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Generac GT-999 Engine

The Generac GT-999 is a 1 L 2-cylinder naturally aspirated engine rated at 3600 rpm. It powers generator sets from Generac, including the 15 kW EcoGen, 20 kW Synergy, 8.1 GN and G0070420. It holds 1.8 L (0.5 gal) of oil.

Also known as: GT-999, Generac GT-999

0.999 L

Displacement

Cylinders

3600 rpm

Rated speed

1.8 L

Oil capacity

On this pageSpecs Generator sets Maintenance FAQ Service intervals Torque & specs Fluids Fault codes Procedures Wiring

Engine specifications

Oil capacity	1.8 L
Displacement	0.999 L
Cylinders	2
Aspiration	Naturally aspirated
Rated speed	3600 rpm

Generator sets powered by this engine

Generac 15 kW EcoGen Generac 20 kW Synergy Generac 8.1 GN Generac G0070420

How to read your Generac engine serial & model number →

Common problems

Unit will not start in AUTO with utility loss
Cause: Start delay countdown
Fix: If the start up delay is greater than expected, contact servicing dealer to adjust from 2 to 1500 seconds.
Engine cranks but won't start
Cause: Fuel supply and pressure faulty
Fix: Test 66 - Check fuel supply and pressure; find and correct cause of no fuel or low pressure
Engine cranks but will not start
Cause: No fuel
Fix: Replenish fuel / turn on fuel valve.
No transfer to standby after utility source failure
Cause: MLCB (generator disconnect) is OFF (OPEN)
Fix: Reset generator disconnect to ON (CLOSED).
Engine starts hard and runs rough
Cause: Air cleaner plugged or damaged
Fix: Check and clean air cleaner.
Unit consumes large amounts of oil
Cause: Excessive engine oil
Fix: Adjust oil to proper level.
Engine will not crank
Cause: Blown fuse
Fix: Correct short circuit condition by replacing 7.5 amp fuse in generator control panel. Contact an Independent Authorized Service Dealer (IASD) if fuse continues to blow.
Yellow LED illuminated in any state LOW BATTERY
Fix: Clear alarm. Check the battery using the control panel under the MAIN menu using the BATTERY MENU option. If it states battery is GOOD contact servicing dealer. If it states CHECK BATTERY replace the battery.
Engine will not crank when AUTO-OFF-MANUAL switch is set to "MANUAL"
Cause: Battery faulty
Fix: Test 61 - Check battery; replace
Unit will not start in AUTO with utility loss. NOT ACTIVATED
Cause: Unit not activated
Fix: Refer to activation section in owners manual.
Generator produces zero voltage or residual voltage (12-20 kW)
Cause: Main circuit breaker open or failed
Fix: Reset to "ON" or replace if bad
Engine starts hard and runs rough / lacks power / backfires
Cause: Fuel supply and pressure faulty
Fix: Test 66 - Check fuel supply and pressure; find and correct cause of no fuel or low pressure
No AC output from generator
Cause: Main line circuit breaker (MLCB) (generator disconnect) is OFF (OPEN)
Fix: Reset generator disconnect to ON (CLOSED).
Unit will not start in AUTO with utility loss — LED RED LOW OIL PRESSURE
Cause: Check LEDs / screen for alarms
Fix: Check oil level and add oil as needed. If oil level is correct, contact an IASD
Unit will not start in AUTO with utility loss — LED: RED LOW OIL PRESSURE
Fix: Check oil level and add oil as needed. If oil level is correct, contact an IASD.

Compiled from service & troubleshooting documentation across every generator set that uses the Generac GT-999.

Maintenance schedule

Item	Spec	Capacity	Part #	Interval
Air filter			0J8478	1000 hr	Amazon eBay $20.00 NAPA $24.32 KuduParts $15.00
Oil filter	American Petroleum Institute (API) Service Class SJ, SL or better		070185E	500 hr	Amazon eBay $30.00 NAPA $9.09 FridayParts $45.99
Battery			0H3421S		Amazon eBay $283.32
Oil	SAE 30 (above 32°F), 10W-30 (40°F to -10°F), Synthetic 5W-30 (all temperatures)	3.55 liters	—	500 hr
Spark plug			RC12YC	1000 hr	Amazon eBay $12.90 NAPA $11.52 FridayParts $19.99

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

Repair guides

Step-by-step procedures compiled from the Generac service manual for this engine.

