Powertrain, generic (extended)

P28DD Clutch B Pressure Sensor Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

Set when the voltage from the clutch B pressure sensor falls below the lowest value the part can produce in normal service. Usually the signal line has a short to ground, the sensor supply is missing or the sensor has failed internally. Because the reading lies outside the valid band, the module treats it as an electrical fault rather than as low pressure. No manufacturer documents P28DD publicly. Patents from Getrag and Audi place one pressure sensor at every clutch of a twin-clutch gearbox so the controller can regulate clutch pressure directly; under CARB rules such inputs need an out-of-range check. P28DE is the high counterpart, P28DC the open circuit and P28CE the same fault on clutch A. Shifts that need clutch B may be blocked.

Likely causes

Sensor signal wire chafed through and shorted to ground
Sensor supply voltage missing or pulled down by another shorted sensor on the same supply
Pressure sensor electronics failed

Symptoms

  • Transmission warning or check engine light on
  • Transmission in emergency mode, some gears unavailable
  • Harsh or delayed engagement

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–1,800
Time0.5–5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

clutch pressure sensor bwiring harnesstcm

Related codes

P28DCP28DEP28DFP28CE

References: law.cornell.edu, patents.google.com, patents.google.com.