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Kohler Command PRO OHV CH20 Engine

The Kohler Command PRO OHV CH20 is a 624 L engine rated at 3600 rpm. It powers generator sets from Kohler, including the 8.5RES.

Also known as: KOHLER Command PRO OHV CH20

Part of the Kohler CH20 engine family — 5 variants share parts & fitment.

624.0 L

Displacement

3600 rpm

Rated speed

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

Engine specifications

Displacement	624.0 L
Rated speed	3600 rpm

Generator sets powered by this engine

Kohler 8.5RES

How to read your Kohler engine serial & model number →

Common problems

Stops suddenly
Cause: Fault shutdown
Fix: Check for a fault shutdown code on the controller’s LED display. Correct the fault and then move the generator set master switch to OFF/RESET to reset the controller.
Operates erratically
Cause: Air cleaner clogged
Fix: Replace element.
Lacks power
Cause: Air intake restriction, inadequate cooling
Fix: Inspect air intakes and exhaust for obstructions. Check air cleaner.
Generator set does not crank
Cause: Weak or dead battery
Fix: Recharge or replace battery. If battery is weak or dead, check battery charger fuse, power supply, and operation.
No output voltage
Cause: AC output circuit breaker open
Fix: Check for AC voltage on the generator side of circuit breaker. If there is AC voltage on the generator side of the breaker, then a problem in the load circuits is causing the line circuit breaker to trip. Check for and correct short circuits or overloading on the load side before resetting the circuit breaker.
Cranks but does not start
Cause: No fuel
Fix: Open (turn on) manual fuel valve. Check fuel supply tank (LP).
The generator set does not crank.
Cause: Battery weak or dead
Fix: Check power to the battery charger. Recharge or replace the battery.
Low output or excessive drop in voltage
Cause: Generator overloaded
Fix: Reduce load.
Generator set stops suddenly.
Cause: Low oil pressure shutdown
Fix: Check the oil level.
Starts hard
Cause: Low battery voltage
Fix: Check battery voltage and battery charger connections, power supply, and operation.
Controller LED display is off
Cause: No power to the controller: Continuous power mode jumper is disconnected and the generator set has not run for 48 hours or longer.
Fix: Controller display will automatically activate when a remote start command is received or the generator set master switch is moved to the RUN position. Connect the jumper to maintain continuous power to the controller, if desired. See Sections 2.3.6 and 6.9.3.
The generator set cranks but does not start, starts hard, lacks power, or operates erratically.
Cause: Air cleaner clogged
Fix: Clean and/or replace the air cleaner.
The generator set cranks but does not start, starts hard, lacks power, or operates erratically
Cause: Air cleaner clogged
Fix: Clean and/or replace the air cleaner.
The generator set cranks but does not start, starts hard, lacks power or operates erratically.
Cause: Air cleaner clogged
Fix: Clean and/or replace the air cleaner.
Generator set stops suddenly
Cause: Low oil pressure shutdown
Fix: Check the oil level. Check for signs of oil leaks.

Compiled from service & troubleshooting documentation across every generator set that uses the Kohler Command PRO OHV CH20.

