My VW Sharan displayed a low AdBlue warning alongside the engine warning light. The error code indicated insufficient reduction. After adding 10 liters of AdBlue and clearing the error, the remaining mileage indicator continued to countdown. Previously, a dealership needlessly installed an AdBlue heater. They then proposed replacing the entire exhaust system, catalytic converter, sensors, and high-pressure pump – essentially totaling the car. I halted the work.
The solution? Recalibrating the NOx sensor using VCDS. It took 15 minutes following the on-screen instructions. This points to a VW software error. My Sharan seems to drain the AdBlue tank, triggering the error. A flag is set, preventing a reset, even though the sensor recognizes a “Full” tank after refilling. The display could be reset by querying and utilizing this data, but it isn’t.
To reset the warning:
First, warm up the car and let it idle. Find a secluded spot, as the engine will run at an elevated idle for about 15 minutes.
Connect VCDS and access the engine control unit. Navigate to Basic Settings and initiate the SCR system test. The VCDS display will prompt you to press the gas and brake pedals simultaneously. The engine will rev to around 1300 RPM. After approximately 15 minutes, the test completes, confirming the system is okay. The AdBlue warning light will then disappear.
My condolences to those who had their entire SCR system replaced unnecessarily due to this software glitch. The dealerships, in their ignorance, likely stumbled upon the fix during the post-replacement system check. A costly and avoidable mistake. This highlights the value of VCDS remaining applications for diagnosing and resolving such issues. By using VCDS, costly and unnecessary repairs can often be avoided.
