P0128: Coolant Thermostat Below Thermostat Regulating Temperature
Can you still drive? Yes, this is a low-severity code. The engine will run slightly cooler than optimal, which reduces fuel efficiency but is not dangerous.
What Does P0128 Mean?
Code P0128 indicates that the engine coolant temperature has not reached the expected operating temperature within a specified time after starting. This typically means the thermostat is stuck open, allowing coolant to flow continuously through the radiator and preventing the engine from warming up properly.
Need to read your codes?
An OBD-II scanner lets you read and clear diagnostic trouble codes from your vehicle's computer. Most scanners work with any car made after 1996.
Browse OBD-II Scanners on AmazonCommon Causes
- Stuck-open thermostat
- Faulty engine coolant temperature sensor
- Low coolant level
- Thermostat housing leak
Symptoms
- Check engine light on
- Temperature gauge reads lower than normal
- Heater blows lukewarm air
- Slightly reduced fuel economy
Diagnostic Steps
- 1Check coolant level and condition
- 2Monitor coolant temperature with scan tool during warm-up
- 3Compare actual coolant temp to gauge reading
- 4Test thermostat operation by monitoring coolant flow
- 5Inspect thermostat housing for leaks
Recommended Parts & Tools
engine coolant temperature sensor
Estimated Repair Cost
| Type | Estimated Cost |
|---|---|
| Total Repair Cost Range | $50 - $400 |
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Chat with AI About P0128Commonly Affected Vehicles
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Frequently Asked Questions
Is P0128 serious?
P0128 is low severity. It typically means the thermostat is stuck open. Your car is safe to drive but fuel efficiency and cabin heating will be reduced.
How much does it cost to replace a thermostat?
A thermostat replacement typically costs $150-$300 at a shop. The part itself is $20-$50 and labor is about 1-2 hours.
Community Fix Reports
Community reports are user-submitted and not verified by Auto AI Buddy. Results may vary.
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