Generac MIH1.2 troubleshooting: 42 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Generac MIH1.2 — full specs, parts & maintenance.
| Symptom | Cause | Remedy |
|---|---|---|
| Engine does not crank | Low battery output voltage or discharged battery. Loose or corroded connections. Faulty start circuit relay. Blown fuse. Faulty main switch or start safety switch. Faulty starter solenoid. Faulty starter. | Charge or replace batteries. See Battery Inspection. Clean and tighten connections. Contact a GMASD. Replace fuse. Repair switch as required. Replace solenoid. Replace starter. |
| Starter cranks slowly | Low battery output voltage or discharged battery. Excessive crankcase oil viscosity. | Charge or replace batteries. See Battery Inspection. Drain crankcase oil and replace with correct viscosity oil. See Draining and Refilling the Oil. |
| Hard to start, or does not start | Engine starting under load. Incorrect starting procedure. Restricted exhaust. No fuel. Air in fuel line. Poor fuel quality. Water, dirt, or air in fuel system. Fuel filter restricted or full of water. Dirty or faulty fuel injectors. Electronic fuel system failure. Cold weather. | Disengage PTO. Review starting procedure. See Pre-start Checklist and Engine and Heater Startup. Inspect and correct exhaust restriction. Check fuel tank. Purge fuel lines. See engine manual. Drain fuel and replace with proper grade and quality of fuel for operating condition. Drain, flush, fill, and purge fuel system. Replace fuel filter or drain water from fuel filter. Contact a GMASD. Use cold weather starting aids (see engine manual). |
| Engine misfiring or runs irregularly | Poor fuel quality; incorrect fuel/dirty fuel. Restricted fuel filter. Water, dirt, or air in fuel system. | Test fuel, drain water from fuel bowl. Replace fuel filter element. Drain, flush, fill, and purge fuel system. |
| Lack of engine power | Restricted air intake. Restricted exhaust. Poor fuel quality. Restricted fuel filter. Engine overloaded. Incorrect crankcase oil. Low coolant temperature. Incorrect valve clearance. Dirty or faulty fuel injectors. Air leak in engine intake or exhaust manifold. | Service air cleaner. Check and correct exhaust restriction. Drain fuel and replace with proper grade and quality of fuel for operating condition. Replace fuel filter elements. Reduce engine load. Drain crankcase oil and replace with correct viscosity oil. See Draining and Refilling the Oil. Remove and check thermostat. Adjust valve clearance or contact a GMASD. Check intake and exhaust manifold gaskets and manifolds; repair as required or contact a GMASD. |
| Engine idles poorly | Poor fuel quality. Electronic control system problem or basic engine problem. | Drain fuel and replace with proper grade and quality of fuel for operating condition. Contact a GMASD. |
| Excessive fuel consumption | Engine overloaded. Restricted or dirty air cleaner. Insufficient compression.Leaks in fuel supply system. Poor fuel quality/improper type of fuel. Incorrect valve clearance. Dirty or faulty fuel injectors. Electronic fuel system failure. | Reduce engine load. Replace air cleaner element as required. Determine cause of low compression and repair as required. Locate source of leak and repair as required. Drain fuel and replace with proper grade and quality of fuel for operating condition. Adjust valve clearance or contact a GMASD. Contact a GMASD. |
| Engine emits white smoke | Insufficient engine compression. Faulty thermostat(s) (does not close). Coolant entering combustion chamber (failed cylinder head gasket or cracked cylinder head). | Determine cause of low compression and repair as required, or contact a GMASD. Test thermostats; replace thermostats as required. Repair or replace as required, or contact a GMASD. |
| Engine emits black, gray, or blue smoke | Restricted or dirty air cleaner; Incorrect type of fuel | Replace air cleaner element as required; Drain fuel and replace with proper grade, type, and quality of fuel for operating condition |
| Engine burning oil | Contact a GMASD | |
| Electronic control system problem or basic engine problem | Contact a GMASD | |
| Cracked or damaged exhaust filter | Contact a GMASD | |