Service intervals

Item	Action	Hours	Months	Notes
Oil	Change	200 hr	24 mo	First service — Change oil after first eight (8) hours of operation
Oil filter	Change	200 hr	24 mo	First service — Change oil filter after first eight (8) hours of operation
Aceite del motor	Change	25 hr		First service — Después del período de asentamiento de 25 horas, se recomienda utilizar el aceite 5W-20 propiedad de Generac para uso continuo.
Oil and filter	Change	25 hr		First service — After first 25 hours of operation
Valve Clearance	Check	400 hr	6 mo	First service — Check/adjust after first 25 hours of operation
Engine governor oil level	Check	50 hr		Check prior to initial use and every 50 operating hours thereafter.
Change oil	Change	100 hr		Yearly or 100 hours
Engine oil and filter	Replace	100 hr	12 mo	First service — After first 25 hours; then every 100 hours or 1 year. Cold weather (<4.4°C) or continuous hot (>29.4°C): every 100 hours or 1 year
Oil cooler	Clean	100 hr		20 kW models; Yearly or 100 hours
Coolant Level and Hoses	Check	125 hr	12 mo	Schedule A; also daily if running continuously
Enclosure Louvers	Check	125 hr	12 mo	Schedule A; also daily if running continuously
Fuel Lines	Check	125 hr	12 mo	Schedule A; also daily if running continuously
Lubricating Oil Level and Drain Hose	Check	125 hr	12 mo	Schedule A; also daily if running continuously
Lubricating Oil and Oil Filter	Replace	125 hr	12 mo	First service — Schedule A
Radiator for Clogging	Check	125 hr	12 mo	Schedule A; also daily if running continuously
Air cleaner service	Clean	150 hr		Yearly or hours shown
Exercise	Test	168 hr		Weekly exercise
Aceite de motor y filtro de aceite	Change	200 hr	24 mo	First service — Programa de mantenimiento A
Air cleaner	Replace	200 hr	24 mo	Inspect and replace as necessary; 2Y or 200 hours
Batería (condición, nivel de electrolito y estado de carga)	Check	200 hr	24 mo	Programa de mantenimiento A
Battery condition	Check	200 hr	24 mo	Schedule A.
Battery condition and charge	Check	200 hr	24 mo	Schedule A maintenance
Change Air Filter	Change	200 hr		200 hours or 2 years
Change Oil & Filter	Change	200 hr		200 hours or 2 years; 20kW: 100 hours or 2 years
Complete tune-up	Other	200 hr	24 mo	To be completed by a dealer; 2Y or 200 hours
Engine oil	Change	200 hr	24 mo	First service — Up to a 2 year/200 hour oil change interval.
Huile à moteur et filtre à huile	Change	200 hr	24 mo	First service — Calendrier A: tous les deux ans ou toutes les 200 heures. Changer l'huile et le filtre après les 25 premières heures. En conditions froides (moins de 4,4 °C/40 °F) ou fonctionnant en continu à plus de 29,4 °C/85 °F, changer annuellement ou toutes les 100 heures.
Inspect Air Filter	Inspect	200 hr		200 hours or 2 years
Inspect Spark Plugs	Inspect	200 hr		200 hours or 2 years
Oil filter	Replace	200 hr	24 mo	200 hours or 2 years, whichever occurs first
Replace filter (oil)	Replace	200 hr		14 kW: Yearly or 200 hours; 20 kW: Yearly or 100 hours
Service Schedule A	Other	200 hr	24 mo	200 hours or 2 years
Óleo lubrificante e filtro de óleo	Change	200 hr	24 mo	First service — Trocar após as primeiras 25 horas; Programação A (2 anos ou 200 h); em clima frio (<4,4 °C) ou quente contínuo (>29,4 °C) anualmente ou 100 h
Air cleaner service	Replace	300 hr		Yearly or hours shown; service more frequently under dusty/dirty conditions
Brushes and collector ring	Inspect	300 hr		Yearly or 300 hours; authorized distributor/dealer only
Aceite del motor y filtro de aceite	Replace	400 hr	48 mo	First service — Programa B: cada cuatro años o 400 horas.
Air cleaner	Clean	400 hr		Clean or replace as necessary; R = Replace as Necessary; 400 hours
Air cleaner	Inspect	400 hr	24 mo	Inspect and change; every 400 hours
Air filter	Replace	400 hr	48 mo	Schedule B maintenance
Battery condition, electrolyte level, and state of charge	Inspect	400 hr	48 mo	Schedule B

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Service specifications

Type	Item	Value	Unit	Condition
Clearance	Belt deflection	3/8 - 5/8	in	22 Ibs (10 kgf) force midway between water pump and alternator pulleys
Clearance	Belt deflection	7.6 - 12.7	mm	22 Ibs (10 kgf) force midway between water pump and alternator pulleys
Clearance	Valve clearance	0.002 - 0.004 inch (0.05 - 0.1 mm)	inch (mm)	engine cool
Gap	Armature Air Gap	0.008-0.012	inch
Gap	Breaker Point Gap	0.018-0.022	inch
Gap	Folga da vela de ignição	0,020	pol
Gap	Folga da vela de ignição	0,040	pol
Gap	Folga da vela de ignição	0,508	mm
Gap	Folga da vela de ignição	1,02	mm
Gap	Ignition magneto air gap	0.008-0.012	inch
Gap	Ignition magneto air gap	0.008-0.012 inch (0.20-0.30 mm)	gap	V-twin engines; fixed non-adjustable on single cylinder
Gap	Ignition magneto air gap (V-twin)	0.008-0.012 inch (0.20-0.30 mm)	inch / mm
Gap	Ignition magneto gap to flywheel (replacement)	0.010 inch	inch
Gap	Separación de electrodos de bujía (11 kW)	0.030	in (0.76 mm)
Gap	Separación de electrodos de bujía (16/20/22 kW)	0.040	in (1.02 mm)
Gap	Separación de electrodos de bujía (9 kW)	0.020	in (0.508 mm)
Gap	Separación de las bujías	0.508	mm (0.020 pulg.)
Gap	Separación de las bujías	1.02	mm (0.040 pulg.)
Gap	Spark Plug Gap	0.030	in (0.76 mm)	11 kW (GTH-530)
Gap	Spark Plug Gap	0.031-0.035	inch
Gap	Spark Plug Gap	0.040	in. (1.02 mm)
Gap	Spark Plug Gap (1.5L engines, 25/30 kW)	0.9	mm
Gap	Spark Plug Gap (2.4L engines, 22/27/36/45 kW)	1.07-1.17	mm
Gap	Spark Plug Gap (32/38 kW and 60 kW)	0.71	mm
Gap	Spark plug gap	0.020	in (0.508 mm)
Gap	Spark plug gap	0.020 in (0.508 mm)	in (mm)
Gap	Spark plug gap	0.040 in (1.02 mm)	in (mm)
Gap	Spark plug gap	0.508	mm
Gap	Spark plug gap	0.76	mm (0.030 inch)
Gap	Spark plug gap	0.76 mm (0.030 inch)	gap	410 cc and 530 cc engines
Gap	Spark plug gap	1.02	mm (0.040 inch)
Gap	Spark plug gap	1.02 mm (0.040 inch)	gap	990 cc and 999 cc engines
Gap	Spark plug gap (10 kW)	0.020	in (0.508 mm)
Gap	Spark plug gap (11 kW)	0.030	in (0.76 mm)
Gap	Spark plug gap (12/14/16/17/20 kW)	1.02	mm
Gap	Spark plug gap (14-24 kW)	0.040	in (1.02 mm)
Gap	Spark plug gap (14–24 kW)	0.040	in (1.02 mm)	cold
Gap	Spark plug gap (16/20/22 kW)	0.040	in (1.02 mm)
Gap	Spark plug gap (8/10 kW)	0.76	mm
Gap	Spark plug gap (9 kW)	0.020	in (0.508 mm)
Gap	Spark plug gap 10kW	0.030 inch	inch
Gap	Spark plug gap 13/14/15/16/17kW	0.040 inch	inch
Gap	Spark plug gap 20kW	0.030 inch	inch
Gap	Spark plug gap 8kW	0.030 inch	inch
Gap	Écartement des électrodes des bougies d'allumage	0.508	mm (0,020 po)
Gap	Écartement des électrodes des bougies d'allumage	0.76	mm (0,030 po)
Gap	Écartement des électrodes des bougies d'allumage	1.02	mm (0,040 po)
Other	Cold Smart Start fixed temperature	20 F (-7 C)	F (C)	22-26 kW
Other	Cold Smart Start fixed temperature	50 F (10 C)	F (C)	10-20 kW
Other	Compression Ratio (1.5L)	11:1
Other	Compression Ratio (2.4L)	9.5:1
Other	Compression Ratio GH-410	8.6:1
Other	Compression Ratio GT-530	9.5:1
Other	Compression Ratio GT-990	9.5:1
Other	Compression Ratio GT-999	9.5:1
Other	Compression difference maximum between cylinders	25 percent	percent
Other	Compression ratio	8.6:1
Other	Compression ratio	9.5:1
Other	Cylinder leak down acceptable leakage	20	percent
Other	Exercise time length (16-22 kW)	5	minutes

