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Home›Kohler›Kohler APM402

Kohler APM402 Generator Set

The Kohler APM402 is a generator set.

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Specifications

ControllerAPM402

Service specifications

20
TypeItemValueUnitCondition
GapSpeed sensor air gap0.36- 0.71mm
PressureBattery equalizer input voltage (24 volts nominal)20- 35volts
PressureBattery equalizer output voltage(input voltage/2) ±2%volts
PressurePressure switch 364345483 ±14kPa
ResistancePressure sender 264390 value A240 +17/- 15ohms at 0 psi
ResistancePressure sender 264390 value B153 +12/- 15ohms at 25 psi
ResistancePressure sender 264390 value C33.5ohms at 100 psi
ResistancePressure sender 365624 value A241 ±16ohms at 0 psi
ResistancePressure sender 365624 value B152 ±13ohms at 50 psi
ResistancePressure sender 365624 value C33.5ohms at 200 psi
ResistanceTemperature sender 226717 value A123.8 +7.2/- 7.8ohms at 90.6 C (195 F)
ResistanceTemperature sender 226717 value B35.6 +3.4/- 3.6ohms at 137.8 C (280 F)
ResistanceTemperature sender 226919 value A942 ±22ohms at 37.7 C (100 F)
ResistanceTemperature sender 226919 value B35ohms at 115.6 C (240 F)
SpeedOverspeed shutdown70Hz60 Hz models
TemperatureBattery equalizer operating temperature- 40 to 71C (- 40 F to 160 F)
TemperatureTemperature switch 241308107 ±4C (225 F ±7 F)normally open to close on temp. rise
TemperatureTemperature switch 290090/GM5170516 ±3C (60 F ±5 F)normally open to close on temp. fall
VoltageSpeed sensor voltage, wire 2 (black) & 16 (white)3- 6volts DC
VoltageSpeed sensor voltage, wire 2 (black) & 24 (red)8- 10volts DC

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

Procedures

12
Overfrequency Adjustment (Over/Underfrequency Relay, Decision-Maker 3+) adjustment
  1. Turn the overfrequency adjustment potentiometer fully clockwise (CW).
  2. Place master switch in RUN to start the generator set.
  3. Adjust governor per engine operation manual, engine service manual, or governor section of this manual.
  4. Slowly turn overfrequency potentiometer counterclockwise (CCW) until the LED starts flashing; after about 10 seconds the set shuts down on auxiliary fault.
  5. Place master switch to OFF/RESET to reset the controller.
  6. Place master switch to RUN to start the generator set.
  7. Readjust the governor to the desired frequency as required.
  8. Place master switch to OFF/RESET to stop the generator set.
Overvoltage Feature Testing and Adjustment (Decision-Maker 3+) adjustment

⚠ Hazardous voltage. Moving parts. Will cause severe injury or death. Operate the generator set only when all guards and electrical enclosures are in place.

⚠ Disconnecting the electrical load. Hazardous voltage will cause severe injury or death.

  1. Disconnect generator set from load by opening line circuit breaker or disconnecting and taping output leads.
  2. Determine overvoltage shutdown value based on user requirement; factory setting is 15% above nominal line-to-neutral voltage.
  3. Remove the controller cover.
  4. Place master switch in RUN to start the generator set.
  5. Observe AC voltmeter; turn voltage adjustment potentiometer CW until generator set shuts down.
  6. If the shutdown point is correct, go to step 12; otherwise continue.
  7. Turn controller circuit board R42 adjustment potentiometer fully CW.
  8. Place master switch to OFF/RESET to reset; then to RUN to start.
  9. Observe AC voltmeter while turning voltage adjustment potentiometer to desired overvoltage shutdown point.
  10. Turn R42 adjustment potentiometer slowly CCW until the generator set shuts down.
  11. Turn controller voltage adjustment potentiometer slightly CCW.
  12. Place master switch OFF/RESET then RUN to start; adjust for correct voltage and phase.
  13. Place master switch OFF/RESET to stop.
  14. Disconnect battery negative lead first; reconnect generator set to load; reconnect battery negative lead last.
Reactive Droop Compensator Adjustment Procedure adjustment

