AdBlue System Error: Defective Quality Sensor?

Dear forum community,

A friend's Audi A5 displayed an AdBlue error message on the instrument cluster, and the countdown timer until engine start prevention had begun.
The first fault was with heater 2 – specifically, according to my research, the transfer line from the tank to the injector, not the one inside the tank itself.
The cable was ordered, replaced, and the error could be cleared. Afterwards, I tried to reset the fill level in the MSG and also remove the lock, but this didn't work because a communication error occurred instead.
Fuses, wiring harness, and connectors visually inspected - no abnormalities found.

Does this indicate a faulty AdBlue control unit? Could the defective heater have damaged the control unit?

Thank you very much!

Best regards.
Alex.

Hello.

Quote:

66848 - Reduction agent quality module. U02A2 00 [00001101] - No communication. [SCR_Digital_Interface_2_Timeout] confirmed - checked since last deletion. Environmental conditions: Error priority: 2 Error frequency: 1. Lost Count: 51 Mileage: 163,391 km Date: 2026.01.02 Time: 17:37:40 Voltage at terminal 30A: 13.25 V. Voltage at terminal 30B: 13.25 V. Supply voltage for external components: 5.00 V. Donor for quality of the reducing agent: Voltage at terminal 31: 0.00 V. Pump for reducing agent: Speed: 0 rpm. Pump for reducing agent: Current: 0.00 A. Pump for reducing agent, operating status: slow pressure regulation. Pump for reducing agent: Control signal: 50.0%. Pump for reducing agent: Status - Active; Control - Enabled; Output Stage - Active. Pump for cooling agent: Final temperature: 5 °C. Heating circuit 1, for central control and dosing system: Final temperature: 1 °C. Donor for tank temperature reduction agent: Temperature: 1 °C. Pressure sensor for reducing agent: Voltage: 0.81 V. Level sensor for additive tank: Fill height: 232 mm. Reducing agent quality: Urea concentration: 107.0%. Donor 2 for temperature reduction: Current value: 82.00 °C. Heating circuit 1 for reducing agent: Power: 0 W. Heating circuit 1 for reducing agent: Setpoint power: 0 W. Heating circuit 1 for reducing agent: Power limit: 140 W. Heating circuit 3 for reducing agent: Power: 0 W. Heating circuit 3 for reducing agent: Setpoint power: 0 W. Heating circuit 3 for reducing agent: Power limit: 78 W. Heating circuit 2 for reducing agent dosing system: Power: 0 W. Heating circuit 2 for the reducing agent dosing system: Control: not active

Apart from the communication error, the environmental conditions seem to be good.

What do you mean by "resetting the level"? So, you pour AdBlue into the tank, preferably filling it completely. At least, in my case, the level indicator is rather inaccurate.

Based on the car scan, everything looks fine so far. Make sure the reducing agent pump is working (0 amps in the scan with 50% activation).

"Then, clear the error codes and, if a warning light is still illuminated on the instrument cluster, drive for 30 kilometers. The SCR system needs some time to update its status (at least in my T6)."


Best regards, Rainer.