| Engine overheats | Restricted or dirty air cleaner; Insufficient coolant in cooling system; Incorrect grade of fuel | Replace air cleaner element as required; Fill cooling system to proper level. Check radiator and hoses for loose connections or leaks; Drain fuel and replace with proper grade, type, and quality of fuel for operating condition |
| Insufficient engine oil | Check oil level. Add oil as required. See Draining and Refilling the Oil | |
| Dirty radiator core | Clean cooling system as required | |
| Cooling system needs flushing | Flush coolant system | |
| Engine overloaded | Reduce engine load | |
| Loose or faulty fan belt | Check automatic belt tensioner and belts. Replace as required | |
| Faulty or wrong type of thermostat(s) | Test thermostat opening temperature, replace thermostats as required | |
| Faulty radiator cap | Replace radiator cap as required | |
| Faulty temperature gauge or temperature sender | Check gauge, sender, and connections | |
| Damaged or leaking cylinder head gasket | Contact a GMASD | |
| Faulty coolant pump | Coolant temperature below normal; Test and replace thermostats as required | |
| Faulty thermostat(s) | Test and replace thermostats as required | |
| Coolant in crankcase | Faulty cylinder head gasket | Contact a GMASD |
| Cracked cylinder head or block; Leaking cylinder liner seals; Pitted cylinder liners; Leaking oil cooler; Faulty oil cooler O-rings; Leaking EGR cooler system; Faulty coolant pump seal; weep hole plugged; coolant leaking through bearing | Contact a GMASD | |
| Excessive oil consumption | Insufficient crankcase oil viscosity | Drain crankcase and refill with correct viscosity oil. See Draining and Refilling the Oil |
| Excessive crankcase oil | Drain oil until oil level is correct. See Draining and Refilling the Oil | |
| External oil leak(s) | Determine source of oil leak(s) and repair as required | |
| Restricted crankcase vent tube | Clean vent tube, verify that crankcase oil level is correct | |
| Excessive oil pressure | Contact a GMASD | |
| Worn, broken, or unseated oil control rings; Scored cylinder liners or pistons; Worn valve guides or stems; Faulty turbocharger; Front and/or rear crankshaft oil seal faulty | Contact a GMASD | |
| Piston ring gaps not staggered; Insufficient piston ring tension; Piston rings sticking in ring grooves; Piston ring grooves excessively worn | Contact a GMASD | |
| Batteries will not charge | Loose or corroded connections; Sulfated or worn-out batteries | Clean and tighten connections; Replace batteries. See Battery Installation and Replacement |
| Stretched belt or faulty belt tensioner | Adjust belt tension or replace belts | |
| Entire electrical system does not function | Faulty battery connection; Sulfated or worn-out batteries | Clean and tighten connections; Replace batteries. See Battery Installation and Replacement |
| Blown fuse | Replace fuse | |
| Generator overheating | Overloaded generator; Clogged ventilation screens; High altitude; Insufficient air circulation; Unbalanced load | Reduce load; Remove debris and clean air passages; Reduce load or improve ventilation. Contact a GMASD; Contact a GMASD; Abnormal generator noises |
| Abnormal generator noises | Faulty bearing; Loose or misaligned coupling; Belt slap or loose guards | Contact a GMASD |
| Thermostat not functioning | Incorrect wiring; Incorrect sensor operation | Contact a GMASD |
| Display shows fault code | See thermostat manual, or contact a GMASD | |
| No heat | Burner malfunction | Contact a GMASD |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Low battery output voltage or discharged battery. Loose or corroded connections. Faulty start circuit relay. Blown fuse. Faulty main switch or start safety switch. Faulty starter solenoid. Faulty starter.. See the table for the matching fixes.
Documented causes: Low battery output voltage or discharged battery. Excessive crankcase oil viscosity.. See the table for the matching fixes.
Documented causes: Engine starting under load. Incorrect starting procedure. Restricted exhaust. No fuel. Air in fuel line. Poor fuel quality. Water, dirt, or air in fuel system. Fuel filter restricted or full of water. Dirty or faulty fuel injectors. Electronic fuel system failure. Cold weather.. See the table for the matching fixes.