Kohler Generator Fault Messages (RDC2)

Kohler shows messages, not numbers

Kohler's RDC2 and DC2 controllers, used on 14/20RESA, 14/20RESAL, 20RESC and 20RESCL home generators, display a short text message when something is wrong, such as "Over Crank" or "Oil Press Low". Kohler's operation manual lists those messages; it does not list numbered fault codes. If you are looking up a Kohler code number you found online, look up the message on your controller's screen instead.

Warnings and shutdowns

Every message is either a warning or a shutdown. On a warning the controller shows the message but the generator keeps running, and the message clears by itself once the condition is corrected. On a shutdown the generator stops, the OFF light flashes, and it cannot restart until the problem is fixed and the controller is reset. Kohler notes that shutdown switches such as the low oil pressure switch reset themselves when the problem is corrected, but the fault on the controller does not clear until you reset it.

Message	Type	What triggered it	Kohler's check
Over Crank	Shutdown	Three unsuccessful starting attempts	Fuel supply, spark plug and battery; loose connections; then a dealer
Oil Press Low	Shutdown*	The low oil pressure switch reads low for more than 5 seconds (active 30 seconds after the engine starts)	Oil leaks, oil level, the oil pressure switch and its wiring
Locked Rotor	Shutdown	No engine rotation sensed during cranking; shuts down 3 seconds after it is detected	Battery and loose connections; then a dealer
Spd Sens Flt	Shutdown	Engine speed sensor failed, or the engine stalled	Dealer
Eng Speed High	Shutdown*	Engine speed above 115% of normal for more than 0.3 seconds	Dealer
Eng Speed Low	Shutdown*	Engine speed below 85% of normal for more than 3 seconds	Reduce the load; on 20RESC/20RESCL check the enclosure thermostat; then a dealer
Frequency High	Shutdown*	Frequency above 110% of the setpoint for more than 10 seconds	Dealer
Frequency Low	Shutdown*	Frequency below 90% of the setpoint for more than 10 seconds, or 1 Hz low for more than 60 seconds	Reduce the load and restart; on 20RESC/20RESCL check the enclosure thermostat; then a dealer
Volts L1-L2 High	Shutdown*	Output voltage above 120% of nominal for more than 2 seconds	Dealer
Volts L1-L2 Low	Shutdown*	Output voltage below 80% of nominal for more than 10 seconds	Reduce the load and restart; on 20RESC/20RESCL check the enclosure thermostat; then a dealer
AC Sens Loss	Warning after 1 s, shutdown after 3 s*	Generator AC output sensing lost in Auto mode	Dealer
MainPwrOverL	Shutdown	Short circuit (over-current) on the controller power output	Dealer
Accy PwrOver Warning	Warning	Short circuit (over-current) on the accessory power output	Dealer
Aux Input	Shutdown*	An optional customer-connected input is closed	The customer-supplied equipment wired to that input
Battery CrLo Warning	Warning	Starting battery below 11 V for more than 10 seconds (not checked while cranking)	Battery rating and condition, the battery charger; charge or replace the battery
Battery Voltage Low	Warning	Starting battery below 12.5 V for more than 90 seconds with the engine stopped	Battery rating and condition, the battery charger; charge or replace the battery
Battery High	Warning	Starting battery above 16 V for more than 10 seconds	Battery rating and condition, the battery charger
Lo Crank Vlt	Warning	Battery below 8 V for more than 6 seconds while the starter is engaged	Charge or replace the battery
Batt Chg Flt	Warning	Fault signal from an external battery charger (not the built-in one)	The external battery charger
ATS ComError	Warning	Communication with the transfer switch interface lost	Communication wiring between the transfer switch interface board and the generator
ATS PhaseRot	Warning	Transfer switch phase rotation does not match; the switch will not transfer	The transfer switch connection, per its installation manual
Not in Auto	Warning	Not in Automatic (standby) mode, so remote start and stop commands are ignored	Press AUTO
Exer Not Sch	Warning	No exercise is scheduled on the controller	Set the exerciser
Advanced Diagnostic	Shutdown (event history only)	Shutdown during the reduced-speed part of an exercise; the engine restarts, runs at full speed for 2 minutes and stops	If it does not restart and return to AUTO, check for other faults

Reading the table

Shutdowns marked * run the engine cooldown before stopping. Kohler also notes that a low battery can trigger a low coolant level fault on air-cooled models, so check the battery first if both appear. The 20RESC and 20RESCL notes refer to the enclosure thermostat, which Kohler says to check and reset if tripped.

Oil Press Low does not mean the oil level is fine

Kohler's manual makes a point worth repeating: the low oil pressure shutdown does not protect against low oil level. An engine can run low on oil before the pressure drops, so check the oil level on the schedule in your operation manual rather than relying on the shutdown.

Resetting after a shutdown

Find and fix the cause first. Then press OFF to reset the controller, or use the menu: with the message showing, press Select to reach the overview, press Select again to show the active fault, press Select to see "Confirm Clear Fault: NO", change it to YES with the arrow button, and press Select. The controller goes to OFF; press AUTO to return the generator to standby. Kohler's advice for most engine, speed and voltage shutdowns is to contact an authorized distributor or dealer if the message returns.

Frequently Asked Questions

What do Kohler generator fault codes mean?

On Kohler RDC2 and DC2 home generators the controller shows a text message, not a number. The table above lists every message in Kohler's operation manual, what triggers it, and Kohler's check.

What does Over Crank mean on a Kohler generator?

Three unsuccessful starting attempts. Kohler says to check the fuel supply, spark plug, battery and loose connections, then call a dealer.

Will my Kohler generator keep running with a warning?

Yes. A warning shows a message but the generator keeps running, and the message clears once the condition is corrected. A shutdown stops the generator until you fix the cause and reset the controller.

Sources

Documents this guide was checked against. How we verify.

Kohler Home Generator Fault Messages: What Each One Means (RDC2 and DC2)