6C Engine

The 6C is a turbocharged engine. It powers generator sets from Cummins/Onan, including the 3100 series.

Also known as: 6C

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

Engine specifications

Aspiration	Turbocharged

Generator sets powered by this engine

Cummins/Onan 3100 series

Common problems

WEAK BATTERY 232
Warning lamp lights. MESSAGE: LOW DC VOLTAGE 230
Fix: Indicates battery voltage is below 10 VDC. a. Discharged or defective battery. Check the battery charger fuse. Recharge or replace the battery. b. Poor battery cable connections. Clean the battery cable terminals and tighten all connections. c. Check engine DC alternator. Replace engine DC alternator if normal battery charging voltage is not obtained. d. Check battery charge voltage float level if applicable (raise float level).
Warning lamp lights. MESSAGE: LOW COOLANT TEMP 210
Fix: Set is not operating. Warning occurs when engine coolant temperature is 70° F (21° C) or lower. NOTE: In applications where the ambient temperature falls below 40°F (4°C), Low Coolant Temp may be indicated even though the coolant heaters are operating. Indicates engine coolant heater is not operating or is not circulating coolant. Check for the following conditions: a. Coolant heater not connected to power supply. Check for blown fuse or disconnected heater cord and correct as required. b. Check for low coolant level and replenish if required. Look for possible coolant leakage points and repair as required. c. Open heater element. Check current draw of heater.
Warning lamp lights. MESSAGE: HIGH DC VOLTAGE 231
Fix: Indicates battery voltage is above 14.5 VDC.
Warning lamp lights. MESSAGE: HIGH COOLANT TEMP 211
Fix: Indicates the engine coolant temperature is getting close to the recommended maximum temperature limit: 215° F (102° C) – standby or 207° F (97° C) – prime. If generator is powering non-critical and critical loads and cannot be shut down, use the following: a. Reduce load if possible by turning off non-critical loads. b. Check air inlets and outlets and remove any obstructions to airflow. If engine can be stopped, follow HIGH COOLANT TEMP 212 – SHUT-DOWN procedure. To check coolant temperature, access the coolant temperature menu prior to clearing the fault.
Warning lamp lights. MESSAGE: COOLANT SENDER 213
Fix: Indicates that the resistance of the coolant temperature sender is out of range. Check the resistance of the sender. Resistance should be 500 to 2k ohms.
UNDER FREQUENCY 313
Shutdown lamp lights. MESSAGE: MAG PICKUP 220
Fix: Indicates mag pickup speed indication is not being sensed or does not match generator set output frequency. a. Restart and check RPM on the digital display.
Shutdown lamp lights. MESSAGE: LOW COOLANT LVL or LOW COOLANT LVL 214, 215
Fix: Indicates engine coolant level has fallen below the trip point. Allow engine to cool down completely before proceeding. a. Check coolant level in both radiator and coolant recovery bottle and replenish if low. Look for possible coolant leakage points and repair if necessary. b. If radiator level is low and coolant bottle level is correct, defective coolant bottle hose or radiator cap. c. Reset control and restart after locating and correcting problem. LOW COOLANT LVL Shutdown will not occur if genset is in Idle mode (low coolant warning only).
Shutdown lamp lights. MESSAGE: HIGH COOLANT TEMP 212
Fix: Indicates engine has overheated (coolant temperature has risen above the shutdown trip point: 223° F (106° C) – standby or 215° F (102° C) – prime. Allow engine to cool down completely before proceeding with the following checks: a. Check for obstructions to cooling airflow and correct as necessary. b. Check fan belt and repair or tighten if necessary. c. Check coolant mixture. d. Check blower fan and circulation pumps on remote radiator installations. e. Reset control and restart after locating and correcting problem.
Shutdown lamp lights. Engine stops cranking. MESSAGE: FAIL TO CRANK 221
Fix: Indicates possible fault with control or starting system. Check for the following conditions: a. Check fuse F3 on the Engine Interface board. b. Poor battery cable connections. Clean the battery cable terminals and tighten all connections. c. Discharged or defective battery. Recharge or replace the battery.
SHORT CIRCUIT 322
RUPTURE BASIN* 262
REVERSE POWER 335
OVERSPEED 223

Compiled from service & troubleshooting documentation across every generator set that uses the 6C.