Service intervals

Item	Action	Hours	Months	Notes
Oil level	Check	8 hr		First service — or before use
Air cleaner and precleaner	Clean	100 hr	12 mo	Yearly or 100 Hrs.; service more often in dusty areas
Air cleaner and precleaner (8.5/12RES)	Replace	100 hr	12 mo	Yearly or 100 hours; replace as necessary
Air cleaner and precleaner service	Clean	100 hr	12 mo	Yearly or 100 hr.; service more frequently in dusty areas
Air cleaner and precleaner service	Replace	100 hr	12 mo	Yearly or 100 hours, 8.5/12 kW models; replace as necessary
Air cleaner and precleaner service (8.5/12 kW)	Replace	100 hr		Yearly or 100 hours; service more frequently under dusty/dirty conditions
Change oil	Replace	100 hr	12 mo	Yearly or 100 hr.
Crankcase oil	Change	100 hr	12 mo	Yearly or 100 Hrs.
Engine oil	Change	100 hr	12 mo	Lubrication; Yearly or 100 hours
Oil cooler	Clean	100 hr	12 mo	Yearly or 100 hours; 17/18 kW models
Oil cooler	Inspect	100 hr		Yearly or 100 hours (17/18 kW models)
Oil cooler (17/18RES)	Clean	100 hr	12 mo	Yearly or 100 hours; inspect and clean
Air cleaner service	Clean	150 hr		Yearly or hours shown; 17/18 kW models
Air cleaner service	Replace	150 hr	12 mo	Yearly or 150 hours shown (300 hours also listed), 17/18 kW models
Air cleaner service (17/18 kW)	Replace	150 hr		Yearly or 150/300 hours
Change oil	Change	150 hr	12 mo	Yearly or 150 hours, 17/18 kW models
Engine oil (17/18RES)	Change	150 hr	12 mo	Yearly or 150 hours
Oil	Change	150 hr		Yearly or 150 hours; 17/18 kW models
Oil filter (17/18RES)	Replace	150 hr	12 mo	Yearly or 150 hours
Spark plugs	Clean	150 hr		Yearly or hours shown; 17/18 kW models
Spark plugs (17/18 kW)	Replace	150 hr		Yearly or 150/300 hours
Oil filter	Replace	200 hr	12 mo	Yearly or 200 hours; 8.5/12 kW models
Oil filter(s)	Replace	200 hr	12 mo	Yearly or 200 Hrs.
Replace filter	Replace	200 hr	12 mo	Yearly or 200 hours
Replace filter (oil filter)	Replace	200 hr		Yearly or 200 hours (8.5/12 kW models)
Replace filter(s)	Replace	200 hr	12 mo	Yearly or 200 hr.
Air cleaner service	Change	300 hr		Yearly or hours shown; 17/18 kW models
Spark plugs	Check	300 hr	12 mo	Yearly or 300 hours; 8.5/12 kW models
Spark plugs	Replace	500 hr	12 mo	Yearly or hours shown; 17/18 kW models
Spark plugs (8.5/12 kW)	Replace	300 hr		Yearly or 300 hours
Spark plugs (8.5/12RES)	Check	300 hr	12 mo	Yearly or 300 hours
Crankcase breather	Change	500 hr	12 mo	Lubrication; Yearly or 500 hours
Crankcase breather	Inspect	500 hr	12 mo	Yearly or 500 hours
Crankcase breather hose	Check	500 hr	12 mo	Yearly or 500 hours; 8.5/12 kW models
Crankcase breather hose	Clean	500 hr	12 mo
Crankcase breather hose	Inspect	500 hr		Yearly or 500 hours
Crankcase breather hose	Other	500 hr	12 mo	Yearly or 500 hr.; follow engine manufacturer's maintenance manual
Replace spark plugs	Replace	500 hr
Replace stepper motor coupling and bushing	Replace	500 hr		authorized distributor/dealer only
Resistance readings of windings with insulation tester (Megger)	Test	500 hr	36 mo	3 yr.; with SCR assembly or rectifier and load leads disconnected

