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Home›Engines›Kohler CH-74

Kohler CH-74 Engine

The Kohler CH-74 is an engine rated at 2900 rpm. It powers generator sets from Kohler, including the 6VSG-24V, 6VSG-36V and 6VSG-48V.

Also known as: CH-74, Kohler CH-74

2900 rpm
Rated speed
On this pageSpecsGenerator setsFAQProceduresWiring

Engine specifications

Rated speed2900 rpm

Generator sets powered by this engine

3
Kohler 6VSG-24VKohler 6VSG-36VKohler 6VSG-48V

How to read your Kohler engine serial & model number →

Common problems

15
  • Stops suddenly
    Cause: Fault shutdown
    Fix: Check for a fault shutdown message on the controller display; Identify the cause of the fault; Correct the fault and then press the controller's OFF button to reset the controller
  • Lacks power
    Cause: Air intake restriction, inadequate cooling
    Fix: Inspect air intakes and exhaust for obstructions; Check air cleaner; Clear air intakes and exhaust area; Maintain clearances shown on the genset dimension drawing; Replace air cleaner element
  • Cranks but does not start
    Cause: No fuel
    Fix: Verify that manual fuel valve is open; Check fuel supply tank (LPG); Open (turn on) manual fuel valve; Contact fuel supplier to add fuel to fuel supply tank (LPG).
  • Starts hard
    Cause: Low battery voltage
    Fix: Check battery voltage during cranking; Charge battery; Replace battery if necessary; Check battery charger connections and power connection to the generator set; Tighten loose connections.
  • Low output or excessive drop in voltage
    Cause: Generator overloaded
    Fix: Reduce electrical load and check operation; Unplug some lights or appliances connected to the generator set
  • Erratic operation
    Cause: Air cleaner clogged
    Fix: Check air filter element; Replace element
  • Noisy operation
    Cause: Exhaust system leaks
    Fix: Check silencer and connections for leaks; Replace gaskets and exhaust system components as necessary.
  • Generator set engine does not crank
    Cause: Battery connections
    Fix: Check for reversed or poor battery connections; Correct and tighten battery connections.
  • No output voltage
    Cause: DC output circuit breaker open
    Fix: Check for DC voltage on the generator side of circuit breaker; If there is DC 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
  • Loss of communication to accessory modules
    Cause: Bad connections
    Fix: Check wiring and connections; Verify that cable size and length of run comply with the instructions in the Installation Manual
  • High output voltage
    Cause: Incorrect controller settings
    Fix: Check genset model, engine model, system voltage, and other controller settings; Adjust the controller settings
  • Overheats
    Cause: Inadequate cooling
    Fix: Inspect engine and enclosure for air intake obstructions; Clear any air intake obstructions.
  • Volts L1-L2 DC High Shutdwn — Shutdown: The controller shut down the generator because the voltage measured from Phase A to Phase B exceeded the high limit for a time greater than the delay setting 2 seconds. Volts L1-L2 DC High Shutdwn
    Fix: Troubleshoot alternator. See Section 4.9, Troubleshooting Charts, and Section 5, Component Testing and Adjustment.
  • Variable Speed Start Command — Notice: A diagnostic exercise request has been received by the controller. VSpdStartCmd
    Fix: Check for a remote exercise command from OnCue.
  • System Ready — Notice: The digital output for System Ready (PIM) is active (contacts closed), indicating the generator has no active faults or warnings. System Ready

Compiled from service & troubleshooting documentation across every generator set that uses the Kohler CH-74.

Procedures

10
RDC2 Voltage Calibration Using SiteTech adjustment

Tools: digital voltmeter, personal computer, SiteTech software

  1. Connect PC to controller via USB
  2. With generator off, connect multimeter across L1/L2 (AC volts)
  3. Start generator set
  4. Compare voltmeter reading to controller display
  5. Calculate new Genset Calibration Factor Voltage using (Vmeter / Vcontrol) x Fold = Fnew
  6. Enter new value into SiteTech and click Apply Changes
  7. Verify voltmeter matches controller display
  8. Repeat for L2-L3 and L3-L1 if three-phase
  9. Press OFF to stop generator set
RDC2 Voltage Calibration Using the Controller Keypad adjustment

Tools: digital voltmeter

  1. With generator off, connect digital multimeter across L1 and L2, set to AC volts
  2. Start generator set with RUN button
  3. Navigate to Generator Metering menu, press Select; Volts L1-L2 displayed
  4. Press Select; voltage number flashes
  5. Use up/down arrows to match voltmeter reading
  6. Press Select to confirm
  7. Step to Return screen
  8. Press OFF to stop generator set
VSC Current (Load) Calibration Using the Controller Keypad adjustment

Tools: clamp-on DC current probe or DC current meter

  1. Connect DC current probe/clamp meter to measure generator current
  2. Start generator with RUN button
  3. Adjust system voltage to obtain rated current output with battery bank attached (or use load bank)
  4. Trip output breaker
  5. Navigate to Generator Metering menu, select Generator Load
  6. Press and hold Select for No-Load Calibration; verify breaker open, confirm Yes
  7. Close output breaker; verify rated output current, confirm Yes
  8. Verify displayed load is correct; recalibrate if necessary
  9. Press OFF to stop generator set
Firmware Update Using SiteTech maintenance

