Kohler generator code Low Coolant Level
High severity — The coolant level sensor in the expansion tank detected coolant below the safe minimum, and the controller shut the unit down to prevent engine damage from overheating.
Applies to: Kohler liquid-cooled standby generators (RCA/RCL series) with an RDC2 controller and a coolant level sensor in the expansion tank
What it means
Wondering why a generator with a coolant reservoir that looks fine at a glance still threw this fault? The sensor Kohler uses for it lives inside the expansion tank itself, not on the main radiator, so it's reading the level in that smaller tank specifically rather than the cooling system as a whole. On RCA and RCL liquid-cooled models, once that sensor reports coolant below its safe minimum, the RDC2 controller shuts the unit down right away. This fault exists purely to stop an engine from running low on coolant long enough to overheat — by the time an actual High Engine Temperature fault would trigger, some damage may already be underway, so Kohler catches the coolant level problem a step earlier instead.
Most common causes
Coolant doesn't just disappear on its own, so this fault usually traces back to one of:
- Coolant leak in hoses, radiator, or water pump
- Air trapped in the cooling system after recent service
- Loose or failed radiator/reservoir cap
- Faulty coolant level sensor giving a false reading
What you can check yourself
Steps that are safe once the unit has fully cooled:
- Once cool, visually check the coolant reservoir level against its fill marks
- Inspect visible hoses and the radiator for leaks or wet residue
- If topping off, use the coolant type specified in the owner's manual — never mix incompatible coolant types
Never crack open a hot cooling system to check any of this — let the unit sit until it's genuinely cool first, since pressurized hot coolant can cause serious burns on contact.
All codes for this brand
Every Kohler generator fault code — full list with what differs between models.
Related codes: High Engine Temperature and EngineSpeed Low. See the Generator Runs Then Shuts Down symptom page for the broader troubleshooting picture.