OBD
P0126
Insufficient Coolant Temperature for Stable Operation
What it means
P0126 means Insufficient Coolant Temperature for Stable Operation.
Check these first
- A thermostat stuck open
- A low coolant level
- A failed engine coolant temperature sensor
- A blocked radiator or hose
- A failing water pump
What to do next
- Check the coolant level and top it off
- Compare the ECT reading to the actual engine temperature
- Replace the thermostat if it is stuck open
- Replace the ECT sensor if the reading is off
- Check the water pump and radiator flow
- Clear the code and retest
Look up another code
Enter a full code or a symptom. Press / to search. How to read a code
Type a code above, or start from a symptom or a common code.
Updated
Generic SAE J2012 definition. Last updated 2026-10-10.