Powertrain, generic · Auxiliary emission controls

P04A2 Exhaust Pressure Control Valve B 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. P04A2 means valve B's control circuit is high, i.e. shorted to positive; VW documents the valve A counterpart P0478 on the 2015 2.0 TDI, where the actuator is replaced. No manufacturer document available to us uses this code; the description mirrors the valve A counterpart P0478 and CARB's monitoring requirement for input and output components.

Likely causes

Control wire shorted to positive
Actuator electronics faulty
Connector corroded or wet

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€100–800
Time0.5–2.5 h

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

Parts involved

exhaust pressure control valve bvalve actuatoractuator wiringengine control module

Related codes

P049FP04A1P04A3P0478

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