Tools: Voltmeter, Wattmeter

  1. Remove any load; start each generator set with master switch in RUN.
  2. Set reactive droop compensator rheostat on generator set no. 1 to minimum CCW; record rpm/frequency and voltage at 1/4 load steps to full load.
  3. Repeat for generator set no. 2.
  4. Compare readings; adjust voltage within 1 volt and speed within 3 rpm (or 0.1 Hz) at each load step.
  5. Check droop compensation on each unit with an inductive load 1/2 to full load.
  6. Adjust rheostat to approximately 4% below rated voltage at full load.
  7. Repeat for unit no. 2.
Reactive Droop Compensator Alternate Adjustment Procedure adjustment

Tools: Voltmeter

  1. Turn reactive droop compensator rheostat on generator set no. 1 to minimum setting.
  2. Remove controller cover; move voltage sensing lead from V7 to V9 at the AC fuse terminal block.
  3. Remove any load connected to the generator set.
  4. Start the generator set with master switch in RUN.
  5. Use controller or remote voltage adjusting potentiometer to fine adjust voltage.
  6. Apply resistive load (1.0 power factor) until reaching rated current.
  7. Adjust reactive droop compensator rheostat to achieve a 4% droop in voltage.
  8. Remove the resistive load and stop the generator set.
  9. Return voltage sensing lead from V9 to V7 at the AC fuse terminal block.
  10. Replace the controller cover and repeat for generator set no. 2.
Underfrequency Adjustment (Over/Underfrequency Relay, Decision-Maker 3+) adjustment
  1. Turn underfrequency adjustment potentiometer fully clockwise (CW).
  2. Place master switch in RUN to start the generator set.
  3. Adjust governor per engine operation manual, engine service manual, or governor section of this manual.
  4. Slowly turn underfrequency potentiometer counterclockwise (CCW) until LED starts flashing; after about 10 seconds the set shuts down on auxiliary fault.
  5. Place master switch to OFF/RESET to reset the controller.
  6. Place master switch to RUN to start the generator set.
  7. Readjust the governor to the desired frequency as required.
  8. Place master switch to OFF/RESET to stop the generator set.
2-Wire Low Water Level Sender Test diagnostic

⚠ Hot engine and exhaust system can cause severe injury or death. Do not work on the generator set until it cools.

⚠ Hazardous voltage. Moving parts. Will cause severe injury or death. Operate the generator set only when all guards and electrical enclosures are in place.

Tools: DC voltmeter

  1. Measure DC voltage between lead 31A (+) and ground (- ) with sender submerged in coolant; voltmeter indicates approximately 12.5 VDC.
  2. Measure DC voltage between lead 31A (+) and ground (- ) with sender removed from coolant for at least 5-15 seconds; voltmeter indicates a drop to approximately 7 VDC.
3-Wire Low Water Level Sender Test diagnostic

⚠ Hot engine and exhaust system can cause severe injury or death. Do not work on the generator set until it cools.

⚠ Hazardous voltage. Moving parts. Will cause severe injury or death.

Tools: Ohmmeter

  1. Measure resistance between lead 31 and ground with sender submerged in coolant; ohmmeter indicates a high resistance reading.
  2. Measure resistance between lead 31 and ground with sender removed from coolant for at least 5-15 seconds; ohmmeter indicates a low resistance reading.
Battery Equalizer Troubleshooting diagnostic

⚠ To prevent reverse polarity damage to the battery equalizer, remove the ground (GND) connection first and attach the ground connection last when disconnecting the battery equalizer.

Tools: 12-volt test light with alligator clips, Voltmeter with 0.01 volt resolution, Battery load tester

  1. Remove the ground (GND) connections from the battery equalizer; do not allow contact with other connections.
  2. Verify a differential of 12 volts between the +12 volt and +24 volt terminals using a 12-volt test light; the light will illuminate on a functional unit. Remove the test light.
  3. Connect the test light between the +12 volt and GND terminals; the light will illuminate on a functional unit.
  4. With the test light connected, measure and record the voltage between the +12 volt and +24 volt terminals.
  5. With the test light connected, measure and record the voltage between the +12 volt and GND terminals.
  6. Remove the test light.
  7. Compare the values from steps 4 and 5; the difference should be - 0.5 and +0.13 volts on a functional unit.
Oil Pressure Sender Testing diagnostic