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Recommended fluids

Fluid	Grade	Standard	Capacity	Notes
Coolant	50 percent soft water and 50 percent ethylene glycol base anti-freeze	low silicate anti-freeze	2.0 U.S. gallons	Do not use chromate base rust inhibitor or high silicate anti-freeze boosters.
Coolant	50/50 ethylene glycol	Generac 50/50 ethylene glycol type coolant	9.5 liters	Use demineralized or distilled water; do not use propylene glycol. Coolant mix 40-60% volume.
Engine oil	10W-30	API Service Class SJ, SL or better		For expected operating temperatures between 40 °F and -10 °F
Engine oil	30 weight organic oil (factory fill)			Units run and tested at factory prior to shipping, no break-in required
Engine oil	5W-20	Generac proprietary 5W-20 Synthetic (after 30 hour break-in)	3.8 liters	Factory filled with 5W-20; 60 kW capacity 5.25 quarts (5 liters). Do not use special additives.
Engine oil	5W-20 (Generac proprietary)	API Service Class SJ, SL, or better	1.03 L	Oil capacity including filter. Use for continuous use after the 25 hour break-in period; specifically formulated for gaseous powered Generac generators. Do not use special additives. Change every year or 100 hours in cold weather (below 40 F) or continuous hot weather (above 85 F).
Engine oil	5W-30	Aceite orgánico 5W-30 (la unidad se entrega de fábrica llena con este aceite)		Compruebe el nivel de aceite y, de ser necesario, añada la cantidad apropiada con la viscosidad correcta. No llene en exceso. Consulte 'Recomendaciones para el aceite de motor' para tipo/viscosidad.
Engine oil	5W-30 (factory fill) / 5W-20 GEO (continuous)	Generac proprietary gaseous engine oil (GEO)		Unit comes filled with 5W-30 organic oil; after 25 hour break-in use 5W-20 GEO
Engine oil	5W-30 or 10W-30	API Service Class SG, SH, or SJ synthetic oil	1.8 L	14 kW models; capacity 1.8 L (1.9 qt.)
Engine oil	SAE 10W-30			RM92-8M0086220U6 / RM92-8M0086221U3
Engine oil	SAE 15W-40			RM92-8M0096794U3; diesel engines
Engine oil	SAE 25W-40			RM92-8M0086227U3 / RM92-8M0086224U3
Engine oil	SAE 30	API Service Class SJ, SL or better		For expected operating temperatures above 32 °F
Engine oil	SAE 30 above 32°F; 10W-30 between 40°F and -10°F; Synthetic 5W-30 10°F and below	API Service Class SJ, SL or better; use no special additives	1.5 Qts	Oil capacity including filter
Engine oil	SAE 40 above 86 F; SAE 30 32-85 F; SAE 20W below 32 F; SAE 10W-30 all seasons	API Service SC, SD, SE or SF	3.0 U.S. quarts	Liquid-cooled 1.2 liter engine with filter change; 2.5 U.S. quarts without filter change.
Engine oil	SAE 5W-30 Synthetic	API Service Class SJ, SL or better		Do not use special additives
Engine oil	SAE 5W-30 sintético	API SJ, SL o mejor	1.03 l	9 kW; no usar aditivos especiales
Engine oil	SAE 5W-30 synthetic; SAE 30 above 60 F; SAE 10W-30 20-59 F; SAE 5W-20/5W-30 below 20 F	API Service SF, SF/CC, or SF/CD	1.5 U.S. quarts	Air-cooled V-Twin engine crankcase capacity about 1.5 U.S. quarts. Oil makeup tank capacity about 2.5 U.S. quarts on Model 9067.
Engine oil	SAE 5W-30 synthétique	API classe de service SJ, SL ou supérieure		Huile SAE 5W-30 synthétique pour toutes les plages de température. N'utilisez aucun additif spécial.
Engine oil	Synthetic 5W-30	API Service Class SJ, SL or better		For expected operating temperatures 10 °F and below
Engine oil	Synthetic SAE 5W-30	API SJ, SL, or better	3.75 Quarts (3.55 Liters)	For all temperature ranges; do not use special additives
Engine oil	TC-W3	TC-W3		2-cycle outboard oil; RM92-858026QB1U6 / RM92-858027QB1U3 / RM92-858037QB1U3
Fuel		Gas natural: contenido de BTU de por lo menos 1000 BTU/ft3 (37,26 MJ/m3). Gas LP: por lo menos 2500 BTU/ft3 (93,15 MJ/m3)	250.0 gal (946 l)	Tamaño mínimo del tanque de LP es 250 gal (946 l), salvo que los cálculos de la unidad indiquen uno mayor. Solo sistema de extracción de vapor para LP.
Fuel	Gas natural	mínimo 1000 BTU por pie cúbico (37.26 megajulios por metro cúbico)		Reducciones típicas de gas natural 10-20 % respecto a LP
Fuel	Gaz naturel		37.26 mégajoules par mètre cube (1 000 BTU par pied cube) minimum	Teneur en BTU minimale du gaz naturel.
Fuel	Gaz naturel d'au moins 37,26 mégajoules par mètre cube (1 000 BTU par pied cube)	NFPA 54
Fuel	Gaz propane liquide (gazeux)		93.15 mégajoules par mètre cube (2 500 BTU par pied cube) minimum	Capacité de réservoir de gaz propane liquide minimum recommandée de 946 litres (250 gallons).
Fuel	Gaz propane liquide d'au moins 93,15 mégajoules par mètre cube (2 500 BTU par pied cube)	NFPA 58 / ICC IFGC		Réservoir de gaz propane liquide d'une capacité minimale de 946 litres (250 gallons).
Fuel	LP (vapor)	mínimo 2500 BTU por pie cúbico (93.15 megajulios por metro cúbico)	946.0 l	Se recomienda tanque de LP de 250 gal. (946 l) de tamaño mínimo si se convierte de NG a LP
Fuel	LP Gas	at least 2,520 Btus per cubic foot		Vapor withdrawal; required pressure 10-12 inches water column

