P0128Cars & SUVs
EasyP0128 — Coolant thermostat — temperature below regulating range
The engine takes too long to reach operating temperature—or never gets there. Very common when the thermostat sticks open after several winters.
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Likely causes
- Thermostat stuck open
- Faulty engine coolant temperature (ECT) sensor
- Cooling fan running continuously
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Recommended checks
- 1
Replace the thermostat with an OEM-temperature unit
- 2
Verify the ECT sensor against actual coolant temperature
- 3
Check the fan relay and fan operation
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Parts to replace
Thermostat
Thermostat gasket
ECT sensor