P0128 — Coolant Thermostat (Below Regulating Temperature)
PowertrainlowThe engine is taking too long to warm up.
Symptoms
- Temperature needle stays low
- Weak heater
- Slightly more fuel use
Common causes
- Thermostat stuck open
- Faulty coolant temperature sensor
- Low coolant
How to fix
- Check coolant level
- Compare sensor reading with real engine temperature
- Replace the thermostat
Can I keep driving?
Yes.
These are the general meanings. Some companies use a code a little differently — confirm with a scanner and your car's service manual.