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Fault codes

Code	Name	Meaning	Severity	Action
1048	VSCF Overload	Unit shuts down during operation	Shutdown	Alternator, AVR or wiring damaged. Contact servicing dealer.
1049	VSCF Overload	Unit shuts down during operation	Shutdown	Generator output shorted or severely overloaded; clear overload and restart
1051	VSCF High Battery	Yellow LED illuminated in any state	Warning	Voltage supply to AVR is high; check external battery charger installation or contact servicing dealer
1052	VSCF DC Overvoltage	Unit shuts down during operation	Shutdown	Generator temporarily overloaded or output shorted; try restart
1053	VSCF Gate Fault	Unit shuts down during operation or starting	Shutdown	AVR is damaged; contact servicing dealer
1054	VSCF IGBT Overtemp.	Unit shuts down during operation or starting	Shutdown	Replace AVR filter, inspect fan, check intake/exhaust, check ambient temperature; contact servicing dealer
1055	VSCF Phase Error	Unit shuts down during starting	Shutdown	Check stepper motor, linkage, gas pressure; contact servicing dealer if alternator damaged
1056	VSCF Undervoltage	Unit shuts down during operation or starting	Shutdown	Load too large, remove and restart; or alternator/AVR damage, contact servicing dealer
1057	VSCF Overvoltage	Unit shuts down during operation or starting	Shutdown	Generator overloaded; remove load and restart
1058	VSCF DC Undervoltage	Unit shuts down during operation or starting	Shutdown	Alternator damage; contact servicing dealer
1059	VSCF Field Loss	Unit shuts down during starting	Shutdown	Alternator damage; contact servicing dealer
1060	Big Fan Failure	Unit shuts down during operation	Shutdown	AVR electronics exceeded 70°C; replace AVR filter, check intake/exhaust/ambient temp; contact servicing dealer
1061	VSCF Field Loss	Unit shuts down during operation	Shutdown	Alternator damage; contact servicing dealer
1065	Overfrequency	Unit shuts down during operation	Shutdown	Overload, RPM sensor failure, or stepper motor problem; contact servicing dealer
1066	VSCF Speed mismatch	Unit shuts down during operation or starting	Shutdown	Fuel pressure loss, large overload, or throttle/engine problem; contact servicing dealer
1070	Small fan failure	Small fan failure displayed; continues 80 minutes without fan if running in AUTO	Warning	Check fan wiring/mechanical, check AVR filter for blocked air path
1100	Overcrank	Engine Cranks but will not Start (5 crank attempts)	Shutdown	Problem 17
1200	Overspeed	Prolonged over specified Hz for 3 seconds	Shutdown	Test 12
1205	Overspeed	Instantaneous over specified Hz for 0.1 second	Shutdown	Test 12
1207	Overspeed	Monitors zero cross timing of AVR; 150 ms of 4500 rpm or higher	Shutdown	Test 64 and Test 60
1300	Low Oil Pressure	Occurred while running; check oil level and pressure	Shutdown	Test 61
1400	High Temperature	Air flow impeded; check inlet/outlet for debris	Shutdown	Test 62
1501	RPM Sensor	Twin Cylinder+Running; RPM sensor loss	Shutdown	Test 50 and Test 64
1505	RPM Sensor	Twin Cylinder+Cranking; RPM sensor loss	Shutdown	If engine cranks, Test 64. If not crank, Problem 15.
1511	RPM Sensor	Single Cylinder+Running; RPM sensor loss	Shutdown	Test 50 and Test 64
1515	RPM Sensor	Single Cylinder+Cranking; RPM sensor loss	Shutdown	If engine cranks, Test 64. If not crank, Problem 15.
1600	Underspeed	Unit is overloaded, slowing engine speed, fuel supply low or throttle control problem	Shutdown	Problem 3, or Test 50, or Test 12
1800	Overvoltage	Prolonged over-voltage	Shutdown
1900	Undervoltage	Prolonged under-voltage; below 80% for 10+ seconds	Shutdown	Preliminary Output Voltage Test
1901	Undervoltage	Instantaneous under-voltage due to sudden loss of voltage	Shutdown	Preliminary Output Voltage Test
1902	Undervoltage	Both zero crosses missing; faulty excitation winding or zero cross circuit	Shutdown	Preliminary Output Voltage Test
1906	Undervoltage	Single zero cross missing; faulty excitation winding or zero cross circuit	Shutdown	Preliminary Output Voltage Test
2099	Wiring Error	Mis-wired; customer connection low voltage and high voltage wires crossed	Shutdown	Check customer connection in generator
2100	Overload Remove Load	Overloaded - Default; one or both CTs detecting overload	Shutdown	Remove Load
2299	Undervoltage Overload	Unit was overloaded and attempted to start with large load	Shutdown	Remove Load
2399	Stepper Overcurrent	Current flow in stepper coil(s) above specification	Shutdown	Test 12
2400	Fuse Problem	Missing or damaged 7.5 amp controller fuse	Shutdown	Test 44
2800	Aux Shutdown	External shut down circuit is open	Shutdown	Check continuity of harness and operation of switch(es). Repair/replace as needed.
AC Sens Loss Shutdwn	Loss of AC sensing shutdown	Controller shut down the generator because there was less than 5% of rated voltage measured on Phase A for 3 seconds, only in AUTO.	Shutdown	Check for loose wiring and connections. Check all AC leads. Troubleshoot alternator.
AC Sens Loss Warning	Loss of AC sensing warning	Controller measured less than 5% of rated voltage on Phase A for 1 second, 10 seconds after crank disconnect.	Warning	Check for loose wiring and connections. Check all AC leads. Troubleshoot alternator.
Aux Input Shutdwn	Auxiliary input shutdown	Digital input for a custom shutdown (AuxiliaryInputShutdown - PIM) was activated (low).	Shutdown	Check customer equipment connected to the PIM module.
AUXILIARY SHUTDOWN	Auxiliary Shutdown	Unit will not start	Shutdown	Set auxiliary shutdown switch(es) to CLOSED (I); clear alarm
BATERÍA BAJA	BATERÍA BAJA	Indicador LED amarillo encendido en cualquier estado.	Warning	Borre la alarma. Navegue hasta BATTERY MENU del MAIN MENU para revisar la batería. Si indica GOOD, comuníquese con un IASD. Si indica CHECK BATTERY, reemplace la batería.
Battery CRLow Warning	Battery cranking low warning	Battery voltage dropped to 11 VDC or less for 30 seconds or more.	Warning	Check engine starting battery. Check battery charger DC output voltage from RDC2.