⚠ Do not load RDC2.4 firmware onto a red- or green-board controller

Tools: personal computer, USB cable, SiteTech software

  1. Download latest firmware file (.bin) from Kohler Power Resource Center or dealer portal
  2. Connect controller to PC via USB cable
  3. Start SiteTech; program recognizes connected device
  4. Click Update Firmware
  5. Browse to and select firmware file, click Open
  6. Verify current/new version and file name, click Update Firmware
  7. Wait for 'Firmware Updated Successfully' message, click Close
Setting the OnCue Password, RDC2 and VSC operation
  1. Press Select then down arrow to Networking Information menu
  2. Press Select for Networking Status
  3. Press Down arrow for Networking Configuration
  4. Press Select for Reset OnCue Password
  5. Press and hold Select until 'Reset OnCue Password? No' appears
  6. Press Up arrow to change No to Yes
  7. Press Select to reset; serial number and new password display for 10 seconds
Controller Replacement Procedure, Models 14RESA and 20RESA/B/C/D repair

⚠ Do not load settings from a green-board controller onto a red/blue-board controller or vice versa

Tools: voltmeter

  1. Review service kit information and confirm correct kits
  2. Open enclosure roof
  3. Press OFF button, disconnect utility power, verify with voltmeter
  4. Disconnect starting battery, negative lead first
  5. Remove two mounting screws, lift controller, disconnect harnesses
  6. Remove old controller
  7. If replacing original green-board controller with revised controller, install relay/breaker kit GM95104
  8. Reconnect harnesses, install new controller, reconnect battery negative last
  9. Reconnect utility power
  10. Set date/time/exerciser, update firmware, run Controller Setup and Voltage Calibration
  11. Replace covers/panels; reset OnCue password if used
Controller Replacement Procedure, Models 8/10/12RESV/L repair

⚠ Hazardous voltage can cause severe injury or death; disconnect all power sources before opening enclosure

⚠ Accidental starting can cause severe injury or death; disconnect battery cables, negative first

Tools: voltmeter, enclosure locking tool, screwdriver

  1. Open enclosure roof using locking tool
  2. Press OFF button on controller
  3. Disconnect utility power at building distribution panel; verify off with voltmeter
  4. Disconnect engine starting battery, negative lead first
  5. Remove two controller mounting screws and lift bottom edge of controller
  6. Note connections on back of controller, then disconnect all harnesses and leads
  7. Remove old controller
  8. Reconnect all harnesses to new controller assembly
  9. Install controller onto junction box with the two screws
  10. Reconnect battery, negative lead last
  11. Reconnect utility power by closing distribution panel breaker
  12. Set date/time and exerciser when prompted
  13. Check and update firmware to latest version via SiteTech or USB utility
  14. Perform Controller Setup (Section 5)
  15. Perform Voltage Calibration (Section 6)
Controller Replacement, Model RCL (RCL, RCLA, RCLB) repair

Tools: voltmeter

  1. Open/remove enclosure service door
  2. Press OFF, disconnect utility power
  3. Disconnect starting battery negative lead first
  4. Remove customer connection access panel, verify power off with voltmeter
  5. Remove two mounting screws, lift controller, disconnect P1/P2/P4/P5/P6
  6. Remove old controller, reconnect harnesses to new controller
  7. Install controller, replace access panel
  8. Reconnect battery and utility power
  9. Update firmware, set date/time/exerciser, run Controller Setup and Voltage Calibration
Controller Replacement, Models 14/20RCA/L repair

Tools: voltmeter

  1. Open enclosure roof, press OFF, disconnect utility power
  2. Disconnect starting battery negative lead first
  3. Remove two mounting screws, lift controller
  4. Verify utility power off at AC connections with voltmeter
  5. Disconnect harnesses, remove old controller
  6. Reconnect harnesses to new controller, install with screws
  7. Reconnect battery, reconnect utility power
  8. Set date/time/exerciser, update firmware, run Controller Setup and Voltage Calibration
VSC Controller Replacement, 6VSG repair

Tools: voltmeter

  1. Review service kit info, open enclosure roof
  2. Press OFF, disconnect utility power, verify with voltmeter
  3. Disconnect starting battery negative lead first
  4. Remove two mounting screws, lift controller, disconnect harnesses
  5. Remove old controller; if upgrading from green to revised board install relay kit GM92804
  6. Reconnect harnesses, install controller, reconnect battery negative last
  7. Reconnect utility power, update firmware
  8. Run Controller Setup and Voltage/Current Calibration
  9. Reset OnCue password if used

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

VoltagePhaseConnectionLeadsNotes
100/2001Single
100/2003Delta
110/2201Single
110/2203Delta
115/2301Single
1201SingleGenset System Voltage/Frequency/Phase table for controller setup
120/2083Wye
120/2401Single
120/2403Delta
127/2203Wye
2201Single
220/3803Wye
2301Single
230/4003Wye
2401Single
240/4163Wye
277/4803Wye

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

Which generators use the Kohler CH-74 engine?

The Kohler CH-74 powers 3 generator set(s), including Kohler 6VSG-24V, Kohler 6VSG-36V, Kohler 6VSG-48V.

What is a common problem with the Kohler CH-74 engine?

A commonly reported issue on generators using the Kohler CH-74 is: Stops suddenly. Cause: Fault shutdown. Fix: Check for a fault shutdown message on the controller display; Identify the cause of the fault; Correct the fault and then press the controller's OFF button to reset the controller.