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Dodge Challenger P0128: Coolant Thermostat – Under Temperature


P0128 is a relatively common OBDII fault code. It is activated when your Dodge Challenger coolant temperature does not reach the proper operating temperature.

Dodge Challenger P0128

It is a generic powertrain code, meaning that regardless of who manufactured the vehicle, it will have the same meaning (1996+).

Challenger P0128 Symptoms

There are not many symptoms with P0128 unless it gets cold. These are the symptoms associated with this fault code:

  • Lack of heat– The biggest symptom of the P0128 fault code on the Dodge Challenger is going to be a lack of heat. When the thermostat does not bring the engine up to proper operating temperature, it means that the water passing through the heater core is not as hot. This results in less/no heat.
  • Engine service soon– Other than the heater not working as well, the only other symptom of P0128 is usually the check engine light itself.

P0128 Causes: Dodge Challenger

P0128 Dodge Challenger

Fixing P0128 is usually a fairly easy thing to do, since 90% of the time it will be the thermostat that throws the code. Here are the most common causes of P0128:

  • Thermostat stuck open– The most typical cause of the P0128 code is a stuck thermostat. When the thermostat is stuck, it allows coolant to flow through the engine at all times. When this occurs, the engine is “supercooled” and never reaches the proper operating temperature. How to replace a thermostat (video). Challenger Thermostat
  • Cabling– If the thermostat itself is not the problem, it will be the wiring/sensor associated with detecting the engine water temperature, or the coolant temperature sensor itself.

Dodge Challenger Diagnostics P0128

A good way to tell if it is a sensor or thermostat problem is going to be whether the engine is running at the proper temperature or not. It can be very difficult to know this in a vehicle that does not have a temperature gauge.

A good way to at least get an idea of ​​whether or not it is the thermostat or the sensor is to start the car cold and let it idle for about ten minutes. If you feel little or no heat from the heater, then it is a good indication that the thermostat is the problem and not a wiring problem.

Additionally, a mechanic will often check under the hood where the radiator hose joins the thermostat housing. If the hose is easy to pinch, water will normally flow through it. If you pinch the hose, make sure you account for the strap-on accessories and the fan. The fan can be turned on at any time.


P0128 is not a serious threat to the immediate drivability of your Challenger. Keep in mind that most modern fuel-injected engines run at over 200 degrees. Letting them run too cold can cause problems after a long period of time. Good luck figuring out what’s wrong with your Challenger.


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