Battery High Warning	Battery high warning	Battery voltage above the high warning setting for 10 seconds or more.	Warning	Check engine starting battery.
Battery Low Warning	Battery low warning	Battery voltage below the low warning setting for 90 seconds or more.	Warning	Check engine starting battery. Check battery charger DC output voltage from RDC2.
BATTERY PROBLEM	Battery Problem	Yellow LED illuminated	Warning	Contact servicing dealer
Battery Problem	Battery Fault	Battery condition poor or battery charger issue	Warning	Inspect battery condition and connections. Contact IASD if needed.
CARGADOR SIN CA	CARGADOR SIN CA	Indicador LED amarillo encendido en cualquier estado.	Warning	Comuníquese con un IASD.
CHARGER MISSING AC	Charger Missing AC	AC power unavailable for battery charging	Warning	Restore AC power supply or check generator AC output.
CHARGER WARNING	Charger Warning	Yellow LED illuminated	Warning	Contact servicing dealer
Controller Fault	Control Module Failure	Internal controller fault detected	Shutdown	Contact IASD for assistance
CONTROLLER FAULT	Controller Fault	Alarm message listed on controller menu.	Shutdown	Contact an IASD.
DESCONEXIÓN AUXILIAR	DESCONEXIÓN AUXILIAR	La unidad no arranca.	Shutdown	Coloque los interruptores de desconexión auxiliar en posición CERRADA (I).
DOWNLOAD FAILURE	Download Failure	Firmware download or update failed	Warning	Retry firmware update. Contact authorized service dealer if problem persists.
Emerg Stop Shutdwn	Emergency stop shutdown	Optional emergency stop button pressed or emergency stop leads ESS and/or ESN are not connected.	Shutdown	Reset the emergency stop button and clear the fault; check ESS and ESN connections; if no E-stop, connect ESS and ESN together.
EMERGENCY STOP	Emergency Stop	Alarm message listed on controller menu.	Shutdown	Check emergency shutdown switch and reset.
Engine M/N Invalid Shutdwn	Engine model number invalid shutdown	Generator model number has not been entered.	Shutdown	Enter the generator set model number from the RDC2 keypad, or use SiteTech to select the genset model number.
Engine Speed High Shutdwn	Engine speed high shutdown	Engine speed, calculated from AC frequency, was above the high speed setting for 0.3 seconds or more.	Shutdown	Troubleshoot engine operation per the engine service manual.
Engine Speed Low Shutdwn	Engine speed low shutdown	Engine speed below the low speed setting for 3 seconds or more after crank disconnect; enclosure thermostat may have tripped.	Shutdown	Troubleshoot engine per engine service manual. Check for high enclosure temperatures and reset the thermostat.
EXERCISE SET ERROR	Exercise Set Error	Exercise timer setting error	Warning
Exercise Set Error	Exercise Set Error	Warning; displayed if the exercise period becomes corrupted	Warning	Reset the exercise period to clear
Frequency High Shutdwn	Frequency high shutdown	Frequency measured on Phase A exceeded the high frequency setting for 10 seconds, 10 seconds or more after crank disconnect.	Shutdown	Troubleshoot engine operation per the engine service manual.
Frequency Low Shutdwn	Frequency low shutdown	Frequency on Phase A was less than the low limit for 10 seconds, or 10 Hz or more less than rated for 60 seconds or more.	Shutdown	Troubleshoot engine per engine service manual. Check for high enclosure temperatures and reset the thermostat.
FUEL PRESSURE	Fuel Pressure	Fuel pressure warning	Warning
FUSE PROBLEM	Fuse Problem	Unit will not start in AUTO with utility loss	Warning	Check 7.5amp fuse, replace with ATO 7.5Amp fuse if bad
High Engine Temperature	High Engine Temperature	Shutdown alarm, auto reset; 10 second delay on start-up and 1 second delay before shutdown; contacts close if temperature exceeds approximately 144 °C (293 °F)	Shutdown	Auto reset when condition clears and restart engine if a valid start signal is present
High Lube Oil Temperature Shutdown	High lube oil temperature shutdown	Oil temperature higher than 325 F (163 C).	Shutdown	See Overheats in the troubleshooting charts in Section 5.14.
High Lube Oil Temperature Warning	High lube oil temperature warning	Oil temperature higher than 300 F (149 C).	Warning	See Overheats in the troubleshooting charts in Section 5.14.
HIGH TEMPERATURE	High Temperature	Unit shuts down during operation	Shutdown	Check ventilation around generator, intake, exhaust and rear of generator
High Temperature	Overheat	Engine operating temperature too high	Shutdown	Inspect ventilation around generator, intake, exhaust, and rear. Ensure no obstructions present.
INSPECCIONE LA BATERÍA	INSPECCIONE LA BATERÍA	Indicador LED amarillo encendido en cualquier estado.	Warning	Inspeccione la batería. Presione ENTER para borrar.
INSPECT BATTERY	Inspect Battery	Battery inspection reminder	Info	Inspect battery; press ENTER to clear.
INTERNAL FAULT	Internal Fault	Internal controller fault	Shutdown	Contact servicing dealer.
Internal Fault	Internal Fault	Shutdown alarm; this alarm cannot be cleared	Shutdown	Call service dealer
Lo Crank Vlt Warning	Low cranking voltage warning	During cranking, battery voltage measured less than 60% (7.2V or 14.4V) for 6 seconds or more.	Warning	Check cranking battery.
Locked Rotor Shutdwn	Locked rotor shutdown	No rotation of the engine or alternator was detected for 3 seconds or more during cranking.	Shutdown	Check cranking circuit. Troubleshoot the engine and alternator. Check alternator connections to controller and auxiliary winding circuit breaker.
LOW BATTERY	Low Battery	Yellow LED illuminated	Warning	Clear alarm; check battery via control panel BATTERY MENU; if GOOD contact dealer, else replace battery
Low Battery	Battery Voltage Low	Starting battery voltage below acceptable level	Warning	Inspect battery and battery cables. Charge or replace battery if necessary.
LOW OIL PRESSURE	Low Oil Pressure	Unit will not start in AUTO with utility loss	Shutdown	Check oil level / add oil per Owners Manual