Tools: Ohmmeter, Mechanical oil pressure gauge

  1. Disconnect the oil pressure sender lead 7C.
  2. Check the sender resistance with an ohmmeter.
  3. Compare resistance values when the generator set is shut down and when running at operating temperature to Section 1, Specifications.
  4. Use a mechanical oil pressure gauge to further verify correct readings.
Overcrank Test (Typical) diagnostic
  1. On gas-fueled sets, disconnect the coil wire at the distributor cap and ground it or disconnect the ignition system.
  2. On diesel-fueled sets, unplug the fuel injector harness from ECM or disconnect wire no. 70 from the injector pump solenoid.
  3. Place unit in RUN mode; observe 15-second on-off cranking cycles and maximum 75-second elapsed time to overcrank shutdown.
  4. Observe controller fault lamp and display for an overcrank shutdown.
  5. Place unit in OFF/RESET mode.
  6. Reconnect the ignition coil wire/ignition system, or reconnect the fuel injector harness/wire no. 70.
Speed Sensor Test with Generator Set Running diagnostic

⚠ Keep leads connected to the speed sensor terminals during the test; do not disconnect the leads.

Tools: DC voltmeter

  1. Connect a DC voltmeter between positive (+) lead (wire 24) at the speed sensor and ground (wire 2) with master switch OFF/RESET; read approximately 8- 12 volts DC.
  2. Place master switch in RUN to start the generator set.
  3. Connect DC voltmeter negative probe to 0 terminal (wire 16 white) and positive probe to positive (+) terminal (wire 24 red); read approximately 7- 12 volts DC.
  4. Place master switch in OFF/RESET to stop the generator set.
  5. If sensor emits a signal, check continuity of speed sensor leads (wires 2, 16, 24) between controller P1 connector and sensor terminals.
Speed Sensor Test with Separate 12 VDC Source diagnostic

Tools: DC voltmeter, 12-volt battery or DC power supply, Flat piece of iron or steel

  1. Place master switch in OFF/RESET position.
  2. Disconnect the speed sensor leads.
  3. Connect speed sensor, DC voltmeter, and DC voltage source as shown.
  4. Touch sensing surface with a flat piece of iron or steel at least 4.1 cm (1/4 cu. in.) in size.
  5. DC voltmeter reading should equal the source voltage, approximately 12 VDC.
  6. Remove the iron or steel piece and observe a voltmeter reading of 0 VDC.
  7. If the sensor passes, it is functional; replace if it fails.
  8. Connect the speed sensor leads and adjust the air gap.

