how to fix the P0128 code on my Volkswagen Passat B8 (2015-2022)

Learn how to diagnose and fix P0128 cooling system issue in Volkswagen Passat B8 (2015-2022). Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative terminal of the battery.
• Ensure the engine is cool before starting.

2. Inspect and Replace the Thermostat

• Sub-steps:
  1. Drain the engine coolant into a clean container.
  2. Remove the thermostat housing (usually involves removing bolts with a socket set).
  3. Carefully remove the old thermostat from the housing.
  4. Clean the mating surfaces of the housing and engine to ensure a good seal.
  5. Install the new thermostat in the correct orientation as per the manufacturer's specifications.
  6. Reattach the thermostat housing and torque bolts to the manufacturer's specified values (typically around 10-15 Nm).

3. Replace the Coolant Temperature Sensor (if faulty)

• Sub-steps:
  1. Locate the coolant temperature sensor on the engine.
  2. Disconnect the electrical connector.
  3. Remove the sensor using an appropriate socket.
  4. Apply a small amount of thread sealant on the new sensor threads.
  5. Install the new sensor and reconnect the electrical connector.

4. Refill and Bleed the Cooling System

• Sub-steps:
  1. Refill the cooling system with the appropriate type of coolant as specified in the owner’s manual.
  2. Start the engine and allow it to reach operating temperature while keeping the radiator cap off.
  3. Monitor for any air bubbles escaping; top off coolant as needed.
  4. Once the engine reaches temperature and the thermostat opens, check the coolant level and top off if necessary.

5. Reconnect Battery and Clear Codes

• Sub-steps:
  1. Reconnect the negative terminal of the battery.
  2. Use the OBD-II scanner to clear the P0128 code.
  3. Start the vehicle and monitor for any reoccurrence of the code.