The Cummins/Onan 6BT5.9 is a 5.9 L 6-cylinder engine. It powers generator sets from AKSA and Cummins/Onan, including the AC110, 100 DGDB, 65DGDA and 80 DGDA. It holds 16 L (4.2 gal) of oil and 25 L (6.6 gal) of coolant.
Also known as: Cummins 6BT5.9
Part of the Cummins/Onan 6BT5.9 engine family — 6 variants share parts & fitment.
| Oil capacity | 16.0 L |
|---|---|
| Coolant capacity | 25.0 L |
| Displacement | 5.9 L |
| Cylinders | 6 |
Shared across brands: AKSA, Cummins/Onan
| Code | Meaning | Remedy |
|---|---|---|
| RUN | Run | |
| FAULT 1 | Fault 1 | |
| FAULT 2 | Fault 2 | |
| K13 | K13 - HET | |
| K4 - Fault 2 | K4 - Fault 2 | |
| K5 - Fault 1 | K5 - Fault 1 | |
| K17 | K17 - PHET | |
| K19 | K19 - PLOP | |
| ES-1859-1 | Overvoltage Monitor | Shut down the output device and trip an optional circuit breaker |
| ES-1852 | Overload Detector | Shut down the output device |
| Symptom | Cause | Remedy |
|---|---|---|
| Voltage regulator may require adjustment or is faulty | Voltage, the voltage regulator may require adjustment or is faulty | Refer to Tests and Adjustments section for adjustments, replace if faulty. |
| Shutdown was due to over/under frequency | If shutdown was due to over/under frequency, the engine governor may require adjustment or is faulty | Refer to Tests and Adjustments section for adjustments, replace if faulty. |
| No fault lamp lit | Possible defective ECM Check fuses F4 and F2 of ECM board A11. | Perform restart and check for B+ voltage in at TB1-9 and voltage out at TB1-10 to fuel solenoid. If there is voitage out at TB1-10, check fuel supply solenoid, shutoff valves, etc. If there is no voltage out at TB1-10, ECM board A11 is defective. Replace. |
| AC output voltage too high or low | Is engine running at correct rpm? No; Are generator output connections correct and secure? Yes; Does adjustment of Voltage Adjust control R21 (if equipped) result in correct output voltage? No; Check Voltage Regulator Adjustment. Check ok? No; Check condition of rotating diodes. | Visually inspect for loose connections, faulty diodes, etc. Check ok? Yes; Do not replace Voitage Regulator Replace Voltage Regulator VR21. ACAUTION VR21 until external trouble has been corrected to avoid possible damage to new regulator board. |
| Exciter field breaker trips (if equipped) | Does AC output voltage build up to 150% or more of rated voltage before breaker trips? No; Check diodes in rotor assembly. Replace if bad. | Check Voltage Regulator adjustments and connections. Check generator stator leads for proper, secure connection. Refer to appropriate electrical schematic. Check exciter rotor winding. Replace if bad. Check generator rotor field winding. Replace if bad. Check generator stator windings. Replace if bad. Do not replace Voltage Regulator Replace Voltage Regulator VR21. ACAUTION VR27 until external trouble has been corrected to avoid possible damage to new regulator board. |
Fault codes and symptom→remedy steps extracted from this engine’s service/owner documentation; verify against the official manual before servicing.
| Part # | Description | Category |
|---|---|---|
| 982-0200 | Air Filter | air_filter |
| 3824469 | fuel pump gear puller | fuel_pump |
| DM-3801372 | Gasket Set - 6BT 5.9 | gasket |
| FP-6B59PREM | 6B/6BT5.9 In-Frame Kit w/upper gasket set & oil pan gasket | gasket |
| FP-6B59PREML | 6B/6BT5.9 In-Frame Kit w/upper gasket set & oil pan gasket (late) | gasket |
| FP-IFK6B59PREM | 6B/6BT5.9 In-Frame Kit w/upper gasket set & oil pan gasket | gasket |
| FP-IFK6B59PREML | 6B/6BT5.9 In-Frame Kit w/upper gasket set & oil pan gasket (late) | gasket |
| 3822509 | injector puller | injector |
| 3823276 | injector bore brush | injector |
| DM-3029551 | Fuel Injector - 6BT 5.9 | injector |
| LF3349 | Lube, Full-Flow Spin-On | lube_filter |
| 3377259 | bosch timing tool (ve) | other_service |
| 960-0627C | other_service | |
| 965-0520 | Cooling Fan | other_service |
| DM-3802010 | Main Bearing Set Standard - 4BT 3.9, 6BT 5.9, 6CT 8.3 | other_service |
| FP-3356970 | 6B/6BT5.9 In-Frame Kit (contains FP-3802160 Piston Kit) | other_service |
| FP-3356971 | 6B/6BT5.9 In-Frame Kit (contains FP-3802248 Piston Kit) | other_service |
| GM12641 | Safety/locking agent | other_service |
| GM12657 | Dipstick | other_service |
| GM12676 | Cylinder liner | other_service |
| GM12678 | Screw plug | other_service |
| GM12697 | Torx-head bolt | other_service |
| GM12921 | Hexagon bolt | other_service |
| GM12924 | Rear end cover | other_service |
| GM12936 | Wrapped bearing bush | other_service |
| GM12937 | Wrapped bearing bush | other_service |
| GM12954 | Dipstick | other_service |
| GM12970 | Compression spring | other_service |
| GM13175 | Pipe clamp | other_service |
| S103 | selector switch on the control PCB | other_service |
| TB1-6 | terminals between TB1-5 and TB1-7 in the control box | other_service |
| TB1-7 | terminals between TB1-6 and TB1-8 in the control box | other_service |
| DM-3805401 | Oil Pump - 6BT 5.9 | pump |
| DM-3805403 | Water Pump - 4BT 3.9, 6BT 5.9 | pump |
| GM12667 | Sealing ring | seal |
| DM-3015282 | Thermostat 180F - 4BT 3.9, 6BT 5.9 | thermostat |
Parts cataloged across all variants of this engine family — verify the exact part fits your specific variant and serial number before ordering.
Parts listed by aftermarket suppliers as fitting this engine — leads compiled from supplier catalogs; verify the exact part for your serial number.
The Cummins/Onan 6BT5.9 engine has an oil capacity of 16.0 liters.
The Cummins/Onan 6BT5.9 has a displacement of 5.9 liters with 6 cylinders.
The Cummins/Onan 6BT5.9 powers 7 generator set(s), including AKSA AC110, Cummins/Onan 100 DGDB, Cummins/Onan 65DGDA, Cummins/Onan 80 DGDA, Cummins/Onan 85DGDB.