Showing the first 80 of 127 codes.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Procedures

Adjust Magneto Flywheel Gap adjustment

Tools: 0.008-0.012 inch thickness gauge, screwdriver

Rotate flywheel until magnet under module.
Insert 0.008-0.012 inch non-metallic thickness gauge.
Loosen mounting screws.
Let magnet pull magneto against gauge.
Tighten screws.
Remove gauge by rotating flywheel.

Adjust Valve Clearance adjustment

⚠ Allow engine to cool before adjusting valve clearance

⚠ AVR fan operates for 80 minutes after shutdown

Tools: 13mm wrench, 10mm Allen wrench, Feeler gauge

Remove spark plug wires and spark plugs
Remove four screws attaching valve cover, discard gasket
Verify piston at top dead center (TDC) of compression stroke
Loosen rocker jam nut with 13mm wrench
Turn pivot ball stud with 10mm Allen wrench while checking clearance with feeler gauge
Tighten jam nut to 174 in-lbs (19.68 Nm) while holding pivot ball stud
Recheck valve clearance
Install new valve cover gasket and valve cover, torque fasteners to 60 in-lbs (6.8 Nm) in cross pattern
Install spark plugs, torque to 18 ft-lbs (25 Nm)
Connect AVR fan and 4-pin connector
Install AVR filter housing, torque to 50-96 in-lbs (6-11 Nm)
Repeat for other cylinder if necessary

Adjust ignition magneto air gap — V-twin adjustment

Tools: 0.008-0.012 inch thickness gauge

Rotate flywheel until magnet is under module laminations.
Place 0.008-0.012 inch (0.20-0.30mm) thickness gauge between magnet and laminations.
Loosen mounting screws and let magnet pull magneto against gauge.
Tighten both mounting screws.
Rotate flywheel to remove thickness gauge.
Repeat for second magneto.

Adjusting GH-410/GT-530/990/999 Valve Clearance adjustment

⚠ The engine should be cool before checking.

Tools: Feeler gauge, 10mm allen wrench, Socket wrench

Remove spark plug wires and position wires away from plugs.
Remove spark plugs.
Make sure the piston is at Top Dead Center (TDC) of its compression stroke.
Make sure the engine is at 60 to 80 F.
Remove the four screws attaching the valve cover.
Loosen the rocker jam nut.
Use a 10mm allen wrench to turn the pivot ball stud while checking clearance between the rocker arm and valve stem with a feeler gauge.
When valve clearance is correct, hold the pivot ball stud in place and tighten the rocker arm jam nut to 174 in/lbs torque.
Recheck valve clearance.
Install new valve cover gasket and re-attach the valve cover.
Install spark plugs and re-attach the spark plug wire.
On the GT-530 and GT-990/999, repeat the process for the other cylinder.

