Kohler CH25 Engine

Shared across brands: Cummins/Onan, Genmac

How to read your Kohler engine serial & model number →

• Engine overspeed — Test 2: Manually hold the engine at the desired running speed, measure the DC voltage between terminals E(+) and H(-) on the speed control unit
  Cause: If the voltage reading is 1.0 to 1.5 VDC: speed adjustment set above desired speed; defective speed control unit
  Fix: Turn counterclockwise
• Engine remains below desired speed — Test 1: measure the actuator output, terminals G & H, while running
  Cause: If voltage measurement is within 1.5 volts or more
• Engine overspeed — Test 1: Do not crank, apply DC power to the governor system
  Cause: Actuator goes to full fuel
  Fix: Then disconnect speed sensor terminals C and D; if actuator still at full fuel — speed control unit defective; if actuator at minimum fuel position — erroneous speed signal, check speed sensor cable
• Engine governing system does not function (system inoperative) — Step 4: terminals E(+) & H(-), normal reading 0.8-1.5 V while cranking
  Cause: Wiring error to actuator; defective speed control unit; defective actuator
• Engine governing system does not function (system inoperative) — Step 3: terminals C(+) & D(-), normal reading 1.0 VAC RMS min. while cranking
  Cause: Gap between speed sensor and gear teeth too great; improper or defective wiring to the speed sensor; defective speed sensor
  Fix: Check gap; resistance between D & C should be 30 to 1200 Ω
• Engine governing system does not function (system inoperative) — Step 2: terminals A(+) & B(-), normal reading 0-3.9 with speed trim, 7.1-7.9 without speed trim
  Cause: Speed trim shorted or miswired; defective unit
• Engine governing system does not function (system inoperative) — Step 1: terminals E(+) & F(-), normal reading battery supply voltage (12 VDC)
  Cause: DC battery power not connected; blown fuse; low battery voltage; wiring error
• Actuator does not energize fully while cranking — Test 2: momentarily connect terminal E to H; the actuator should move to the full fuel position
  Cause: Actuator or battery wiring in error; actuator or linkage binding; defective actuator
  Fix: Replace actuator
• Actuator does not energize fully while cranking — Test 1: measure the DC voltage between terminals E(+) and H(-) on the speed control unit; should be 0.8 to 1.5 volts, if not
  Cause: Weak or undersized battery; actuator wiring incorrect; if voltage is greater than 1.5V, speed set too low
  Fix: Replace the battery if weak or undersized

Compiled from service & troubleshooting documentation across every generator set that uses the Kohler CH25.

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

• Adjust Governed Idle Speed
• Adjust Low Idle Fuel
• Adjust Low Idle Speed (RPM)
• Test Crankcase Vacuum

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

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

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

Parts listed by aftermarket suppliers as fitting this engine — leads compiled from supplier catalogs; verify the exact part for your serial number.