vehicle loads: identify faulty or short cycling loads.
3. Determine battery charge rate (typical default is 80 percent): if adjustable reduce to 30 percent.
4. Measure genset load capability with shop load bank (derate for altitude and temperature as necessary).
5. Measure genset frequency and droop while running.
6. Measure AC frequency while changing engine rpm to determine if frequency response matches engine
rpm response: repair damaged generator drive system as necessary.
7. Disconnect genset control P1 connector, verify P1 pins are fully inserted and inspect pin condition per
PSB–676: insert, repair or replace pins as necessary.
8. Reconnect P1 connector and test run genset for fault occurrence: repair or replace pins in connector as
necessary.
9. Check all grounds and neutral leads for looseness at battery, genset, inverter/converter; run genset on
separate battery: tighten or replace terminals and leads as necessary.
10. Check air filter cleanliness; replace air filter as necessary.
11. Check for blocked or damaged exhaust system: repair or replace exhaust components as necessary.
12. If the genset will not stay running measure genset frequency, quadrature winding and main winding voltages
using Break-Out Tool 420–0603 and Instruction Sheet R1098.
13. Gasoline Models
A. Vapor lock may occur in high ambient temperatures: operate in ambients at less than 120°F; verify
proper installation to prevent air recirculation; correct as necessary.
B. Verify steady DC voltage at fuel pump while genset is running; repair wiring as necessary.
C. Run genset on shop fuel supply; verify tank level and fuel line condition in vehicle.
D. Verify carburetor altitude setting; readjust as necessary.
E. Verify choke operation, setting and linkage damage; readjust, repair or replace as necessary.
F. Measure throttle stop frequency; readjust as necessary.
G. Measure fuel pump pressure/flow: replace fuel filter or pump as necessary.