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
Gap	Magnetic pickup air gap	0.5	mm (0.020 in.)
Gap	Spark Plug Gap 12/17/18RES	0.76	mm (0.030 in.)
Gap	Spark Plug Gap 8.5kW	0.51	mm (0.020 in.)
Gap	Spark plug gap	0.030	in.	cold
Gap	Spark plug gap	0.51	mm (0.02 in.)
Gap	Spark plug gap	0.7--0.8	mm (0.028--0.030 in.)
Gap	Spark plug gap	0.76	mm (0.030 in.)
Gap	Spark plug gap	0.8--0.9	mm (0.03--0.04 in.)
Gap	Spark plug gap	0.89	mm (0.035 in.)
Gap	Spark plug gap	0.9--1.0	mm (0.036--0.04 in.)
Gap	Spark plug gap, 12/17/18RES	0.76	mm (0.030 in.)	cold
Gap	Spark plug gap, 8.5 kW	0.51	mm (0.020 in.)	cold
Other	Battery electrolyte specific gravity	1.260	specific gravity	at 26.7 C (80 F), full charge
Other	Battery electrolyte specific gravity (full charge)	1.260		electrolyte at 26.7 C (80 F)
Other	Battery electrolyte specific gravity minimum	1.215	specific gravity	at 26.7 C (80 F); recharge if less
Other	Battery specific gravity (charge threshold)	1.215		electrolyte at 26.7 C (80 F)
Other	Battery specific gravity variation (charge threshold)	0.01		cell-to-cell variation
Other	Brush length, new	19.05	mm (0.75 in.)	new
Other	Compression ratio	8.5:1
Other	Compression ratio	9.0:1
Other	Fuel system leak test pressure	6-8 ounces per square inch (10-14 inches water column)	oz/in²	LPG vapor or natural gas system
Other	Insulation resistance indicating good stator/rotor	500	kOhms (1/2 megohm) or higher
Other	Megohmmeter test voltage (stator/rotor to ground)	500	VDC
Other	No load and full load frequency tolerance	0.4	Hz	rated generator frequency
Other	Overfrequency shutdown	110	% of system frequency setpoint for more than 5 seconds	10 second inhibit after start
Other	Overfrequency shutdown threshold	110	% of system frequency setpoint	more than 5 seconds, active 10s after start
Other	Underfrequency shutdown	90	% of nominal system frequency for more than 5 seconds	10 second inhibit after start
Other	Underfrequency shutdown threshold	54	Hz	more than 5 seconds (or below 56.5 Hz for more than 60 seconds)
Pressure	Engine oil pressure	172--241	kPa (25--35 psi)
Pressure	Fuel regulator inlet gas pressure	7-11	in. (4-6 oz.)	at fuel regulator inlet
Pressure	Fuel supply pressure	1.7--2.7	kPa	(7-11 in. H2O)
Pressure	Fuel supply pressure	1.7-2.7	kPa	natural gas or LP vapor
Pressure	Fuel supply pressure	7-11	in. H2O	natural gas or LP vapor
Pressure	Fuel supply pressure at secondary regulator inlet	178--280	mm water column (7--11 in. H2O) or 1.7--2.7 kPa (4--6 oz./in.2)	generator set running at rated load
Pressure	Fuel system leak test (LP vapor or natural gas)	6--8 ounces per square inch (10--14 inches water column)	oz/in2	system pressurized, soap and water solution
Pressure	Gas fuel system leak test pressure	6--8	oz/in2	(10-14 inches water column), soap and water solution
Pressure	Gas fuel system leak test pressure	6-8	oz/in2	10-14 in. water column
Pressure	LP supply pressure	1.7--2.7	kPa (7--11 in. water column)
Pressure	Low oil pressure shutdown	24.1	kPa ±13.8 kPa (3.5 psi ±1.5 psi)
Pressure	Low oil pressure shutdown	24.1 ±13.8	kPa	shutdown threshold
Pressure	Low oil pressure shutdown	3.5 ±1.5	psi	shutdown threshold
Pressure	Natural gas supply pressure	1.2--2.7	kPa (5--11 in. water column)
Pressure	Secondary regulator maximum inlet pressure	2.7	kPa (6 oz./in.2) or 280 mm (11 in.) water column
Resistance	Brush resistance	0.1--0.2	ohms (without meter lead resistance)
Resistance	Coolant temperature sensor (CTS) resistance	180--200	ohms	at 100 C (212 F)
Resistance	Coolant temperature sensor (CTS) resistance	2100--2500	ohms	at 30 C (86 F)
Resistance	Coolant temperature sensor resistance at 100 C (212 F)	180--200	ohms	100 C
Resistance	Coolant temperature sensor resistance at 30 C (86 F)	2100--2500	ohms	30 C
Resistance	Magnetic pickup resistance across QCON1 and QCON2	1.3--1.9	kOhm
Resistance	Resistance through the brushes	0.1--0.2	ohms	without meter lead resistance
Resistance	Rotor resistance	4.0	ohms, cold	cold
Resistance	Rotor resistance	4.2	ohms, cold	cold
Resistance	Rotor resistance, cold	4.0	ohms	cold
Resistance	Starter relay coil resistance	5--7	ohms
Resistance	Stator resistance leads 1-2, 3-4	0.07	ohms, cold	cold
Resistance	Stator resistance leads 1-4, 2-5, 3-6, 7-10, 8-11, 9-12	0.18	ohms, cold	cold
Resistance	Stator resistance leads 11-44	0.14	ohms, cold	cold
Resistance	Stator resistance leads 55-66	0.15	ohms, cold	cold
Resistance	Stator resistance leads 55-66	0.70	ohms, cold	cold
Resistance	Stator resistance, leads 1-2, 3-4	0.07	ohms	cold

