Cummins/Onan 4A2.3 Engine Engine

• Voltage is unstable, high or low
  Fix: Push to reset breaker. Does generator AC output voltage build up? If no, flash exciter field per TEST [D]. Does generator output voltage build up?
• Residual voltage across terminals 2 and 3 of VR21 is less than 5 to 10 VAC
  Fix: Disconnect stator leads from leads 1 and 2 from AC across the leads. Is residual voltage 4 and 5,5 VDC or more now? Check reactor CMR21 and transformer T21 per TESTS (B) and (E). For shorts per TEST [MI.
• NO AC OUTPUT VOLTAGE AT RATED ENGINE RPM
  Fix: Check lead continuity between AC terminals on A1 and terminals 2 and 3 on VR21 per TEST [Ml. Replace defective field breaker. Remove one lead from breaker and check continuity with ohmmeter. Is breaker open? Is control panel field breaker CB21 on?
• Engine starts but stops after running several seconds.
  Cause: A fault condition indicated by fault breaker CB12 on control panel or DC control breaker trips when the generator set is started.
  Fix: Check for a possible fault condition. If none, check fault monitors S1 through S5 and fault breaker CB12 for improper wiring. Check all B+ wiring for shorts to ground.
• Engine does not crank.
  Cause: Battery dead.
  Fix: Check battery per Checkout [A] and recharge or replace. Check battery charger operation per jumper battery cable B+ connection to 81 starter solenoid terminal. Does engine crank? If no, check battery cables for clean tight connections and motor-if bad, repair or replace. (ref. Checkout [B]). Check B1 starter solenoid With S11 in Start position, is battery voltage present between K11 terminal S and ground? If not, check B+_/wiring between K11 and B1 solenoid terminal. Replace if bad. If K11 does not energize, test per Checkout [D] and replace if bad. Is battery voltage present at B1 solenoid terminal with S11 in Start position. Check breakers CB11, CB13, or fuse F1. Check S11 and replace if bad. Check B+/wiring to S11 start terminal and K11 -S terminal.
• Engine cranks but does not start.
  Cause: Heater circuit operating improperly or incorrect fuel.
  Fix: Check heater solenoid K13 per Checkout [HI. Check diodes CR2 and CR3, wiring, heaters, and resistors START. Check fuel supply system: fuel tank level, shutoff valves, fuel lines and connections, fuel filters, transfer pump and injection blue-white, and fuel flow steady from fuel return line. Check fault reset breaker. Check B+ circuit through K11-I to Engine monitor board terminal All-1, All-CB12 Line, All-SW B+, to K1. Does K1 fuel solenoid energize when S l l is in Start position? Incorrect fuel? See Operator’s Manual recommendations.
• SWITCH OFF lamp flashes.
  Fix: 8. *12-Light Panel Only.
• PRE LO OIL PRES lamp lights. Engine continues to operate.
  Fix: 4. Indicates engine oil pressure has dropped to 20 psi (138 kPa). If generator is powering critical loads and cannot be shut down, wait until next shutdown period and then follow step 5 procedure. If engine can be stopped, follow procedures in step 5.
• PRE HI ENGINE TEMP lamp lights. Engine continues to operate.
  Fix: 1. Green RUN lamp lights following engine start-up. 2. Indicates engine has begun to overheat and engine temperature has risen to approximately 202°F (94°C). If generator is powering non-critical and critical loads and cannot be shutdown, use the following: a. Reduce load if possible by turning off non-critical loads. b. Check air inlets and outlets and remove any obstructions to airflow. c. Open doors or windows in generator area to increase ventilation. If engine can be stopped, follow procedure in step 3.
• OVERCRANK lamp lights and engine stops cranking.
  Fix: 6. *12-Light Panel Only. Engine runs, shuts down, and LO OIL PRES lamp lights.
• NO AC output voltage.
  Fix: Field breaker is tripped. Reset breaker. Contact an authorized dealer or distributor if voltage build up causes breaker to trip.
• LO OIL PRES lamp lights. Engine shuts down.
  Fix: 5. Indicates engine oil pressure has dropped to 14 psi (97 kPa). Check oil level, lines and filters. If oil system is okay but oil level is low, replenish. Reset control and restart. Contact an authorized dealer or distributor if oil pressure is not in the range of 30 to 55 psi (206 to 379 kPa).
• LO FUEL lamp lights. Engine shuts down and LO OIL PRES lamp lights.
  Fix: 10. *12-Light Panel Only.
• LO FUEL lamp lights. Engine continues to run.
  Fix: 9. *12-Light Panel Only.
• HI ENG TEMP lamp lights. Engine shuts down.
  Fix: 4. Indicates engine has overheated (engine temperature has risen above 222°F/106°C) or coolant level is low (sets with coolant level sensor). Allow engine to cool down completely before proceeding with the following checks: a. Check coolant level and replenish if low. Look for possible coolant leakage points and repair if necessary. b. Check for obstructions to cooling airflow and correct as necessary. c. Check for a slipping fan belt and tighten if loose. d. Reset control and restart after locating and correcting problem. Contact an authorized dealer or distributor if none of the above.

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan 4A2.3.

Pooled from every document that names this exact engine — confirm the interval and part number against your unit's serial number.