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Cummins/Onan D6T Engine

The Cummins/Onan D6T is a 2.5 L naturally aspirated engine. It powers generator sets from Cummins/Onan, including the C12 D6.

Also known as: Cummins D6T

2.5 L

Displacement

On this pageSpecs Generator sets FAQ Torque & specs Fluids Fault codes

Engine specifications

Displacement	2.5 L
Aspiration	naturally aspirated

Generator sets powered by this engine

Cummins/Onan C12 D6

How to read your Cummins/Onan engine serial & model number →

Common problems

Undervoltage sensor pickup and dropout adjustable from 85-100% and 75-98%
Fix: Dropout adjustable delay from 0.1-30 sec.
Under frequency shutdown 81 u
Time delay start and stop (cooldown) configurable for time delay of 0-300 seconds prior to starting after receiving a remote start signal
Fix: Control provides retransfer time delays including time delay emergency to normal (0-1800 sec), programmed transition delay (0-600 sec), and time delay engine cooldown (0-3600 sec).
Time delay of 0-600 seconds prior to shutdown after signal to stop in normal operation modes
Fix: Default for both time delay periods is 0 seconds.
Sensor failure indication
Fix: Logic is provided on the base control to detect analog sensor or interconnecting wiring failures.
Overvoltage sensor dropout adjustable from 105-135% of nominal
Fix: Dropout adjustable delay from 0.5-120 sec.
Over/under frequency sensor underfrequency sensing pickup and dropout adjustable from 85-100% and 70-85%
Fix: Dropout adjustable delay from 0.1-15 sec.
Over/under frequency sensor overfrequency sensing dropout adjustable from 105-115% of nominal
Fix: Dropout adjustable delay from 0.1-15 sec.
Over frequency shutdown/warning 81 o
Low lube oil pressure warning/shutdown
Fix: Level is pre-set to match the capabilities of the engine used. Control includes time delays to prevent nuisance shutdown signals.
Low coolant temperature warning
Fix: Indicates that engine temperature may not be high enough for 1 min. and start or proper load acceptance.
Low AC voltage shutdown 27
High Current warning/shutdown 51
High coolant temperature warning/shutdown
Fix: Level is pre-set to match the capabilities of the engine used. Control includes time delays to prevent nuisance shutdown signals.
High AC voltage shutdown 59

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan D6T.

Service specifications

Type	Item	Value	Unit	Condition
Other	AC waveform Total Harmonic Distortion (THDV)	No load to full linear load < 5. For any single harmonic < 2.5	%
Other	Governor regulation class	ISO 8528
Other	Telephone Harmonic Factor (THF)	< 2	%	for 50 Hz
Other	Telephone Influence Factor (TIF)	< 75		for 60 Hz
Speed	Frequency regulation	Droop
Speed	Random frequency variation	± 0.75	%
Temperature	Standard temperature rise	125-163	ºC
Voltage	Random voltage variation	± 2.5	%
Voltage	Starting voltage	12	V	negative ground
Voltage	Voltage regulation, no load to full load	± 2.5	%	no load to full load

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

Recommended fluids

Fluid	Grade	Standard	Ambient	Capacity	Notes
Coolant	Antifreeze 50/50 (Ethylene glycol)				Optional
Fuel	Diesel

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

Fault codes

Code	Name	Meaning	Severity
27	Low AC voltage shutdown	Voltage on any phase has dropped below a preset value. Adjustable over a range of 50-95% of voltage, time delay 2-20 seconds. Default value is 90% for 5 seconds.	Shutdown
51	High Current warning/shutdown	Implementation of the thermal damage curve with instantaneous trip level calculated based on current transformer ratio and application power rating.	Warning
59	High AC voltage shutdown	Output voltage on any phase exceeds pre-set values. Values adjustable from 105-125% of nominal voltage, with time delay adjustable from 1-10 seconds. Default value is 110% for 5 seconds.	Shutdown
81 o	Over frequency shutdown/warning	Generator set is operating at a potentially damaging frequency level. Settings are adjustable from 2-10 Hz above nominal governor set point for 100-2000 half cycles delay. Default: 5 Hz, 1000 half cycles.	Warning
81 u	Under frequency shutdown	Generator set output frequency cannot be maintained. Settings are adjustable from 2-10 Hz below nominal governor set point, for a 500-2000 half cycles delay. Default: 5 Hz, 1000 half cycles.	Shutdown

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

Common questions

What is the displacement of the Cummins/Onan D6T?

The Cummins/Onan D6T has a displacement of 2.5 liters.

Which generators use the Cummins/Onan D6T engine?

The Cummins/Onan D6T powers 1 generator set(s), including Cummins/Onan C12 D6.

What is a common problem with the Cummins/Onan D6T engine?

A commonly reported issue on generators using the Cummins/Onan D6T is: Undervoltage sensor pickup and dropout adjustable from 85-100% and 75-98%. Fix: Dropout adjustable delay from 0.1-30 sec..