Seeing the P0128 code on your Duramax can be frustrating. The most common reason for this code is a stuck thermostat, causing your engine not to reach the correct operating temperature. Don’t worry, though; you’ll find easy-to-follow steps to fix this issue. Keep reading to learn the causes, how to fix it, and keep your Duramax running smoothly.
Symptoms of P0128 in Duramax
If your Duramax engine is throwing a P0128 code, you might notice a few common symptoms. These indicators can help you understand what’s going on.
High Fuel Consumption: When the engine doesn’t reach the right temperature, it uses more fuel. This results in high fuel consumption.
Temperature Drops at High Speeds: While driving fast, you might see that the engine temperature drops. This can be a clear sign of the P0128 code.
Slow Warm-Up Time: Your engine may take longer to reach its optimal temperature. If it stays cold for too long, it could be a symptom of P0128.
Poor Heating Performance: In colder weather, the heating inside the vehicle might not work well. This happens because the engine isn’t warming up as it should.
Check Engine Light: One of the most obvious signs is the check engine light coming on. This light alerts you to the presence of the P0128 code.
These symptoms can indicate several possible issues, such as a faulty thermostat or a malfunctioning temperature sensor. A more detailed inspection is necessary to pinpoint the exact cause.
Ignoring these symptoms can lead to more serious problems, so addressing them promptly is important. Understanding these warning signs helps keep your vehicle running smoothly and efficiently.
Potential Causes of P0128 in Duramax
The P0128 code in your Duramax can stem from several issues. It often indicates a problem with the thermostat, the coolant levels, or the coolant temperature sensor. Understanding these potential causes can help you diagnose and fix the issue more efficiently.
Thermostat Failures
The thermostat plays a critical role in regulating your engine’s temperature. If it fails, it could cause the P0128 code. Thermostats typically start opening at around 160 degrees Fahrenheit and are fully open at about 180 degrees Fahrenheit, as explained on the Duramax Forum.
A malfunctioning thermostat might not open at the correct temperature, causing the engine to run cooler than expected. This can trigger your vehicle’s engine control module (ECM) to display the P0128 code.
If your thermostat is stuck open, the coolant continuously flows through the radiator, preventing the engine from reaching optimal operating temperatures. Replacing a faulty thermostat could cost between $15 to $300, depending on the model and labor charges.
Coolant Level Issues
Low coolant levels can also cause the P0128 code. When there’s not enough coolant, your engine may not reach the necessary temperature for efficient operation. This is because the coolant helps absorb and dispel heat from the engine.
Inspect your coolant reservoir and radiator. If levels are below the recommended line, top off with the appropriate type of coolant. Leaks can cause low coolant levels. Look for signs of leakage under your car or around the engine bay.
Addressing coolant level issues is usually straightforward. However, if you continually find low levels, it might indicate a more serious issue like a leaking hose or a faulty radiator, which would need immediate attention.
Coolant Temperature Sensor Problems
The coolant temperature sensor (ECT sensor) monitors your engine’s temperature and sends this data to the ECM. If it’s defective, the ECM may incorrectly think the engine is running cooler than it actually is, causing the P0128 code.
A malfunctioning sensor may result in erratic temperature readings. You might also notice other symptoms, like poor fuel efficiency or performance issues. Testing the sensor’s resistance at various temperatures can confirm if it’s working correctly.
Replacing an ECT sensor typically costs between $300 to $320. Regular inspections can prevent issues from affecting your vehicle’s performance.
Solutions to Resolve P0128 in Duramax
When dealing with the P0128 code in your Duramax, addressing the thermostat, the coolant system, and the coolant temperature sensor are key steps. Each of these plays a crucial role in getting your engine running at the right temperature.
Replacing the Thermostat
The thermostat in your Duramax controls the engine’s operating temperature. A faulty thermostat can cause the engine to run cooler than expected, triggering the P0128 code. To replace it, you’ll need to locate the thermostat housing, usually found near the engine block.
Drain the coolant before removing the housing. Once accessed, remove the old thermostat and install the new one. Ensure it’s correctly positioned and reassemble the housing. Refill the system with coolant, and start the engine to check for leaks. A malfunctioning thermostat is often the simplest cause to check first and can be a relatively inexpensive fix.
Refilling and Bleeding the Coolant System
Low or old coolant can affect your engine’s ability to reach the necessary temperature. Start by draining the old coolant. Next, refill the system with a 50/50 mix of antifreeze and water. After refilling, bleeding the system is crucial to remove any air pockets that could cause overheating or cooling issues.
To bleed the system, start the engine and let it run with the radiator cap off. Keep adding coolant as air bubbles escape. This process can take several minutes. Reattach the radiator cap once the bubbles stop. Refilling and bleeding ensure your Duramax’s coolant system operates efficiently, helping to clear the P0128 code.
Replacing the Coolant Temperature Sensor
The coolant temperature sensor (CTS) monitors the engine’s temperature and sends this information to the engine control unit (ECU). If the CTS fails, it could incorrectly signal that the engine is too cold, triggering the P0128 code.
To replace the CTS, locate it near the thermostat housing or radiator. Disconnect the battery before removing the sensor’s electrical connector. Unscrew the old sensor and quickly replace it with the new one to minimize coolant loss. Reconnect the electrical connector and battery. This step ensures your ECU receives accurate temperature readings, clearing the P0128 code and maintaining engine performance.