Maintenance schedule

Item	Spec	Capacity	Part #	Interval
Air filter			—
Fuel filter			—
Oil filter			—
Battery			—
Belt			—
Coolant			—
Oil			—
Spark plug			—

Pooled from every document that names this exact engine — confirm the interval and part number against your unit's serial number.

Service specifications

Type	Item	Value	Unit	Condition
Injection timing	Ignition timing GGKB/GGKC (preferred)	28 to 32	degrees BTDC
Injection timing	Ignition timing GGKD (preferred)	26 to 30	degrees BTDC
Other	Exhaust O2 (excess oxygen)	5 ±1	%	rated load and rpm
Other	Fuse A31-F1 (control B+)	5	Amp	Engine Interface board
Other	Fuse A31-F3 (auxiliary B+)	5	Amp	Engine Interface board; panel lights, run and start relays
Other	Fuse A38-F1 (Network B+)	10	Amp	Governor Output Module
Other	Fuse A38-F2 (Switched B+)	10	Amp	Governor Output Module
Other	Fuse A38-F3 (Governor B+)	10	Amp	Governor Output Module
Other	Fuse TB-Bat F1 (Customer B+)	20	Amp	Engine Harness Assembly
Other	Setup/calibration menu access code	574
Other	Start delay adjustment range	0 to 300	seconds	remote starting in Auto mode
Other	Stop delay adjustment range	0 to 600	seconds	remote stopping in Auto mode
Other	Voltage regulator PWM duty cycle range	0 - 60	%	normal duty cycle less than 10%
Pressure	Fuel supply pressure to gas regulator (maximum permissible at any load)	20	inches WC
Pressure	Fuel supply pressure to gas regulator (minimum at full load)	10	inches WC	full load
Pressure	Idle oil pressure (6C engine)	10-30	psi (69-207 kPa)	idle
Pressure	Idle oil pressure (normal)	10-30	psi (69-207 kPa)	Engine model 6C, idle
Pressure	Idle oil pressure shutdown limit	8	psi (55 kPa)	Engine model 6C, idle
Pressure	Idle oil pressure shutdown limit (6C engine)	8	psi (55 kPa)	idle
Pressure	Idle oil pressure warning limit	12	psi (83 kPa)	Engine model 6C, idle
Pressure	Idle oil pressure warning limit (6C engine)	12	psi (83 kPa)	idle
Pressure	Intake manifold pressure (maximum)	15	psi	rated load
Pressure	LP gas pressure (full load)	-1.0	inches WC	full load
Pressure	LP gas pressure (no load)	-0.5	inches WC	no load
Pressure	NG gas pressure on mixer side	4 to 6	inches WC	full load
Pressure	Normal oil pressure	40 - 70	psi (276 - 483 kPa)	Engine model 6C
Pressure	Normal oil pressure (6C engine)	40 - 70	psi (276 - 483 kPa)	normal
Pressure	Oil pressure shutdown limit	15	psi (103 kPa)	Engine model 6C
Pressure	Oil pressure shutdown limit (6C engine)	15	psi (103 kPa)	normal
Pressure	Oil pressure warning limit	20	psi (138 kPa)	Engine model 6C
Pressure	Oil pressure warning limit (6C engine)	20	psi (138 kPa)	normal
Resistance	A31 AVR drive continuity (A31 J1-2 to J4-10 and A31 J1-1 to J4-11)	270	ohms
Resistance	Coolant temperature sender resistance	500 to 2k	ohms
Resistance	Exciter stator/rotor winding insulation resistance	greater than 1	megohm	Replace if less than 1 megohm
Resistance	PMG winding resistance	approximately 4.4	ohms	across lead pairs P2-P3, P3-P4 and P4-P2
Resistance	PMG winding resistance (each winding)	approximately 4.4	ohms
Resistance	PT primary resistance	1K-2.5K	ohms
Resistance	PT secondary resistance	140-225	ohms
Resistance	PT/CT module 3-ohm resistors (J8-15 to 14, J8-22 to 23, J8-7 to 8)	3	ohms
Speed	Backup start disconnect initiation	850	RPM	sensed PMG voltage greater than 105 volts RMS
Speed	Backup start disconnect initiation speed (A37)	about 850	RPM	PMG voltage greater than 105 volts RMS
Speed	Engine idle governed speed	800	RPM	Engine idle function enabled
Speed	Idle speed	800 ±100	RPM	idle mode (default 800 RPM)
Speed	Idle speed adjustment range	800 ±100	RPM	Default value 800 RPM
Speed	OVERSPEED shutdown	115% ±1% of nominal
Temperature	EGT in exhaust manifold ahead of turbocharger (maximum)	1375	°F (746°C)	full load
Temperature	HIGH COOLANT TEMP shutdown trip point	223° F (106° C) - standby or 215° F (102° C) - prime
Temperature	HIGH COOLANT TEMP warning limit	215° F (102° C) - standby or 207° F (97° C) - prime
Temperature	High coolant temperature shutdown	212	°F (100°C)	standby or primary
Temperature	High coolant temperature warning	202	°F (94°C)	standby or primary
Temperature	LOW COOLANT TEMP warning	70° F (21° C) or lower
Temperature	Low coolant temperature warning	70 or lower	°F (21°C)
Torque	Adaptor-to-engine bolts	35	ft-lbs (48 Nm)
Torque	Diode pigtail terminals	24	in-lbs (2.7 Nm)
Torque	Drive disc-to-flywheel bolts	50	ft-lbs (67 Nm)
Torque	Drive disc-to-rotor bolts	190	ft-lbs (257 Nm)
Torque	Exciter stator mounting screws	7	ft-lbs (10 Nm)
Torque	Generator end plate mounting bolts	25	ft-lbs (34 Nm)
Torque	Generator mounting bracket bolts (M10)	35	ft-lbs (47 Nm)
Torque	Generator mounting bracket bolts (M12)	65	ft-lbs (88 Nm)

