DTC P12A2: Fuel High-Pressure Sensor Implausible: Explanation

The inlet for the fuel high-pressure rail behind the high-pressure pump is blocked either fully or partially by foreign bodies.

OR 

The connection between the two fuel high-pressure rails is blocked either fully or partially by foreign bodies.

The inlet of the respective rail is constricted by a restrictor, which is used to dampen pressure peaks.

• The fuel high-pressure sensor, which is fitted at the end of the lines, measures a pressure increase that is too slow, or a rapid drop in pressure when the fuel injectors open.
• As a result, fuel high-pressure that is too high is set in the rail AHEAD OF the blockage, while at the same time, there is insufficient pressure and volume BEHIND the blockage.
• The oxygen sensors of the affected bank measure a large oxygen surplus, while at the same time, fuel trim adaptation tries to enrich the mixture as much as possible (extension of the injection time).