Generac NP66G troubleshooting: 11 symptom-cause-remedy entries from the manufacturer's own service documentation.
Generac NP66G — full specs, parts & maintenance.
| Symptom | Cause | Remedy |
|---|---|---|
| ENGINE WON’T CRANK | TEST 1 - CHECK 5 AMP FUSE GOOD: REPLACE FUSE OR REPLACE TEST 2 - CHECK BATTERY GOOD: RECHARGE TEST 3 - CHECK STARTER CONTACTOR BAD: REPLACE | |
| ENGINE CRANKS, BUT WON’T START | TEST 8 - CHECK FUEL SHUTOFF VALVES GOOD: FILL TANK OPEN VALVE(S) CHECK FILTER(S) TEST 11 - CHECK ENGINE IGNITION SYSTEM BAD: REPLACE OR REPAIR TEST 12 - CHECK MODULE BAD: REPLACE OR REPAIR TEST 14 - CHECK ENGINE CONDITION BAD: ADJUST, REPLACE AS NECESSARY | |
| ENGINE STARTS, SHUTS DOWN WHEN START/STOP SWITCH IS RELEASED | TEST 16 - CHECK ENGINE OIL LEVEL GOOD: REPLENISH TEST 17 - CHECK OIL PRESSURE SWITCH GOOD: REPLACE OR BAD: REPLACE TEST 18 - CHECK OIL TEMPERATURE SWITCH GOOD: REPLACE OR BAD: REPLACE | |
| ENGINE STARTS HARD, RUNS ROUGH | TEST 12 - CHECK CARBURETION GOOD: ADJUST, REPAIR AS NECESSARY TEST 14 - CHECK ENGINE CONDITION BAD: REPLACE OR REPAIR | |
| ENGINE WON’T SHUT DOWN | TEST 16 - CHECK WIRE #18 GOOD: REPLACE OR REPAIR BAD: REPLACE | |
| LOW OR NO A-C GENERATOR OUTPUT | TEST 20 - CHECK LINE BREAKERS BAD: REPLACE OR REPAIR VOLTS/FREQUENCY BOTH GOOD: DISCONTINUE TESTS VOLTS/FREQUENCY BOTH HIGH OR LOW: TEST 23 - CHECK LOAD VOLTAGE AND FREQUENCY TEST 24 - ADJUST ENGINE GOVERNOR | |
| Engine Won't Crank. | 1. 15 amp fuse biown. 2. Loose, corroded or defective battery cable(s). 3. Battery is discharged or defective. 4. Defective starter contacior. 5. Defective starter motor. 6. Defective control relay (CR1). | 1. Repiace biown fuse. 2. Tighten, clean or replace, as necessary. 3. Recharge or repiace battery. 4. Replace starter contactor. 5. Replace starter motor. 6. Replace control relay. |
| Engine Cranks, won't Start. | 1. Out of fuel. 2. Fuel shutoff valve(s) in fuel supply line are closed. 3. Fuel pump not operating. 4. Automatic choke not operating properly. 5. Engine is flooded. 6. Fuel filter clogged. 7. Defective Control Relay (CR2). 8. Engine spark plugs defective. 9. Bad ignition magneto on engine. 10. Bad carburetor. 11. Dirty air cleaner. | 1. Refill tuel tank. 2. Open fuel shutoff valve(s). 3. Repair or replace bad pump. 4. Repair, replace or adjust. 5. Wait 5-10 minutes, try again. 6. Replace if clogged. 7. Replace bad relay CR2 8. Clean, regap or replace as necessary. 9. Replace if defective. 10. Adjust, repair or repiace. 11. Clean or replace as needed. |
| Engine Starts Hard, Runs Rough | 1. Dirty engine air cleaner. 2. Automatic choke is sticking. 3. Defective spark plugs. 4. Defective ignition magneto. 5. Water in fuel. | 1. Clean or replace as needed. 2. Free choke linkage as needed: 3. Clean, regap or replace. 4. Replace if bad. 5. Drain tank and refill. |
| Engine Starts, then Shuts Down | 1. Engine oil level is low. 2. Bad control relay (CR1) 3. Bad low oil pressure switch. 4. Bad control relay (CR2) | 1. Add oil as needed. 2. Replace if bad. 3. Replace if bad. 4. Replace bad relay CR2 |
| No a-c Output Voltage | 1. Main breaker(s) open. 2. Transfer switch (if so equipped) is set to wrong position. 3. Failure in vehicle electrical system. 4. Generator component failure. | 1. Close main breaker(s). 2. Reset transfer switch. 3. See vehicle manual. 4. Contact an authorized service facility. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: 1. 15 amp fuse biown. 2. Loose, corroded or defective battery cable(s). 3. Battery is discharged or defective. 4. Defective starter contacior. 5. Defective starter motor. 6. Defective control relay (CR1).. See the table for the matching fixes.
Documented causes: 1. Out of fuel. 2. Fuel shutoff valve(s) in fuel supply line are closed. 3. Fuel pump not operating. 4. Automatic choke not operating properly. 5. Engine is flooded. 6. Fuel filter clogged. 7. Defective Control Relay (CR2). 8. Engine spark plugs defective. 9. Bad ignition magneto on engine. 10. Bad carburetor. 11. Dirty air cleaner.. See the table for the matching fixes.
Documented causes: 1. Dirty engine air cleaner. 2. Automatic choke is sticking. 3. Defective spark plugs. 4. Defective ignition magneto. 5. Water in fuel.. See the table for the matching fixes.