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
Fuel	Natural Gas (NG) or HD-5 Propane (LP)				Gas supply pressure max 20 inches WC and min 10 inches WC at full load; NG mixer side 4 to 6 inches WC at 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.

Fault codes

Code	Name	Meaning	Severity	Action
101	IDLE MODE	Indicates that the engine is operating in idle mode; generator build-up is inhibited and engine governed at 800 RPM.	Warning	Remove ground from the engine idle input to return to normal speed and voltage.
102	EMERGENCY STOP	Indicates local or remote Emergency Stop.	Shutdown	Turn the switch clockwise and allow it to pop out (local only); move Run/Off/Auto switch to Off; press the Reset switch; select Run or Auto as required.
200	LOW OIL PRESSURE	Indicates engine oil pressure has dropped to an unacceptable level.	Warning	If powering critical loads, wait until next shutdown period then follow 201-SHUTDOWN procedure. Access Oil Pressure menu prior to clearing the fault.
201	LOW OIL PRESSURE	Indicates engine oil pressure has dropped below the shutdown trip point.	Shutdown	Check oil level, lines and filters; replenish if low; reset control and restart. Oil pressure limits in Table 4-3.
204	OIL PRES SENDER	The control has sensed that the engine oil pressure sender is out of its working range.	Warning	Check that the engine oil pressure sender is properly connected.
210	LOW COOLANT TEMP	Warning occurs when engine coolant temperature is 70°F (21°C) or lower.	Warning	Check coolant heater power supply, coolant level, and heater element.
211	HIGH COOLANT TEMP	Indicates coolant temperature is getting close to the recommended maximum limit (202°F / 94°C).	Warning	Reduce load if possible; check air inlets/outlets; follow 212-SHUTDOWN procedure if engine can be stopped.
212	HIGH COOLANT TEMP	Indicates the engine has overheated (coolant above 212°F / 100°C).	Shutdown	Allow engine to cool; check cooling airflow, fan belt, coolant mixture, blower fan/circulation pumps; reset control and restart.
213	COOLANT SENDER	Resistance of the coolant temperature sender is out of range.	Warning	Check the resistance of the sender; should be 500 to 2k ohms.
214	LOW COOLANT LVL	Indicates engine coolant level has fallen below the trip point.	Warning	Check coolant level in radiator and coolant recovery bottle; look for leakage; reset control and restart.
215	LOW COOLANT LVL	Indicates engine coolant level has fallen below the trip point.	Shutdown	Check coolant level in radiator and bottle; check coolant bottle hose or radiator cap; reset control and restart.
220	MAG PICKUP	Mag pickup speed indication is not being sensed or does not match generator set output frequency.	Shutdown	Restart and check RPM on the digital display; inspect/adjust MPU.
221	FAIL TO CRANK	Possible fault with control or starting system; engine will not crank.	Shutdown	Check fuse F3 on the Engine Interface board; clean battery cable terminals; recharge or replace battery.
222	OVERCRANK	Possible fuel system problem; engine stops cranking.	Shutdown	Check supply shutoff valve, propane tank, gas pressure, fuel filter, air filter, and ignition; correct flooded engine; reset and restart.
223	OVERSPEED	Indicates engine has exceeded normal operating speed (115% ±1% of nominal).	Shutdown	Check mechanical fuel linkage; monitor PCC duty cycle to isolate A32 or A38.
230	LOW DC VOLTAGE	Indicates battery voltage is below 10 VDC.	Warning	Recharge/replace battery; check battery charger fuse; clean/tighten battery cable connections; check engine DC alternator (12 to 14 VDC); check float level.
