Mitsubishi 3.9L Engine Engine
The Mitsubishi 3.9L is a 3.9 L engine. It powers generator sets from Generac, including the QT 40kW.
Also known as: Mitsubishi 3.9L, 3.9L
Generator sets powered by this engine
1Troubleshooting
9Fault codes
| Code | Meaning |
|---|
| L3 | Circulation water temperature overheat protection |
| L4 | DHW tank water temperature overheat protection |
| L5 | Indoor unit temperature thermistor (THW1, THW2, THW5A, THW5B, THW6, THW7, THW8, THW9) failure |
| L6 | Circulation water freeze protection |
| L8 | Heating operation error |
| L9 | Low primary circuit flow rate detected by flow sensor or flow switch (flow switches 1, 2, 3) |
| LA | Pressure sensor failure |
| LB | High pressure protection |
| LC | Boiler circulation water temperature overheat protection |
Fault codes and symptom→remedy steps extracted from this engine’s service/owner documentation; verify against the official manual before servicing.
Common problems
7- No AC output from generator.
Cause: Defective Control Module circuit board
Fix: *Contact the nearest Authorized Dealer for assistance. - Engine won’t crank.
Cause: 1. 15 amp fuse blown. 2. Loose or corroded or defective battery cables. 3. Defective starter contactor. 4. Defective starter motor. 5. Dead or Defective Battery. 6. 5 amp fuse blown.
Fix: 1. Replace fuse. 2. Tighten, clean or replace battery cables as necessary. 3. Replace contactor.* 4. Replace starter motor.* 5. Remove, change or replace battery. 6. Replace fuse.* - Engine starts then shuts down.
Cause: AUTO/OFF/MANUAL Switch at OFF, engine continues to run
Fix: *Contact the nearest Authorized Dealer for assistance. - Engine starts hard, runs rough.
Cause: 1. Flame arrestor (air cleaner) plugged or damaged. 2. Plugged fuel line. 3. Defective spark plugs. 4. Fuel pressure incorrect.
Fix: 1. Clean or replace as needed. 2. Unclog fuel line. 3. Clean, regap or replace plugs. 4. Confirm fuel pressure to regulator is as recommended in SPECIFICATIONS. - Engine cranks but won't start
Cause: 1. Out of fuel. 2. Fuel solenoid (FS) is defective 3. Open Wire #14A from Engine Control circuit board. 4. Spark plugs defective. 5. Door on tank not closed.
Fix: 1. Replenish fuel. 2. Replace solenoid.* 3. Reconnect wire. 4. Clean, regap or replace plugs. 5. Close door on tank. - Defective AUTO/OFF/MANUAL switch.
Cause: 1. Open/disconnected wire #15A between AUTO/OFF/MANUAL switch and Control Module circuit board.
Fix: Replace switch.* Reconnect/close wire. - DANGER Safety 001
Compiled from service & troubleshooting documentation across every generator set that uses the Mitsubishi 3.9L.
Common questions
What is the displacement of the Mitsubishi 3.9L?
The Mitsubishi 3.9L has a displacement of 3.9 liters.
Which generators use the Mitsubishi 3.9L engine?
The Mitsubishi 3.9L powers 1 generator set(s), including Generac QT 40kW.
What is a common problem with the Mitsubishi 3.9L engine?
A commonly reported issue on generators using the Mitsubishi 3.9L is: No AC output from generator.. Cause: Defective Control Module circuit board. Fix: *Contact the nearest Authorized Dealer for assistance..