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Engine-Codes – GMC – P0128 GMC

P0128 GMC Code - Engine Coolant Temperature Below Thermostat Regulating Temperature

Quick Answer

The P0128 error code for GMC vehicles indicates that the engine coolant temperature is below the thermostat regulating temperature. Common causes include Malfunctioning thermostat, Faulty coolant temperature sensor, Low coolant level. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means
P0128 GMC indicates Engine Coolant Temperature Below Thermostat Regulating Temperature.
Common causes
Common causes include Malfunctioning thermostat, Faulty coolant temperature sensor, Low coolant level.
Severity
High - diagnose this code as soon as possible.
Can I drive?
Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
What is this?
Table of contents Created and updated by William Orellana on Sep 07, 2024
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Code P0128 GMC Description

The P0128 error code for GMC vehicles indicates that the engine coolant temperature is below the thermostat regulating temperature. The thermostat is a crucial component of the engine cooling system that helps regulate the temperature of the engine by controlling the flow of coolant through the engine. When the engine coolant temperature falls below the specified range set by the thermostat, it triggers the P0128 code.

OBDII Code P0128 GMC - Engine Coolant Temperature Below Thermostat Regulating Temperature
P0128 GMC Code - Engine Coolant Temperature Below Thermostat Regulating Temperature

Common Causes of P0128 GMC

  1. Malfunctioning thermostat
  2. Faulty coolant temperature sensor
  3. Low coolant level
  4. Clogged radiator
  5. Malfunctioning water pump

Symptoms of P0128 GMC

  1. Engine running colder than normal
  2. Decreased fuel efficiency
  3. Check Engine Light illuminated
  4. Poor engine performance
  5. Sluggish acceleration

How to Fix P0128 GMC

  1. Check the coolant level and top up if necessary.
  2. Test the thermostat to ensure it is opening and closing properly.
  3. Inspect the coolant temperature sensor for any signs of damage or malfunction.
  4. Flush the radiator to remove any debris or contaminants that may be causing a blockage.
  5. Replace the water pump if it is not functioning correctly.

Cost to Fix P0128 GMC

The cost of repairing a P0128 code can vary depending on the specific cause of the issue. On average, the cost of parts and labor for this repair can range from $150 to $500. It is important to note that the actual cost may vary based on factors such as location, vehicle make and model, and the extent of the repair needed. Additionally, diagnosis time and labor rates at auto repair shops can also impact the final cost. It is recommended to consult with a qualified mechanic or auto repair shop for a more accurate estimate based on your specific circumstances.

What does this mean?

Tech Notes for P0128 GMC

If the cooling system is not leaking and the fluid level is OK, replacing the thermostat usually takes care of the problem.

Need more information about the P0128 GMC code?

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Need Help with the Code?

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Information for Specific GMC Models

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P0128 GMC Code

1. What are the common symptoms of OBDII code P0128 in a GMC vehicle?

- Common symptoms include the engine running colder than normal, poor fuel economy, and the Check Engine light being illuminated.

2. What typically causes the OBDII code P0128 in a GMC vehicle?

- The most common cause is a malfunctioning thermostat, which fails to regulate the engine coolant temperature properly.

3. How serious is the OBDII code P0128 in a GMC vehicle?

- While it may not cause immediate harm to the vehicle, it can lead to reduced fuel efficiency, increased emissions, and potential damage to the engine over time.

4. Can a faulty coolant temperature sensor trigger the OBDII code P0128 in a GMC vehicle?

- Yes, a faulty coolant temperature sensor can sometimes be the cause of the P0128 code, as it may provide incorrect temperature readings to the engine control module.

5. What are some DIY repair tips for resolving the OBDII code P0128 in a GMC vehicle?

- DIY repair tips include checking and replacing the thermostat, ensuring proper coolant levels, and inspecting the cooling system for leaks or blockages.

6. How can a mechanic diagnose the OBDII code P0128 in a GMC vehicle?

- A mechanic can use a scan tool to read the code, test the thermostat for proper operation, check the coolant temperature sensor, and inspect the cooling system components.

7. Is it safe to continue driving with the OBDII code P0128 in a GMC vehicle?

- It is generally safe to drive with the P0128 code, but it is recommended to address the issue promptly to prevent potential engine damage and ensure optimal vehicle performance.

8. Will resetting the Check Engine light resolve the OBDII code P0128 in a GMC vehicle?

- Resetting the Check Engine light may temporarily turn it off, but it will not fix the underlying issue causing the P0128 code. The problem should be diagnosed and repaired.

9. How much does it typically cost to repair the OBDII code P0128 in a GMC vehicle at a mechanic or dealership?

- Repair costs can vary depending on the exact cause of the issue, but the average range is between $150 to $400 for parts and labor.

10. Can a clogged radiator or cooling system cause the OBDII code P0128 in a GMC vehicle?

- Yes, a clogged radiator or cooling system can restrict the flow of coolant and lead to improper temperature regulation, triggering the P0128 code.

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