P0126 means Insufficient Coolant Temperature for Stable Operation. The engine is taking too long to reach the temperature the computer needs for normal fuel control. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What P0126 means
The coolant temperature reading feeds many systems: warm-up fueling, ignition timing, idle speed, cooling fan control, transmission shift timing and often the dash gauge. A wrong reading causes symptoms far beyond the cooling system, and a real overheat can damage an engine quickly. Confirm the actual temperature with a scan tool or an infrared thermometer before replacing parts.
P0126 symptoms
- Temperature gauge reading low
- Weak cabin heat
- Poor fuel economy
- Check engine light
Common causes of P0126
- Thermostat stuck open
- Coolant temperature sensor reading low
- Low coolant level
How to diagnose P0126
- Watch coolant temperature on a scan tool during a drive
- Check the coolant level
- Test the thermostat
Can you drive with P0126?
Yes, but fix it to restore heat and fuel economy.
P0126 tips
A thermostat stuck open is the usual cause; it often sets P0128 at the same time. On engines with an electric or controlled thermostat, check its control circuit as well as the thermostat itself, and confirm the cooling fans are not running all the time.
Will P0126 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P0126 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| P0128 | Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) |
| P0125 | Insufficient Coolant Temperature for Closed Loop Fuel Control |
| P0117 | Engine Coolant Temperature Sensor 1 Circuit Low |
Guides that help
When it is more than a sensor
Most cooling codes end with a thermostat, sensor, fan or leak repair. If the engine overheated badly enough to fail the head gasket or warp the heads, compare a repair against a replacement on our engines page and read engine replacement cost.
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