Onan QG 4000 generator fault codes
Reviewed 3 primary sourcesSee sources
The QG 4000 is Onan’s KY series. Two operator manuals cover different spec letters and differ in places, such as overcrank time, so both are shown. The spec letter is on the generator’s nameplate.
Cummins Onan · RV generator · QG 4000 (KY). Models: KY Spec J–N, KY Spec P–R.
Cummins’s QG 4000 spec sheet lists the KY models and names operator manual 981-0159.[3]
How to read the code
After a shutdown the status light blinks: 3 blinks means a service fault. Press STOP (STOP/PRIME on later units) once and it blinks the two-digit code, tens first, then units. 4 blinks means the engine cranked too long without starting.[1]
Codes: Spec J–N (manual 981-0159)
| Code | Meaning | What to do | Who fixes it |
|---|---|---|---|
| 3 | Service check: first-level code; read the second-level code. | Press STOP once to show the two-digit code.[1] | Check, then service if it persists |
| 4 | Overcrank: cranking exceeded about 15-20 s without starting (the manual gives both 15–20 s and 20 s). | Gasoline: fill tank (generator pickup sits higher than vehicle engine's), prime at Stop/Prime 30 s. LPG: fill container (keep at least half full on cold days). Open fuel valves; secure/replace spark plug; service air cleaner.[1] | Check, then service if it persists |
| 12 | Overvoltage: controller cannot maintain rated voltage. | Not an owner fix. See an authorized Onan dealer.[1] | Technician |
| 13 | Undervoltage: controller cannot maintain rated voltage. | Reduce connected appliances, especially air conditioners and battery chargers.[1] | Owner check |
| 14 | Overfrequency: governor cannot hold rated frequency. | Not an owner fix. See an authorized Onan dealer.[1] | Technician |
| 15 | Underfrequency: governor cannot hold rated frequency. | Reduce connected appliances, especially air conditioners and battery chargers.[1] | Owner check |
| 27 | Voltage sense: controller cannot sense output voltage. | Not an owner fix. See an authorized Onan dealer.[1] | Technician |
| 29 | High battery voltage: over 19 V across battery system. | Make sure 12 V batteries serving generator are in parallel, not series; select lower boost charge rate.[1] | Owner check |
| 32 | Low cranking speed: under 180 rpm for over 2 s. | Clean and tighten the battery connections, recharge or replace the battery, and use oil of the right viscosity.[1] | Owner check |
| 35 | Control card failure: microprocessor EEPROM self-test error. | Not an owner fix. See an authorized Onan dealer.[1] | Technician |
| 36 | Engine stopped without command from controller. | Gasoline: fill tank (generator pickup sits higher than vehicle engine's), prime at Stop/Prime 30 s. LPG: fill container (keep at least half full on cold days). secure/replace spark plug; service air cleaner. Check for mechanical damage.[1] | Check, then service if it persists |
| 37 | Invalid generator configuration (factory preprogrammed). | Not an owner fix. See an authorized Onan dealer.[1] | Technician |
| 38 | Overcurrent: low power factor loads. | Reduce simultaneous appliances (especially air conditioners); have appliances checked (locked compressor rotor).[1] | Check, then service if it persists |
| 41 | Generator rotor: cannot sense field or output voltage. | Not an owner fix. See an authorized Onan dealer.[1] | Technician |
| 42 | Processor: microprocessor ROM self-test error. | Not an owner fix. See an authorized Onan dealer.[1] | Technician |
| 43 | Processor: microprocessor RAM self-test error. | Not an owner fix. See an authorized Onan dealer.[1] | Technician |
| 45 | Speed sense: cannot sense quadrature frequency. | Not an owner fix. See an authorized Onan dealer.[1] | Technician |
| 47 | Ignition: controller cannot sense ignition. | Not an owner fix. See an authorized Onan dealer.[1] | Technician |
| 48 | Generator field sense: cannot sense field voltage. | Not an owner fix. See an authorized Onan dealer.[1] | Technician |
Codes: Spec P–R (manual A041D131)
| Code | Meaning | What to do | Who fixes it |