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	Ambient	Capacity	Notes
Engine oil	5W-30	API SG, SH, or SJ synthetic			Synthetic oil recommended
Engine oil	API Service Class SG, SH, or SJ synthetic oil	API SG/SH/SJ		1.9 L	Select viscosity based on air temperature; Figure 3-2 shows 10W-30 and 5W-20/5W-30.
Engine oil	Synthetic oil, API Service Class SG or higher	API SG or higher		1.9 L (2.0 qt.)	8.5RES capacity with filter; see engine oil selection chart for viscosity (5W-20, 5W-30, 10W-30)
Engine oil	5W-20, 5W-30	API Service Class SG or higher, synthetic	-30°C to 10°C		Engine Oil Selection chart; use synthetic oil
Engine oil	10W-30	API Service Class SG or higher, synthetic	-20°C to 40°C		Engine Oil Selection chart; use synthetic oil
Fuel		LP gas or natural gas			Minimum supply pressure 7--11 in. H2O (4--6 oz./in.2); multi-fuel system field convertible
Fuel	LP gas or natural gas				LP/natural gas minimum supply pressure 7--11 in. H2O (4--6 oz./in.2)
Fuel	LP vapor				Nominal fuel rating 2500 Btu/ft3 (93 MJ/m3); supply pressure 1.7--2.7 kPa (7-11 in. H2O); LP vapor conversion factors: 8.58 ft3 = 1 lb., 36.39 ft3 = 1 gal.
Fuel	LPG				Fuel supply pressure 1.7-2.7 kPa (7-11 in H2O); nominal fuel rating 2500 Btu/ft3 (93 MJ/m3); supply inlet 1/2 NPT
Fuel	Natural Gas				Fuel supply pressure 1.3-2.7 kPa (5-11 in H2O) for 8.5/12RES, 1.7-2.7 kPa (7-11 in H2O) for 18RES; nominal fuel rating 1000 Btu/ft3 (37 MJ/m3); supply inlet 1/2 NPT
Fuel	Natural Gas or LP Vapor	Nominal fuel rating: natural gas 37 MJ/m3 (1000 Btu/ft3); LP vapor 93 MJ/m3 (2500 Btu/ft3)			Fuel supply inlet 1/2 NPT; supply pressure natural gas 1.2-2.7 kPa (5-11 in. H2O), LP 1.7-2.7 kPa (7-11 in. H2O)
Fuel	Natural gas				Nominal fuel rating 1000 Btu/ft3 (37 MJ/m3); supply inlet 1/2 NPT; supply pressure 1.7--2.7 kPa (7-11 in. H2O)
Fuel	Natural gas or LP vapor				Nominal fuel rating: natural gas 1000 Btu/ft3 (37 MJ/m3); LP vapor 2500 Btu/ft3 (93 MJ/m3). Supply pressure 1.7-2.7 kPa (7-11 in. H2O).
Fuel	Natural gas or propane (LP) vapor	Field-convertible multi-fuel; CARB emission certified			Clean-burning natural gas or propane (LP) vapor; air-cooled engine, no liquid coolant
Fuel	natural gas or propane (LP) vapor				Field-convertible multi-fuel system maintaining CARB emission certification
Other	Bicarbonate of soda (baking soda) and water solution				Battery acid cleanup: 500 g (1 lb.) bicarbonate of soda to 4 L (1 gal.) water; also used to clean battery and cables
Other	Petroleum jelly, silicone grease, or other nonconductive grease				Coat battery terminals after reconnecting cables

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
AF	Auxiliary fault input shutdown	Shutdown initiated by pushing the emergency stop switch (TRES models only). Not used on RES models.	Shutdown	Check the position of the emergency stop button (TRES models only).
CC	Crank cycle
CO-3		Fault displayed if the CO parameter is set incorrectly	Shutdown
CO-6		Fault displayed if the CO parameter is set incorrectly	Shutdown
HB	High battery voltage warning	Displayed if engine starting battery voltage rises above 16 VDC for more than 30 seconds when engine is running.	Warning	Check the battery rating and condition; check battery charger operation.
HE	High engine temperature shutdown	Shutdown occurs if the engine coolant temperature exceeds the maximum for more than 5 seconds. Active after engine reaches crank disconnect speed.	Shutdown	Check for blocked air inlets and exhaust outlets.
LB	Low battery voltage warning	Displayed if engine starting battery voltage falls below 11 VDC for more than 30 seconds when engine is not running.	Warning	Check the battery rating and condition; check battery charger operation; charge or replace battery.
LCL	Low coolant level	Not used on air-cooled models	Shutdown
LOC	Loss of coolant	Not used on air-cooled models	Shutdown
LOP	Low oil pressure shutdown	Shutdown occurs if a low oil pressure condition exists for more than 5 seconds. Active 30 seconds after crank disconnect speed.	Shutdown	Check for leaks in lubrication system; check oil level and add oil if low.
OC	Overcrank shutdown	Shutdown after 3 unsuccessful starting attempts (15s crank, 15s rest each). Also on locked rotor if no engine rotation sensed during cranking.	Shutdown	Check fuel supply, spark plug, battery, loose connections. Contact dealer if problem continues.
OF	Overfrequency shutdown	Shutdown occurs when governed frequency exceeds 110% of system frequency setpoint for more than 5 seconds. Active 10 seconds after engine start.	Shutdown	Contact an authorized distributor/dealer for service if problem continues.
OS	Overspeed shutdown	Shutdown occurs if engine speed exceeds 110% of normal running speed for more than 0.3 seconds.	Shutdown	Contact an authorized distributor/dealer for service if problem continues.
OU	Overvoltage shutdown	Shutdown occurs if voltage exceeds 120% of system nominal voltage for more than 2 seconds.	Shutdown	Contact an authorized distributor/dealer for service if problem continues.
SCF0	Software Communication Fault 0	Indicates a software or communication problem within the controller.	Shutdown	Replace the controller.
UF	Underfrequency shutdown	Shutdown occurs if governed frequency falls below 54 Hz for more than 5 seconds, or below 56.5 Hz for more than 60 seconds. Active 10 seconds after engine start.	Shutdown	Reduce load and restart; contact dealer if problem continues.
UU	Undervoltage shutdown	Shutdown occurs if voltage falls below 80% of nominal system voltage for more than 10 seconds.	Shutdown	Reduce load and restart; contact dealer if problem continues.

