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).

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

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Rubbing noise from driver's front wheel while turning right

Look at the inner fender or track arm for signs of the tire rubbing on the parts. Your tires may be a little too wide for your vehicle. The fix may be to swap for a narrower tire. Also be...

Q: Engine will not stay started. I have replaced idle control valve map sensor spark plugs spark plug wires no check engine light is

You have a problem with the distributor assembly. I recommend replacing the distributor assembly. This will replace all the possible sensors and coil for the ignition and fix the problem you have.

Q: I got a quote for $900+ to replace two thermostats, 2 hoses, and flush the radiator. Is there 2 thermostats? Is this kosher?

Hi there. Yes on the 2009 Jeep Patriot there are two thermostats. There is a thermostat for the main engine cooling system and a thermostat for the cylinder head cooling system. If you need assistance with changing out the thermostats,...

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...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...