|---|---|---|---|
| 3 | Service check: see second-level code. | Press STOP/PRIME once to see the two-digit code.[2] | Check, then service if it persists |
| 4 | Over crank: cranking exceeded 30 s without starting. | Fill fuel tank if low and prime at STOP/PRIME 30 s; LPG: fill container (half full on cold days); secure/replace spark plugs; replace dirty air filter. Replace oil with correct viscosity; tighten leaking fuel fittings and reprime; replace fuel filter.[2] | Check, then service if it persists |
| 12 | Over voltage: control cannot maintain rated voltage. | Not an owner fix. Contact a Cummins Onan dealer or distributor.[2] | Technician |
| 13 | Under voltage. | Reduce connected appliances (air conditioners, battery chargers).[2] | Owner check |
| 14 | Over frequency: governor cannot maintain rated frequency. | Not an owner fix. Contact a Cummins Onan dealer or distributor.[2] | Technician |
| 15 | Under frequency. | Reduce connected appliances (air conditioners, battery chargers).[2] | Owner check |
| 27 | Voltage sense: cannot sense output voltage. | Not an owner fix. Contact a Cummins Onan dealer or distributor.[2] | Technician |
| 29 | High battery voltage: over 19 V. | Connect 12 V batteries in parallel, not series; select lower boost charge rate.[2] | Owner check |
| 32 | Low cranking speed: under 180 RPM for over 2 s. | Clean and tighten the battery connections, recharge or replace the battery, and make sure the oil is the right viscosity.[2] | Owner check |
| 35 | Control card failure: EEPROM self-test error. | Not an owner fix. Contact a Cummins Onan dealer or distributor.[2] | Technician |
| 36 | Engine stopped without command from control. | Fill fuel tank if low and prime at STOP/PRIME 30 s; LPG: fill container (half full on cold days); secure/replace spark plugs; replace dirty air filter. Check for mechanical damage.[2] | Check, then service if it persists |
| 37 | Invalid generator set configuration: frequency/RPM ratio wrong. | Not an owner fix. Contact a Cummins Onan dealer or distributor.[2] | Technician |
| 38 | Over current (field overload): low power factor loads. | Reduce load; have air conditioners/appliances checked.[2] | Check, then service if it persists |
| 41 | Generator rotor: cannot sense field or output voltage. | Not an owner fix. Contact a Cummins Onan dealer or distributor.[2] | Technician |
| 42 | Processor: ROM self-test error. | Not an owner fix. Contact a Cummins Onan dealer or distributor.[2] | Technician |
| 43 | Processor: RAM self-test error. | Not an owner fix. Contact a Cummins Onan dealer or distributor.[2] | Technician |
| 45 | Speed sense: cannot sense quadrature frequency. | Not an owner fix. Contact a Cummins Onan dealer or distributor.[2] | Technician |
| 47 | Ignition: cannot sense ignition. | Not an owner fix. Contact a Cummins Onan dealer or distributor.[2] | Technician |
| 48 | Generator field sense: cannot sense field voltage. | Not an owner fix. Contact a Cummins Onan dealer or distributor.[2] | Technician |
When to call a technician
Codes marked as service items need an authorized Cummins Onan dealer; the manual reserves deeper fault-finding for trained technicians.[1] Our mobile RV repair listings cover Colorado Springs and the Boise area so far.
Sources
Facts on this page are restated from the manufacturer documents below. Codes differ by model and spec letter, so check the manual for your exact unit. We have not tested these codes on equipment.
- Operator Manual RV Generator Set KY (Spec J-N)Cummins Inc. (Onan) · 981-0159 · Safety pp. iii–iv; fault codes and troubleshooting section 4 · retrieved
- Operator Manual - Onan Generator Set for RV, KY (Spec P-R)Cummins Inc. (Onan) · A041D131 · Safety section 1; fault codes section 6 · retrieved
- RV QG 4000 specification sheetCummins Inc. (Onan) · A-1399n · Model list and operation manual reference · retrieved
Primary publishers: Cummins Inc. (Onan). Spotted an error? Email the address in the footer with the model and the document you are using.