231	HIGH DC VOLTAGE	Indicates battery voltage exceeds 16 VDC.	Warning	Check float level on battery charger (lower float level); check engine DC alternator.
232	WEAK BATTERY	Indicates battery voltage drops below 60% of nominal for two seconds during starting.	Warning	Recharge or replace the battery; see 230 LOW DC VOLTAGE.
240	LOW FUEL-DAY	Day tank fuel supply is running low.	Warning	Nature of fault is an optional customer selection.
241	LOW FUEL	Fuel supply is running low.	Warning	Nature of fault is an optional customer selection.
250	EEPROM ERROR	PCC memory error; data corruption of critical operating parameters.	Shutdown	Perform the initial start setup procedure; if the same EEPROM ERROR occurs replace the digital board (A32).
251	EEPROM ERROR	PCC memory error; data corruption of noncritical operating parameters.	Warning	Perform adjustment/calibration procedures and save; if the same EEPROM ERROR occurs replace the digital board (A32).
252	EEPROM ERROR	PCC memory error; data corruption of noncritical operating parameters.	Warning	Verify values/choices selected and repeat save; reset, shut off and restart; if the same EEPROM ERROR occurs replace the digital board (A32).
260	CUSTOMER FAULT 1	Customer-defined input closed to ground; fault function can be programmed to initiate a shutdown or a warning.	Warning	Isolate the source of the signal; check external wiring for short to ground; replace A34 or A32 as indicated.
261	GROUND FAULT	Customer-defined input closed to ground; fault function can be programmed to initiate a shutdown or a warning.	Warning	Isolate the source of the signal; check external wiring for short to ground; replace A34 or A32 as indicated.
262	RUPTURE BASIN	Customer-defined input closed to ground; fault function can be programmed to initiate a shutdown or a warning.	Warning	Isolate the source of the signal; check external wiring for short to ground; replace A34 or A32 as indicated.
263	HIGH GEN TEMP	Customer-defined input closed to ground; fault function can be programmed to initiate a shutdown or a warning.	Warning	Isolate the source of the signal; check external wiring for short to ground; replace A34 or A32 as indicated.
301	HIGH AC VOLTAGE	One or more phase voltages has exceeded 130% of nominal, or has exceeded 110% of nominal for 10 seconds.	Shutdown	Troubleshoot PCC, alternator, regulator module A37, PT/CT module A36, customer interface A34 and analog board A33.
303	LOW AC VOLTAGE	One or more of the phase voltages has dropped below 85% of nominal for 10 seconds.	Shutdown	Check PMG or field wiring, rotating rectifier diodes, overload, and connectors; isolate A37, A31, A32, A36, A34, A33.
313	UNDER FREQUENCY	Indicates engine speed dropped below 90% of nominal for 10 seconds; five seconds before shutdown a Load Dump signal is initiated.	Shutdown	Check fuel supply, intake air supply and load; isolate governor output module (A38), A32 or A31.
320	OVERCURRENT	Indicates generator output current exceeded 110% of rated for 60 seconds.	Warning	Check load and load lead connections.
321	OVERCURRENT	Indicates generator output current exceeded 110% of rated and a PCC time/current calculation initiated shutdown.	Shutdown	Check load and load lead connections.
322	SHORT CIRCUIT	Indicates generator output current exceeded 175% of rated.	Shutdown	Check load and load lead connections.
330	OVERLOAD	Three-phase power output exceeds 105% of standby (or 115% of prime) rating.	Warning	Check load and load lead connections.
335	REVERSE POWER	Indicates improper CT or PT phasing (non-parallel units only).	Shutdown	Check CT / PT wiring; refer to CT Installation in Section 5.