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

Procedures

ADC-RES Controller Configuration (Cn setting) adjustment

⚠ The controller automatically exits configuration mode without saving changes after about 1 minute if no buttons are pressed.

Enter the configuration mode while the engine is not running by following the Figure 26 sequence.
Step through the parameters to the communication setting Cn parameter.
Use the up and down arrow buttons to change the Cn setting to Cn01, if necessary.
Press to SAVE CHANGES (YES) before exiting the configuration mode.
Move the generator set master switch to OFF/RESET.

Controller Configuration adjustment

⚠ Be sure to save the new settings immediately before exiting the configuration mode; changes are lost if the controller times out (about 1 minute).

Hold the Select button and move the master switch to RUN to enter configuration mode.
Press the down arrow key then the up arrow key 3 times to enter configuration mode (password).
Set the voltage/frequency parameter Uu for the model.
Set the unit configuration parameter Uc (marine, standby, mobile).
Set the engine type parameter Ec.
Press the up arrow at the Adnc display to enter advanced configuration mode.
Set the engine data input type Ed.
Set the battery voltage Bt (12 or 24 VDC).
Set the communications parameter Cn.
Enter save mode and save your settings before exiting.

Frequency Adjustment Procedure adjustment

⚠ Hazardous voltage. Operate the generator set only when all guards and electrical enclosures are in place.

Tools: frequency meter

Open the generator set line circuit breaker.
Attach a frequency meter to the AC output leads.
Start and run the generator set until normal operating temperature (at least 10 minutes).
Use the ADC controller to adjust the electronic governor speed (parameter 4P) for 60 Hz (or 50 Hz).
Check stability with no load; decrease gain (parameter 5P) until stable if speed hunts or surges.
Repeat steps 4 and 5 to obtain rated frequency and stable operation.
Save the settings.
Apply rated load and observe frequency; no load and full load frequencies should be within 0.4 Hz of rated.
Check for hunting and surging at full load; increase gain until engine hunts, then decrease in small steps.
Remove the load and observe frequency; repeat step 4 if frequency changed.

Fuel Conversion Procedure (Models with Fuel Block) adjustment

⚠ Explosive fuel vapors. Use extreme care when handling, storing, and using fuels.

Disable genset: master switch OFF, disconnect battery charger, disconnect battery negative lead first.
Turn off fuel supply.
Remove hose clamp and fuel hose from hose fitting in the fuel metering valve.
Remove hose fitting from the natural gas outlet port.
Remove plug from LP port; clean, apply pipe sealant, install plug into natural gas port.
Clean hose fitting, apply pipe sealant, install fitting into LP port.
Slide hose onto fitting and secure with clamp.
For 12 kW models: connect DSAI leads together for natural gas (disconnect for LP).
Connect and turn on new fuel supply; reconnect battery negative last; reconnect battery charger.
Start genset and check for leaks using a gas leak detector.

Fuel Conversion Procedure (natural gas to LP vapor) adjustment

⚠ Do not adjust the factory-sealed fuel-metering adjustments on the fuel block.

⚠ Explosive fuel vapors can cause severe injury or death.

⚠ Accidental starting can cause severe injury or death.

