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

Learn how to diagnose and fix P0128 code in Volkswagen Passat B8. Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool down completely before starting work.

2. Thermostat Replacement

1. Drain the Coolant:

   • Place a drain pan under the radiator.
   • Open the radiator drain valve and allow coolant to drain.

2. Remove the Thermostat:

   • Locate the thermostat housing (typically near the engine block).
   • Disconnect any hoses attached to the housing.
   • Remove the bolts securing the thermostat housing using a socket wrench.
   • Carefully lift off the housing to access the thermostat.
   • Remove the old thermostat and its O-ring or gasket.

3. Install the New Thermostat:

   • Clean the mating surfaces of the thermostat housing and engine.
   • Place the new thermostat in position, ensuring it sits correctly.
   • Install a new gasket or O-ring.
   • Reattach the thermostat housing and torque the bolts to manufacturer specifications (usually around 10-12 Nm).

3. Coolant Refill and Bleed

1. Reattach Hoses:

   • Reconnect any hoses that were disconnected during the process.

2. Refill Coolant:

   • Fill the cooling system with the appropriate type of coolant (check owner’s manual for specifications).

3. Bleed the System:

   • Start the engine with the radiator cap off to allow air to escape.
   • Monitor the coolant level and top off as necessary until no more air bubbles are present.

4. Reconnect Battery and Test

1. Reconnect Battery:

   • Reattach the negative battery terminal.

2. Clear Codes:

   • Use an OBD-II scanner to clear the P0128 code.

3. Test Drive:

   • Drive the vehicle to ensure the engine reaches the proper operating temperature and monitor for any return of the check engine light.