Skip the auto shop - Our mechanics make house calls

Q: Check Engine code P0128

asked by on

The Check Engine light is on with the code P0128 for the coolant thermostat (coolant temperature below thermostat regulating temperature).

A: The cooling system temperature is regulated...

The cooling system temperature is regulated by thermostat, and the cooling fans order to keep it at optimal temperature for the motor to operate. It does this by keeping the thermostat closed and the fans off until the coolant reaches around 195 to 210 degrees then opens the thermostat to cycle the coolant through the radiator while the cooling fans blow through the radiator cooling the coolant. If the thermostat is stuck open then coolant will never stay inside the motor long enough to heat up to the specified temperature. This would set a P0128. To verify that the thermostat has failed a proper inspection of the Check Engine Light should be called out by a qualified technician, like the one from YourMechanic.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%

Get a quote

What others are asking

Q: Check engine light still on after repair. 2006 Infiniti G35

Hello. If the Check Engine Light remained on after the battery was plugged in, then it may be possible that the issue is with the wiring. Faulty wiring or a bad connector to the cam position sensor keeping the Check...

Q: Car stalls after starting

Hello - there are a number of issues that can cause stalling problems after your engine starts, or when you put it into gear. These include a dirty or malfunctioning idle air control valve, an air leak in the intake,...

Q: I have an overheating problem. Its not the fans! With the radiator cap off I can't really see the fluid flowing until I hit the gas.

Hi there - lets look at the behavior overall. Did you replace the clutch fan with electric fans because of an overheating issue? If so, that fundamental issue is likely still present. If temp rises quickly to overheat (matter of...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...