Tools: Gas leak detector

Place the master switch in OFF, disconnect battery charger power, disconnect battery (negative lead first), and turn off fuel supply.
Remove the hose clamp and fuel hose from the hose fitting in the fuel block.
Remove the hose fitting from the natural gas outlet port in the fuel block.
Remove the plug from the LP port, clean it, apply fresh pipe sealant, and install it into the natural gas outlet port.
Clean the hose fitting, apply fresh pipe sealant to the threads, and install it into the LP port.
Slide the hose onto the fitting and secure it with the clamp.
For 12RES only: connect the DSAM leads together for natural gas (disconnect for LP vapor).
Connect and turn on the new fuel supply; recheck the master switch is OFF.
Reconnect the battery (negative lead last) and reconnect battery charger power.
Start the generator set by moving the master switch to RUN and check for leaks with a gas leak detector.
Move the generator set master switch to the AUTO position.

Fuel Metering Valve Adjustment Procedure adjustment

⚠ Adjusting fuel metering valves on emission-certified gensets may void the emission certification. Only trained authorized technicians may adjust.

Tools: Digital voltmeter (DVM), UEGO oxygen sensor service kit GM29385, Load bank

Disable genset (master switch OFF, disconnect battery charger).
Remove oxygen sensor plug from exhaust manifold and install oxygen sensor.
Connect oxygen sensor to engine starting battery, control module, and voltmeter.
Reconnect battery charger, start genset, and run to normal operating temperature.
Apply rated load; measure oxygen sensor output voltage (potential to ground).
Adjust fuel metering valve to obtain specified oxygen sensor output.
Seal metering valve adjustment screws with thread sealant.
Remove load and cool genset 5-10 minutes; stop genset.
Disconnect battery negative lead first; allow exhaust to cool.
Remove oxygen sensor and reinstall exhaust plug with antiseize; reconnect battery negative lead last and battery charger.

Mechanical Governor Arm Adjustment Procedure adjustment

⚠ Accidental starting can cause severe injury or death.

Tools: Nail

Make sure throttle linkage is connected to governor arm and carburetor throttle lever.
Loosen the hex nut holding the governor lever to the cross shaft.
Move governor lever toward carburetor as far as it will go (wide open throttle) and hold.
Insert a nail into the hole in the cross shaft and rotate the shaft counterclockwise as far as it will turn; tighten hex nut and remove nail.

Output Voltage and Frequency Adjustment adjustment

⚠ The generator set must be running during these adjustments.

⚠ The engine speed (frequency) adjustment menus are not accessible on models with mechanical governors.

Tools: multimeter

Move the master switch to RUN; the engine starts and runtime hours display.
Hold the Select button about 5 seconds until the program version number displays.
Press the down arrow key then the up arrow key 3 times to enter adjustment mode.
1P: adjust voltage coarse in large increments (approximately 5-7 volts per step).
2P: adjust voltage fine in smaller increments (approximately 0.5-0.7 volts per step).
Adjust voltage stability (gain) coarse and fine.
3P: set volts/Hz (00=low, 09=high).
4P: adjust engine governor speed coarse and fine.
5P: adjust engine governor stability (gain) coarse and fine.
Enter SAVE mode and save settings before exiting the adjustment mode.

Spark Plug Gap Adjustment adjustment

Tools: wire feeler gauge

Clean area around spark plug base.
Remove spark plug and inspect condition.
Replace plug if worn or reuse is questionable.
Check gap with wire feeler gauge.
Adjust gap to 0.76 mm (0.030 in.) by bending ground electrode.
Reinstall spark plug.

Voltage Adjustment Procedure adjustment

⚠ Hazardous voltage. Operate the generator set only when all guards and electrical enclosures are in place.

Tools: digital voltmeter, frequency meter

Connect a digital voltmeter from one side of the circuit breaker to the L0 terminal inside the controller assembly.
Start the generator set.
Enter the adjustment mode and increase or decrease voltage (parameter 1P) to the desired voltage.
Adjust the voltage gain (parameter 2P) until light flicker minimizes; save settings.
Check and readjust the voltage if necessary.
Set voltmeter to frequency; adjust engine governor speed (parameter 4P) to the cut-in frequency.
Set voltmeter to voltage; adjust volts/Hz (parameter 3P) until voltage begins to drop.
Set voltmeter to frequency; adjust engine governor speed (parameter 4P) to the operating frequency (50 or 60 Hz).
Readjust voltage gain (parameter 2P) until light flicker minimizes.
Check voltage; readjust voltage (parameter 1P) if necessary.
Save the settings.
Stop the generator set.

Governor System Operation Test Procedure diagnostic

⚠ Hazardous voltage. Operate the generator set only when all guards and electrical enclosures are in place.

