how to fix a P0128 code in 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 tools and parts.
• Ensure the vehicle is parked on a flat surface and the engine is cool.
• Disconnect the negative battery cable for safety.

2. Inspect and Replace the Coolant Temperature Sensor

• Tools Required:
  • Socket set
  • Torque wrench
  • Multimeter
• Sub-steps:
  1. Locate the coolant temperature sensor (usually near the thermostat housing).
  2. Disconnect the electrical connector from the sensor.
  3. Remove the sensor using the appropriate socket.
  4. Install the new coolant temperature sensor, tightening it to the manufacturer's specified torque.
  5. Reconnect the electrical connector.

3. Inspect and Replace the Thermostat

• Tools Required:
  • Socket set
  • Gasket scraper
• Sub-steps:
  1. Drain the engine coolant into a clean container.
  2. Locate the thermostat housing and remove the bolts using the socket set.
  3. Carefully remove the thermostat and gasket from the housing.
  4. Clean the mating surfaces to ensure a proper seal.
  5. Install the new thermostat and gasket, ensuring it is oriented correctly.
  6. Reinstall the thermostat housing and tighten the bolts to the manufacturer’s torque specifications.
  7. Refill the cooling system with the appropriate coolant.

4. Final Checks

1. Reconnect the negative battery cable.
2. Start the engine and let it warm up while monitoring the temperature gauge.
3. Check for any leaks around the thermostat housing and sensor.