P0128 - OBD Trouble Code

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The OBD P0128 code means that the engine coolant is not warming up enough and fast enough. To rephrase, there is a glitch with the engine functioning temperature that is not being reached within a specific time frame. The Engine Control Module (ECM) dictates this measure of time based on the relation of temperature.

What causes this problem with the Coolant Thermostat?

• Below average engine coolant level
• Thermostat is likely stuck open or leaking
• Defective cooling fan (running too much)
• Defective coolant temperature (ECT) sensor
• Defective intake air temperature (IAT) sensor

1. Engine Coolant Level - A coolant leak causing a poorer coolant level is a common issue. Since the coolant main purpose is to cool down the engine parts, if there is a lack of quality in the coolant amount, it will not cool down the engine components, which causes the engine to overheat.
   As a conclusion, make sure you get just the right amount of coolant for your car’s command.
2. Thermostat - A thermostat that is overheated can obstruct the correct function of engine controls and accelerate the engine’s performance temperature to a degree that it gets a spark knock experience. If installing a colder thermostat, make sure the coolant is hot enough to target the correct control performances, or it will enable the computer system to go into a closed loop.
3. Engine Control Module - Your car might not start even after making sure that its battery and starter are working correctly. If your car's problems narrow down to a defective engine control module, you should replace it as soon as possible to prevent further severe risks to your car.
4. Ambient Temperature Sensor - This type of sensor can’t be adjusted or fixed, but if it gets broken, it must be replaced. Get the best replacement for your ambient temperature sensor so you can continue to be aware of the exact temperature outside of your car, even in the winter season.
5. Coolant Temperature Sensor - A defective sensor can emit black smoke from the exhaust pipe, as gas is being used too much. Your ride may have complications starting after it has reached its typical functional temperature, or if your coolant temperature gauge changes irregularly. The rightful coolant temperature sensor for your car can exceed issues with overheating, assuring a safer and smoother ride.
6. Intake Air Temperature Sensor - The computer of a damaged IAT sensor may send the wrong amount of fuel, interrupting the balance in the air-fuel mixture and causing a lot of driving problems by rich or lean mixtures. Avoid this by getting a new IAT sensor as soon as possible.

If you ask any mechanic about a P0128 code, many of them will explain to you the thermostat is the problem. A majority of the time, they will be right. These following symptoms of a dysfunctional thermostat are as follows:

Common Symptoms

• Detect Engine Light On
• At freeway speed car may not shift to highest gear
• Decline in fuel economy
• It may be an unusual case if no harmful conditions are noticed by the driver

Before replacing the thermostat, check for all the possible causes, such as the condition of the cooling system for any rust deposits or mixture of various coolants. Be sure to flush the engine block and radiator when restoring the thermostat to prevent deposits from getting jammed in the new thermostat.

• Exchanging the thermostat (most common repair)
• Exchanging the coolant temperature sensor, or the wiring and connector related with the sensor that is being damaged.

For an accurate diagnosis, you need a scan tool, but it's also possible to receive a reading if your car a has a temperature gauge. You need to compare this reading to one obtained by an infrared thermometer. The thermometer should normally provide a temperature around 200 degrees Fahrenheit. If the scan tool reading does not pair closely with the thermometer, then the sensor side of the car has a problem.

• To start with, check to ensure that the engine is contained with enough suitable coolant so that the thermostat is performing accurately
• Start your diagnosis by watchfully checking for all wiring and connectors
• View for wiring that is shorted or burned and exchange circuitry and connectors as needed
• Suppose if the system wiring, connectors, and components look to be working in normal order, connect the scanner to the diagnostic connector and record all retained trouble codes and freeze frame data
• This data can be immensely helpful in diagnosing irregular conditions that could have provided to this code being retained
• After clearing the codes, run the car to see if the code comes back
• If the code fails to return instantly, you might have an irregular condition
• Irregular conditions can uphold as being such a challenge to diagnose and in intense cases may need be enabled to worsen before precise diagnosis is able be made. Detect the fan clutch (if equipped)
• This code is often set because the driver does not enable adequate engine heat up time (especially in cold weather)
• It is a good idea to reset the code and see if it comes back when this code is on display

Common Mistakes When Diagnosing The P0128 Code

Exchanging the thermostat without detecting the car:

If ever making an inquiry about P0128, up to 9 out of 10 mechanics will tell you the thermostat is defected. On a long stretch, the mechanics could be right. Regardless, at certain times it is possible that the thermostat will not be able to fix this code.