What Is the P0128 Code?
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Error code P0128 simply means the coolant temperature is below the ability of the thermostat to regulate. This code may not alert you to the exact nature of the problem, however, it can be an indication of several issues you should check out as soon as possible.
More About Error Code P0128
OBD codes are a result of your On-Board Diagnostic System (OBD) detecting mechanical malfunctions with your vehicle. There are two forms of P codes: P0 and P1. P0 codes are related to the vehicle’s powertrain/emissions system, whereas P1 codes are not emissions-related and therefore don’t cause the check engine light to come on, which is a common symptom of a P0128 code.
P0128 is an extension of OBD-II code P0 which indicates a problem with your car’s coolant thermostat. P0 codes are displayed as P0XXX, with the third numeral in the code sequence signifying where the system has encountered a problem. The number 1 after P0 indicates a problem with fuel and air metering, which may indicate that there’s a malfunction with your thermostat.
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What Are the Symptoms of a P0128 Code?
The most common sign regarding error code P0128 is the check engine light turning on. Other symptoms include your car taking longer to warm up, the temperature rising while driving on the highway, or the temperature gauge indicating your engine is cooler than it should be.
Other symptoms of error code P0128 include the heater no longer working as it should, reduced fuel economy, or a failed emissions test if applicable.
What Are Some Causes of a P0128 Code?
Error code P0128 indicates that your engine coolant temperature is below the thermostat regulating temperature. This means that your Engine Control Module (ECM) or Powertrain Control Module (PCM) has recognized that your engine is running cooler than it’s supposed to. When the engine runs cooler than it should, the temperature doesn’t increase fast enough. This can cause problems with fuel economy and controlling emissions.
Causes of a P0128 code include:
- A bad coolant temperature sensor
- The cooling fan is stuck on
- A bad intake air temperature sensor
- A thermostat that’s malfunctioning or stuck open (electronically controlled or traditional)
A P0128 can also be the result of using your car in a cold climate during the winter and being unable to get to normal operating temperature. Taking several small trips could reset it.
How Serious Is the P0128 Code?
Any time your car’s OBD system triggers an error code it should be taken seriously, particularly one regarding the powertrain such as P0128. As it relates to a P0128 error code, vehicle coolant cools down your car much like how sweat is the body’s natural way of cooling itself. Therefore, when your car reaches a certain temperature, your vehicle’s thermostat should open up and allow coolant to flow through the engine. Code P0128 monitors how fast the coolant reaches a certain temperature rather than tracking if a car is overheating by default. A P0217 code would indicate whether or not the vehicle is overheating. Code P0128 is a fault condition that is gauged against similar codes with the main result being an increased emission level and poor fuel economy.
Can I Still Drive with a P0128 Code?
P0128 isn’t the worst code out there, but you should still have a professional mechanic check your car ASAP. Doing so assures you that your vehicle is always operating at its best, while preventing any additional damage. Ultimately, you should take your car to a nearby mechanic for repairs whenever experiencing a P0 code of any variation.
How Easy Is It to Diagnose a P0128 Code?
Several things can cause error code P0128 to appear, so diagnosing it on your own can prove to do more harm than good. Therefore, it is best to contact a local mechanic for sufficient diagnosis. Most mechanics will check to see how hot the coolant temperature is as it starts to flow through the radiator hose. Generally, the hose needs to be heated until the thermostat is open. When this occurs, hot coolant should start to flow and heat up the radiator hose quickly. If the radiator hose is warming slowly and does not heat up as rapidly as it should, the thermostat may be stuck open. However, if the hose becomes hot too fast, the mechanic will check for issues with the coolant temperature sensor.
To check the coolant temperature sensor, a mechanic will either utilize a scan tool or simply check the car’s temperature gauge. Most vehicles have two separate sensors for monitoring coolant temperature. One of these sensors is used for informing the ECM of the coolant temperature. The second sensor is used as a gauge or warning light on the dashboard to alert the driver of an overheating condition. Manufacturers like Volkswagen actually display a blue coolant light on the dashboard to indicate that the coolant is below regulating temperature.
The temperature from a vehicle’s thermometer should be 200° F if the coolant system is functioning correctly. If the scan tool doesn’t match the thermometer reading, it’s most likely an issue with your coolant temperature sensor. When this happens, the connectors for your sensor are often damaged or deteriorated which will cause a poor connection. If the connectors are fine, this indicates the sensor is at fault.
These methods are very technical and often require the expertise of experienced and qualified mechanics in order to provide a sufficient diagnosis. For the best outcome, it’s advisable that you have your car checked by a professional mechanic to determine the root cause of the error code and perform the necessary repairs.
Need Additional Help with Your P0128 Code?
If you need assistance diagnosing or repairing your car after receiving a P0128 error code, KBB.com can help. Simply check out our list of service centers for locations near you. There you’ll find a mechanic in your area who can diagnose and repair your car based on the error code you received.
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