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

Procedures

Adjusting Carburetor Power Valve adjustment

Tools: 0-30 psi gauge, Pyrometer, Oxygen meter, Timing light

Install a 0-30 psi gauge on the intake manifold.
Install a pyrometer in the 1/8 inch pipe tapped hole of the exhaust manifold ahead of the turbocharger.
Install an oxygen meter exhaust gas pickup in a 1/8 inch pipe tapped hole of the exhaust elbow.
With the genset at full load, adjust the power valve for the lowest possible exhaust temperature while observing O2.
Turn the power valve closed (toward L) until the engine starts losing RPM.
Then turn the power valve open (toward R) until the exhaust temperature reaches the lowest reading.
LP vapor only: if O2 cannot be set with the power valve, set power valve to mid-point and use the course adjustment valve.

Adjusting Engine Timing adjustment

⚠ DO NOT switch from position 7 to 0, or 0 to 7 while the engine is running.

Tools: Timing light

Connect the timing light high tension lead to the No. 1 spark plug (front cylinder).
Start the genset.
Point the adjustable timing light toward the pointer and TDC mark on the crank pulley.
Remove the white plastic cap and turn the timing switch adjustment screw (10 degree range) of the CD1 Ignition Module.
Switch position 7 gives the most advanced timing; timing retards 1.4 degrees per switch position toward 0 (full retard).
Allow a short delay between each timing position change.
Perform the Carburetor Power Valve Adjustment procedure.

Adjusting Gas Regulator For NG Pressure adjustment

⚠ High gas supply pressure can cause gas leaks which can lead to fire and severe personal injury or death.

Tools: Manometers

Install the manometers into the two test ports of the gas regulator.
Remove the regulator dust cap.
Start the genset and run at full load.
Turn the adjusting screw until the meter shows the appropriate gas pressure for NG on the mixer side.
Turn the screw clockwise to increase pressure.

Servicing the PMG - Testing diagnostic

⚠ HAZARDOUS VOLTAGE. Touching uninsulated high voltage parts inside the control and power output boxes can result in severe personal injury or death.

Tools: Wheatstone bridge or digital ohmmeter

Disconnect leads P2, P3 and P4 from the voltage regulator.
Start the engine at the set and let the speed stabilize.
Measure voltage across lead pairs P2-P3, P3-P4 and P4-P2 (at least 150 VAC for 50 Hz, at least 180 VAC for 60 Hz).
If voltages are low or uneven, check all leads and connections before disassembling the PMG.
Stop the set and measure electrical resistance across P2-P3, P3-P4 and P4-P2 (approximately 4.4 ohms each winding).