Adjusting Magneto Flywheel Gap adjustment

⚠ Air gap between ignition magneto and flywheel on single cylinder engines is not adjustable.

Tools: 0.008-0.012 inch thickness gauge

Rotate the flywheel until the magnet is under the module (armature) laminations.
Place a 0.008-0.012 inch (0.20-0.30mm) thickness gauge between flywheel magnet and module laminations.
Loosen the mounting screws and let the magnet pull the magneto down against the thickness gauge.
Tighten both mounting screws.
To remove the thickness gauge, rotate the flywheel.
Repeat the above procedure for the second magneto.

Adjusting Valve Clearance adjustment

⚠ Risk of Burn. Allow the engine to cool before performing the following procedure.

Tools: Feeler gauge, 10 mm wrench, 13 mm wrench, 14 mm wrench, 10 mm hex key

Allow engine to cool before adjusting valve clearance.
Remove spark plug wire(s) away from plugs and remove spark plug(s).
Remove the four screws attaching the valve cover; remove and discard gasket.
Verify piston is at TDC of its compression stroke (both valves closed).
Loosen rocker jam nut using a 10 mm wrench (10 kW) or 13 mm wrench (20–22 kW).
Turn pivot ball stud with a 14 mm wrench (10 kW) or 10 mm hex key (20–22 kW) while checking clearance with a feeler gauge.
Hold pivot ball stud and tighten rocker arm jam nut to specification.
After tightening jam nut, verify valve clearance did not change.
Install new valve cover gasket and valve cover; tighten fasteners in a cross pattern.
Install spark plugs and tighten to 18 ft-lbs (25 Nm).
Attach spark plug wire to spark plug.
Repeat process for other cylinder if equipped.

Adjusting Valve Clearance GH-410/GT-530/990/999 adjustment

⚠ Check valve clearance after first six (6) months of operation.

Tools: 10mm allen wrench, Feeler gauge, Socket and socket wrench

Engine should be cool before checking; clearance 0.002-0.004 inch needs no adjustment.
Remove spark plug wires and spark plugs.
Set piston at Top Dead Center of its compression stroke.
Remove four screws attaching the valve cover.
Loosen rocker jam nut; turn pivot ball stud with 10mm allen wrench.
Set clearance to 0.002-0.004 inch (0.05-0.1 mm).
Hold pivot ball stud and tighten jam nut to 174 in/lbs torque.
Install new valve cover gasket and re-attach valve cover.

Adjusting the Fuel Regulator - 7kW (Natural Gas Only) adjustment

⚠ Do not make any unnecessary adjustments. Factory settings are correct for most applications.

Tools: frequency meter

Start the generator; let it stabilize and warm up at no-load.
Connect a frequency meter across the generator's AC output leads.
Turn the primary adjust screw to obtain a frequency reading.

Ajustar a folga das válvulas adjustment

⚠ Risco de queimaduras. Deixe o motor esfriar antes de executar o procedimento.

Tools: Chave de 10 mm, Chave de 13 mm, Chave de 14 mm, Chave sextavada de 10 mm, Calibrador

Remova os fios das velas de ignição e remova as velas de ignição.
Remova os quatro parafusos que prendem a tampa da válvula; descarte a junta.
Verifique se o pistão está no TDC do seu curso de compressão.
Solte a contraporca do balanceiro (C) com chave de 10 mm ou 13 mm.
Gire o pino de esfera articulada (D) com chave de 14 mm ou sextavada de 10 mm e ajuste a folga.
Aperte a contraporca do braço oscilante e inspecione a folga novamente.
Instale a nova junta e as tampas das válvulas; aperte em padrão transversal.
Instale as velas e aperte a 25 Nm; conecte os fios das velas.

Ajuste de la luz de válvulas adjustment

⚠ Dejar enfriar el motor antes de ajustar.

⚠ Iniciar los cuatro tornillos antes de apretar.

Tools: Calibre de espesores, Llaves de 8/10/13/14 mm, Llave de casquillo, Casquillo grande

Cerrar la válvula de combustible y desconectar la batería.
Retirar cable(s) de bujía y alejarlos.
Retirar la(s) bujía(s).
Llevar el pistón al PMS de la carrera de compresión.
Retirar los cuatro tornillos de la cubierta de válvulas y desechar la junta.
Aflojar la contratuerca del balancín.
Girar el prisionero de bola pivote para ajustar la luz con calibre.
Sostener el prisionero y apretar la contratuerca; verificar y reinstalar con junta nueva.

Ajuste de la separación de la válvula adjustment

⚠ Deje que el motor se enfríe antes del procedimiento.

⚠ Desconecte el cable negativo y luego el positivo de la batería.

⚠ No necesario en unidades 14 o 18 kW con motor de 816 cc.

Tools: Llave de 10 mm, Llave de 13 mm, Llave de 14 mm, Llave hexagonal de 10 mm, Galga de espesores

Retire los hilos de las bujías y las bujías.
Retire los cuatro tornillos de la cubierta de la válvula y deseche la junta.
Verifique que el pistón esté en el PMS de su carrera de compresión.
Suelte la contratuerca del balancín (llave 10 mm en 10 kW, 13 mm en 20 a 24 kW).
Gire el espárrago del pivote (llave 14 mm en 10 kW, hexagonal 10 mm en 20 a 24 kW) ajustando la separación.
Sostenga el espárrago y apriete la contratuerca del balancín.
Inspeccione la separación para verificar que no cambió.
Instale una junta nueva y la cubierta de la válvula; apriete en patrón cruzado.
Instale las bujías y apriete a 25 Nm (18 lb-pie).
Conecte los hilos de las bujías.

