The dreaded P205B error code on your VW Passat often indicates a faulty AdBlue tank temperature sensor. This guide provides a DIY solution for addressing this specific sensor issue, bypassing the need for a costly tank replacement. This fix focuses solely on the temperature sensor malfunction and doesn’t address problems with the heaters or pump. If you experience other codes, especially during colder months, ensure the P205B code is the sole culprit after clearing all codes and restarting the engine.
Identifying the P205B Fault
Before proceeding, confirm that the P205B code is the only active error. Clear all existing codes using a diagnostic tool. Once the Check Engine Light (CEL) illuminates again, re-scan for codes. If only the P205B code returns, this fix is likely suitable for your situation. This code specifically points to a problem with the AdBlue tank temperature sensor, allowing you to confidently proceed with this targeted solution.
Sourcing the Replacement Sensor
The core component of this fix is a 10k ohm thermistor, readily available online for a few dollars. Ensure the thermistor is waterproof (H20 proof) for long-term reliability within the AdBlue tank environment. These are often marketed as aquarium tank temperature sensors, but double-check the resistance rating to guarantee it’s a 10k ohm variant. Choosing a high-quality, waterproof sensor ensures durability and accurate temperature readings.
Installing the New Sensor
Begin by removing the AdBlue tank. Locate the connector attached to the fill neck; this is where the new sensor will be connected. The small black and white wires on the bottom of this connector lead to the temperature sensor. Cut these wires on the sensor side, leaving enough length on the connector side for future repairs or replacements. This preserves the original connector for seamless integration if a complete tank replacement becomes necessary later. Seal the exposed wires from the old sensor to prevent corrosion or short circuits.
For this DIY fix, a hole was drilled into the fill cap to accommodate the new sensor. This is a cost-effective approach, as replacing the cap is significantly cheaper than the entire tank. Thread the new sensor wire through the drilled hole, ensuring sufficient length reaches the bottom of the tank for accurate temperature readings. Seal the hole thoroughly with silicone sealant to prevent leaks and ensure the integrity of the AdBlue system.
Alternative methods for inserting the sensor are possible, but consider future maintenance. A removable solution like the fill cap modification allows for easier access if the pump or heater requires replacement later.
Important Considerations
Using a new, high-quality thermistor is crucial for consistent performance. While a used sensor might work temporarily, it’s recommended to invest in a new component for reliability. This ensures accurate readings and avoids potential issues caused by a pre-owned sensor. This DIY fix addresses the P205B error code effectively, providing a cost-effective solution to a common VW Passat problem. Remember to handle the AdBlue tank and its components with care, as AdBlue is a corrosive substance.
