P204A: reductant pressure feedback below 0.1 V is an electrical finding

P204A describes the reductant pressure-sensor circuit. Audi's CPNB diagnostic row is more specific: an open circuit or short to ground, with signal voltage below 0.1 V. The monitor therefore evaluates electrical feedback rather than directly specifying a measured fluid-pressure deficit.

Low voltage is not zero pressure

As diagnostic interpretation, an unreliable pressure signal cannot be treated as a calibrated statement that the reductant system has no pressure. The row supplies no voltage-to-pressure conversion and no pump-output requirement. Those values must come from the actual sensor and system information.

The combined open-or-grounded description also leaves more than one electrical explanation. A single code does not locate the defect or prove that the pressure sensor itself is internally damaged.

Establish signal credibility before judging delivery

The useful next evidence explains the low sensor signal using the CPNB wiring procedure, then supports whatever hydraulic assessment is appropriate. This is an interpretation of the distinction between signal and measured quantity, not an OEM repair sequence reproduced from the chart. The 2014 Audi A6/S6 reference gives no universal connector pinout or instruction to replace the dosing pump solely because P204A was stored.

Source: Audi 2014 A6/S6 Quick Reference Specification Book.