Check and Adjust Accessory / Drive Belt adjustment

Tools: Belt deflection gauge

Inspect belt for cracks, fraying, excessive wear or other damage.
Verify belt is free of grease and oil; replace if contaminated.
Using a suitable gauge, apply 22 Ibs (10 kgf) force midway between water pump and alternator pulleys.
Loosen DC alternator tension bracket screw.
Rotate alternator outward to reduce belt deflection.
Rotate inward to increase belt deflection.
Tighten DC alternator tension bracket screw to 17-22 ft-lbs (23-30 Nm).
Recheck belt deflection and repeat steps as necessary.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Voltage reconnection

Voltage	Phase	Connection	Leads	Notes
		0 – c.c. (-)	NOIR no 3	Fil de mise à la terre normal; obligatoire si jumelé à un commutateur de transfert de gestion intelligente de l'alimentation de Generac.
		23	BLANCO Núm. 5	Cable de señal lógica del control de transferencia
		23 (White #5)	E	Transfer Control Signal Wire
		Control system interconnections	N1, N2, 0, 15B, 23	Can be run in same conduit as AC power if length < 35 feet and all wiring rated 600V
		Generator control wiring - 1-115 ft (1-35 m)	N1, N2, T1, 23, 194	No. 18 AWG
		Generator control wiring - 116-185 ft (36-56 m)	N1, N2, T1, 23, 194	No. 16 AWG
		Generator control wiring - 186-295 ft (57-89 m)	N1, N2, T1, 23, 194	No. 14 AWG
		Generator control wiring - 296-460 ft (90-140 m)	N1, N2, T1, 23, 194	No. 12 AWG
		Longueur de fil 1 à 35 m (1 à 115 pi)	Calibre 18 AWG	Conducteurs en cuivre seulement.
		Longueur de fil 35 à 56 m (115 à 185 pi)	Calibre 16 AWG	Conducteurs en cuivre seulement.
		Longueur de fil 56 à 89 m (185 à 295 pi)	Calibre 14 AWG	Conducteurs en cuivre seulement.
		Longueur de fil 89 à 140 m (295 à 460 pi)	Calibre 12 AWG	Conducteurs en cuivre seulement.
		Neutral for battery charger	WHITE NEU/00	Must be connected to keep battery charged whether unit is running or not
	1	Connect a 2008 and later load center switch to a pre-2008 air-cooled generator: Wire 0 will not be utilized. Remove battery charger from the transfer switch. Connect N1 (BLU) to N1 (YEL), N2 (YEL) to N2 (YEL), 23 (BRN) to 23 (WHT), 194 (ORG) to 15B (RED) using UL approved wire nuts.	N1, N2, 23, 194, 15B, 0	Battery charger in transfer switch will not be utilized in operation of the generator.
	1	Connect a pre-2008 load center switch to a current or future air-cooled generator: Wire 0 will not be utilized. Connect N1 (BLU) to N1 (YEL), N2 (YEL) to N2 (YEL), 23 (BRN) to 23 (WHT), 194 (ORG) to 15B (RED) using UL approved wire nuts.	N1, N2, 23, 194, 15B, 0	Wire 194 changed to 15B on current model air-cooled generators.
	1	Single-phase leads 1-2, 3-4	1, 2, 3, 4	4-lead generator sets are not reconnectable
	3	Three-phase leads 1-4, 2-5, 3-6, 7-10, 8-11, 9-12	1-12	12-lead generator sets are reconnectable to voltages shown on the generator set specification sheet
0 VCC		0	NEGRO Núm. 3	CC (-) Cable común de conexión a tierra. Requerido si el generador está apareado con un interruptor de transferencia de gestión de alimentación inteligente Generac.
12 V c.c.		194 – c.c. (+)	ROUGE no 4	Pour les commandes de transfert.
12 VCC		194	ROJO núm. 4	CC (+) para los controles de transferencia
12 VDC		194 (Red #4)	D	DC (+) 12 VDC for Transfer Controls
12 VDC		DC (+) 12 VDC for transfer controls	RED 194
12 VDC		DC (-) common ground wire	BLACK 0
12 VDC		Transfer control signal wire	WHITE 23	Required if generator is paired with optional Digital Power Management (DPM) smart technology
120	1	Battery charger AC input to generator backed-up 120VAC circuit	120VAC hot, neutral	Connect via wire nuts
120 V c.a.		T1	BLEU no 3	Avec fusible 120 V c.a. pour le chargeur de la batterie; doit être branché pour que la batterie demeure chargée.
120 VAC		Fused 120 VAC for battery charger	BLUE T1	Must be connected to keep battery charged whether unit is running or not
120 VAC		T1 (White #3)	B	Fused 120VAC for Battery Charger
120 VCA		T1	AZUL Núm. 3	Con fusible para el cargador de baterías (debe estar conectado para mantener la batería cargada, esté o no funcionando la unidad)
120/208	3	Wye		Voltage configuration (Figure 4-12)

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Common questions

What is the oil capacity of the Generac GT-999?

The Generac GT-999 engine has an oil capacity of 1.8 liters.

What is the displacement of the Generac GT-999?

The Generac GT-999 has a displacement of 0.999 liters with 2 cylinders.

Which generators use the Generac GT-999 engine?

The Generac GT-999 powers 4 generator set(s), including Generac 15 kW EcoGen, Generac 20 kW Synergy, Generac 8.1 GN, Generac G0070420.

How often should you change the oil in the Generac GT-999?

The Generac GT-999 oil change interval is every 500 hours.

What is a common problem with the Generac GT-999 engine?

A commonly reported issue on generators using the Generac GT-999 is: Unit will not start in AUTO with utility loss. Cause: Start delay countdown. Fix: If the start up delay is greater than expected, contact servicing dealer to adjust from 2 to 1500 seconds..