Tools: voltmeter, feeler gauge

Verify carburetor throttle linkage is connected to the stepper motor.
Look for broken or loose wiring or plug connections if stepper motor moves erratically.
Check stepper motor operation at startup; note throttle positions.
If throttle moves fully open then steps to and stays fully closed, check the magnetic pickup.
Connect a voltmeter to the magnetic pickup leads; check for 1.75 volts AC minimum during cranking.
If below 1.75 VAC, verify magnetic pickup air gap is 0.5 mm (0.020 in.); adjust as needed.
After adjusting gap, recheck voltage; replace magnetic pickup if still below 1.75 VAC.
Disconnect magnetic pickup leads and open circuit breaker to test controller governing function.
Move throttle shaft/stepper motor fully counterclockwise (closed throttle).
Start the generator set; stepper motor should step clockwise to wide open throttle and remain there.
Place master switch in STOP; check stepper motor connections (leads 1A, 1B, 2A, 2B to P1-4, P1-5, P1-6, P1-7).
Check stepper motor coil resistance across pins 2 and 3 and across pins 1 and 4.

Network Bridge Diagnostics diagnostic

Check the network LEDs on the RJ45 connector for Ethernet network communication.
Check the STAT LED; if not lit, check connections and the engine starting battery.
Check the TX and RX LEDs for CAN data transmission and reception.
If neither the TX nor the RX LED flashes, check bridge power, connections, and settings.
If only one of the TX or RX LEDs flashes, check the connected devices on the generator set (CAN) side.

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
		Continuous power mode jumper	P7 pins 1 and 2	Remove for power-down; connect pins 2 and 3 for storage if three-pin connector.
		Remote start	Controller leads 3 and 4	Connect leads 3 and 4 from the ADC 2100 controller to the ATS engine start terminals or a remote start/stop switch.
		Remote start/stop	3 and 4	Connect to ATS engine start terminals or remote start/stop switch.
	single	AC output to line circuit breaker	L1/L2 black	Connect to AC circuit breaker load side.
	single	Equipment ground	green	Connect to equipment ground terminal labeled GRD.
	single	Neutral	L0 white	Connect ATS and main panel L0 leads to neutral terminal.
	single phase	AC output leads to AC circuit breaker	L1/L2 (black)	Connect output leads going to the transfer switch to the AC circuit breaker load side; route through flexible conduit to circuit breaker box.
	single phase	Equipment ground	Green	Connect the green lead to the equipment ground terminal (labeled GRD).
	single phase	Neutral	L0 (white)	Connect the L0 white leads from the ATS and the main panel to the neutral terminal.
100 VAC	1	1Ph, 2W		Uu00; 60 Hz
100 VAC	1	1Ph, 3W		Uu00; 60 Hz
100/200 VAC	1	1Ph, 3W		Uu08; 60 Hz
110	Single (L0-L1)	Factory two-pole circuit breaker		50 Hz; not reconnectable
110	Single (L0-L2)	Factory two-pole circuit breaker		50 Hz; not reconnectable
110 VAC	1	1Ph, 2W		Uu05; 50 Hz
110 VAC	1	1Ph, 3W		Uu05; 50 Hz
110 volt	1	L0-L1		50 Hz; 3-wire configuration; 8.5/12RES not reconnectable
110 volt	1	L0-L2		50 Hz; 3-wire configuration; 8.5/12RES not reconnectable
110/190 VAC	3	Wye		Uu17; 50 Hz
110/220 VAC	1	1Ph, 3W		Uu07; 50 Hz
110/220 VAC	1	Dogleg		Uu07; 50 Hz
110/220 VAC	3	Delta		Uu15; 50 Hz
115 VAC	1	1Ph, 2W		Uu05; 50 Hz
115/200 VAC	3	Wye		Uu23; 50 Hz
115/230	1	Output reconnectable	4	50 Hz models
115/230 VAC	1	1Ph, 3W		Uu02; 50 Hz
115/230 VAC	1	Dogleg		Uu06; 50 Hz
115/230 VAC	3	Delta		Uu14; 50 Hz
12		Engine starting battery	Positive (+) and negative (--)	12-volt engine electrical system, negative ground. Positive lead to starter solenoid; negative lead to ground terminal on or near starter motor.
120	Single (L0-L1)	Factory two-pole circuit breaker; 4 stator leads	1, 2, 3, 4 (output); 11, 44, 55, 66 (sensing/supply)	60 Hz, 110/220 and 120/240 V, 3-wire configuration; not reconnectable