Surge Suppresser Testing and Replacement diagnostic

Tools: Ohmmeter

Remove the suppresser.
Replace the suppresser if it appears to have overheated.
Replace the suppresser if ohmmeter readings indicate less than infinite resistance in both directions.
Torque the terminals to 24 in-lbs (2.7 Nm) when reassembling.

Testing Diodes diagnostic

⚠ Layers of dust can cause diodes to overheat and fail.

Tools: Ohmmeter

Disconnect the diode pigtails from the terminal posts.
Measure electrical resistance between each diode pigtail and the plate on which the diode is mounted.
Reverse the meter test probes and repeat the tests.
Replace the diode if resistance is high or low in both directions.

Testing the Exciter Stator diagnostic

Tools: Wheatstone bridge or digital ohmmeter

Measure winding resistance with a Wheatstone bridge or digital ohmmeter.
Replace the stator if winding resistance is not as specified in Table 6-1.
Disconnect the exciter stator leads from terminals X and XX.
Measure resistance between either lead and the stator laminations.
Replace the stator if insulation resistance is less than 1 megohm (1,000,000 ohms).

Testing the Float Switch Assembly diagnostic

Tools: Ohmmeter, Feeler gauge

Remove the fuel pump control cover, disconnect the wiring jack and unscrew the assembly from the top of the day tank.
With an ohmmeter, test for continuity (switch closed) between each pair of colored leads while holding the assembly vertical; replace if any switch is open.
Lift each float in turn to 1/8 inch (3 mm) below the C-clip stop above it and test for continuity; replace if any switch does not open.
Use pipe thread sealant when replacing the assembly.

Testing the Generator Stator and Rotor Windings diagnostic

⚠ Disconnect the starting battery cables (negative [-] first) to make sure the engine will not start while performing these tests.

Tools: Wheatstone bridge or digital ohmmeter (0.001 ohm precision), Megger or insulation resistance meter

Disconnect battery cables (negative first) so the engine will not start.
Measure winding resistance with a Wheatstone bridge or digital ohmmeter and compare to Table 6-1.
Measure winding insulation resistance between leads and laminations; replace if less than 1 megohm.
For the main stator, measure across each pair of stator leads (U1-U2, U5-U6, V1-V2, V5-V6, W1-W2, W5-W6).

Testing the Rotating Rectifier Assembly Diodes diagnostic

⚠ Layers of dust can cause diodes to overheat and fail. Brush dust off regularly.

Tools: Ohmmeter

Disconnect the diode pigtails from the terminal posts.
Measure electrical resistance between each diode pigtail and the plate on which the diode is mounted.
Reverse the meter test probes and repeat the tests.
Replace the diode if resistance is high or low in both directions.

Current Transformer (CT) Installation installation

⚠ Improper installation of CTs will cause a 335 Reverse Power shutdown error (non-parallel units only).

Orient the CT dot toward the generator (conventional current flowing into the dot); dot also indicates pin 1.
CT21 for U load leads (A phase).
CT22 for V load leads (B phase).
CT23 for W load leads (C phase).
6 lead generator sets: route generator output leads through the CTs.
12 lead generator sets: route load wires through the CTs.
For 12-lead (dual secondary) CTs connect secondary wire 1 to pin 1; wire 2/3 to pin 2 (high voltage) or pin 3 (low voltage).

Magnetic Speed Pickup Unit (MPU) Installation installation

⚠ Do not use fan blade to bar over engine.

Bar the engine until a gear tooth on the flywheel lines up in the center of the mounting hole.
Thread the sensor in gently by hand until it just touches the gear tooth.
Back it out one quarter turn and set the locknut.

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

Which generators use the 6C engine?

The 6C powers 1 generator set(s), including Cummins/Onan 3100 series.

What is a common problem with the 6C engine?

A commonly reported issue on generators using the 6C is: WEAK BATTERY.