Powertrain, generic · Auxiliary emission controls

P04A9 Exhaust Pressure Control Valve B Position Sensor/Switch Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

An exhaust pressure control valve is an electrically driven flap in the exhaust with a position sensor or end-position switch, usually inside the actuator. Valve B is the second such flap; Bentley's V8 assigns A to bank 1 and B to bank 2. Documented uses are the flap behind the particulate filter of VW's and Audi's 2.0 TDI, which raises back pressure for the low-pressure EGR, and the sound flaps of Audi and Bentley. P04A9 means valve B's position signal is above its window – open signal or short to positive. No manufacturer document available to us uses this code; the description mirrors the valve A counterpart P048E and CARB's monitoring requirement for input and output components.

Likely causes

Actuator electronics (position sensor) faulty
Signal or ground wire open
Connector corroded
Signal shorted to positive

Symptoms

  • Check engine light on
  • Flap without function, exhaust sound changed
  • VW/Audi TDI: EGR fault P0401 possible

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€100–700
Time0.5–2.5 h

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

Parts involved

exhaust pressure control valve b position sensorexhaust pressure control valve bsensor wiringengine control module

Related codes

P04A6P04A8P04A7P04AAP048E

References: law.cornell.edu, static.nhtsa.gov.