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

Parts cataloged across the Kohler CH20 family

Part #	Description	Category
24 083 02	Precleaner element	Air filter
24 083 02-S	Precleaner	Air filter
24 083 05-S	Precleaner	Air filter
24 083 08	Air cleaner element	Air filter
24 083 08-S	Element, air filter	Air filter
24 083 09-S	Element, air filter	Air filter
ADV-6823-A	Air Filter, Spark Plug Location	Air filter
269373	Alternator Assembly	Alternator
EZ-273000-J	Battery Connection	Battery
25 158 08-S	Bushing, linkage retaining	Bushing
GM29253-GA1	Controller Wiring Diagram	Controller wiring diagram
GM29253-GA2	Controller Wiring Diagram	Controller wiring diagram
24 050 01-S	Filter, breather	Filter
745-020-B0-003	Enclosure Grounding Stud	Grounding stud
345079	Relay (being replaced by GM50772)	Kit
12 050 01	Oil Filter	Oil filter
12 050 01-S	Filter, oil	Oil filter
042-146-10	Low pressure Excess Flow Valve (above ground ¾” x 4” NPT nipple)	Service part / kit
223316	Fuse, 10 A, 250 V	Service part / kit
24 079 09-S	Bushing, linkage	Service part / kit
24 310 03-S	Governor (actuator/stepper motor)	Service part / kit
25 112 09-S	Spacer	Service part / kit
292937	Fuse, 20 A, 250 V	Service part / kit
345095	Annual Maintenance Kit	Service part / kit
358337	Fuse: Auxiliary Winding (F1) 10 Amp	Service part / kit
358359	Coupling, stepper motor	Service part / kit
358384	Circuit breaker	Service part / kit
745-020-B0-001	Rev. A.	Service part / kit
A-345233	Lead	Service part / kit
AGS-10	AGS 10 inline fuse, battery charger (located in the battery lead)	Service part / kit
F-228605	Kit, voltage regulator	Service part / kit
GM10064	PCB assembly (relay controller)	Service part / kit
GM19462-KP4-QS	Carburetor heater kit	Service part / kit
GM24928	Circuit breaker	Service part / kit
GM29671	PCB Assy., Relay board 12V	Service part / kit
GM48784	Battery, 12 volt wet-charged, BCI group size 26, 525 CCA at -18 C, 70 min. reserve capacity	Service part / kit
GM48808-KP1	Battery kit, wet-charged, contains 1 battery, BCI group size 26, 525 CCA, 70 min. reserve capacity	Service part / kit
GM49746	Relay, 12 VDC	Service part / kit
GM58703	Assy, J1939/ModBus/Ethernet Converter (network bridge)	Service part / kit
GM62345	Maintenance Service Kit	Service part / kit
GM62345-SKP1-QS	Maintenance Kit	Service part / kit
GM62346-SKP1-QS	Maintenance Kit	Service part / kit
GM62347-SKP1-QS	Maintenance Kit	Service part / kit
GM90365-SKP1-QS	Maintenance Kit	Service part / kit
GM90366-SKP1-QS	Maintenance Kit	Service part / kit
GM29358-B	Point-to-Point Wiring Diagram, Single Phase	Point-to-point wiring diagram
X-6422-31	Seal	Seal
241927	Sensor, speed	Sensor
A-345052	Engine oxygen sensor	Sensor
GM28823	Sensor, oil temperature	Sensor
GM28981	UEGO sensor interface harness	Sensor
GM29385	UEGO oxygen sensor service kit	Sensor
12 132 02	Spark plug	Spark plug
12 132 02-S	Spark Plug	Spark plug
24 132 01	Spark Plug	Spark plug
25 132 14-S	Spark plug	Spark plug
BKR-8YU11	Spark Plug, CH20/CH740	Spark plug
GM50772	Starter Relay Service Kit	Starter

Parts cataloged across all variants of this engine family — verify the exact part fits your specific variant and serial number before ordering.

Common questions

What is the displacement of the Kohler Command PRO OHV CH20?

The Kohler Command PRO OHV CH20 has a displacement of 624.0 liters.

Which generators use the Kohler Command PRO OHV CH20 engine?

The Kohler Command PRO OHV CH20 powers 1 generator set(s), including Kohler 8.5RES.

What is a common problem with the Kohler Command PRO OHV CH20 engine?

A commonly reported issue on generators using the Kohler Command PRO OHV CH20 is: Stops suddenly. Cause: Fault shutdown. Fix: Check for a fault shutdown code on the controller’s LED display. Correct the fault and then move the generator set master switch to OFF/RESET to reset the controller..