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
APM402 and Decision-Maker 3000 P21P21-1 GND Shield; P21-2 (+) White; P21-3 (-) BlackConnect shield at either end but not at both ends.
APM603 customer connection terminal block(+) White; (-) Black; Shield — do not connect at the customer connection terminal block; tape to insulate unused endConnect shield at the RSA III P27 connection but not at the APM603 customer connection terminal block.
APM802 TB10TB10-7 (-) Blue; TB10-8 (+) Green; Shield — do not connect at TB10 or base module; tape to insulate unused end120 ohm resistor located on the base module; connect shield at the RSA III P27 connection only.
Communication module board TB5 (DEC 3+)TB5-3 ATS Position Input Return; TB5-4 User 1 Input Return; TB5-5 User 2 Input Return; TB5-6 User 3 Input Return; TB5-9 ATS Position Input; TB5-10 User 1 Input; TB5-11 User 2 Input; TB5-12 User 3 InputTerminals 1, 2, 7, and 8 not used. User 3 Input reserved for high battery volts (HBV) on DEC 3+ controllers.
Decision-Maker 3+ P21P21-1 - Black; P21-2 + White; P21-3 GND ShieldConnect shield at either end but not at both ends.
Decision-Maker 3500 TB12COM (+) (+) White; COM (-) (-) Black; Shield — do not connect at TB12 or DEC 3500, tape to insulate unused endConnect shield at the RSA III P27 connection only.
Decision-Maker 550 and 6000 P20P20-1 GND Shield; P20-2 + White; P20-3 - BlackConnect shield at either end but not at both ends.
Decision-Maker 8000 RS-485A terminal: blue wire, High (H) or Positive (+); B terminal: green wire, Low (L) or Negative (-)120 ohm resistor located on the controller base box; connect shield at the RSA III P27 connection only.
P27 connector on RSA III slaveP27-1 (-) Black (from master or previous slave); P27-2 (+) White (from master or previous slave); P27-3 Shield (from master or previous slave); P27-4 (-) Black (to next slave or terminating resistor); P27-5 (+) White (to next slave or terminating resistor); P27-6 Shield (to next slave or open)RS-485 daisy chain from master to slave.
P27 connector on master RSA IIIP27-1 (-) Black (from controller); P27-2 (+) White (from controller); P27-3 Shield (from controller); P27-4 (-) Black (to slave or terminating resistor); P27-5 (+) White (to slave or terminating resistor); P27-6 Shield (to slave or open)RS-485 communication from controller to RSA III master. Connect shield at either end but not both ends.
P27-1 (Controller to RSA III master)(-) Black (from controller)RS-485 communication; use Belden #9841 or equivalent.
P27-2 (Controller to RSA III master)(+) White (from controller)RS-485 communication.
P27-3 (Controller to RSA III master)Shield (from controller)Connect the shield wire at either end but not at both ends.
P27-4 (Master to slave)(-) Black (to slave or terminating resistor)RS-485 communication.
P27-5 (Master to slave)(+) White (to slave or terminating resistor)RS-485 communication.
P27-6 (Master to slave)Shield (to slave or open)RS-485 communication.
P37 power connectionsP37-1 Ground; P37-2 12/24 VDC battery input1 (not polarity sensitive); P37-3 12/24 VDC battery input2 (not polarity sensitive)Requires 12/24-volt, 200 mA (min.) DC power source; voltage should match generator set starting system.
P37-1GroundPower/CAN connections.
P37-212/24 VDC battery input1 (not polarity sensitive)Attach battery positive (+) at the starter solenoid.
P37-312/24 VDC battery input2 (not polarity sensitive)Attach battery negative (-) at the engine ground.
P40 output connectionsP40-1 Common fault relay normally closed; P40-2 Common fault relay common; P40-3 Common fault relay normally open; P40-4 Horn relay normally closed; P40-5 Horn relay common; P40-6 Horn relay normally openDry contacts rated at 220 VAC @ 0.8 amps and 30 VDC @ 2 amps.
P41 input connectionsP41-1 Local ATS emergency on input (EPS); P41-2 Local ATS emergency on input return (EPS); P41-3 User-Defined Digital input 1; P41-4 User-Defined Digital input 1 return; P41-5 User-Defined Digital Input 2; P41-6 User-Defined Digital Input 2 return; P41-7 User-Defined Digital Input 3; P41-8 User-Defined Digital Input 3 returnEPS and user-defined digital inputs typically supplied via remote Modbus RS-485 but may be hardwired locally.
P42 connectionsP42-1 User-defined digital input 4; P42-2 User-defined digital input 4 return; P42-3 User-defined digital input 5; P42-4 User-defined digital input 5 returnLocal user-defined digital inputs 4 and 5.

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

Troubleshooting

7

Fault codes

CodeMeaningRemedy
32High Coolant Temperature
32AEmergency StopReset the emergency stop switch.
40Pre High Coolant Temp.
41Pre Low Oil PressureCheck and adjust oil level or replace oil pump.
62Low Battery Volts
63Low FuelRefuel the generator set.
48Emergency Stop

Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.

Repair guides

13

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

Parts

1
Part #DescriptionQtySystem
APM402APM402 Controller1Controller Amazon eBay $875.00

Service, wear & replacement parts referenced for this model and its engine — confirm the exact part for your serial number. See the full parts catalog to search and cross-reference.

Available documents

Reference — NorthIowaCommunityCollege CaseStudy (Kohler)Parts manual — Kohler-Controller Brochure (Kohler)Service manual — Annunciators tt1625 (Kohler)Service manual — Kohler APM402 Controller (Discovery Energy)Service manual — TP-6356 (Kohler)Service manual — tt1625 (Kohler)

This page was generated from the 6 manufacturer documents above by automated extraction; every figure shown is copied from one of them. How the data is compiled.