Powertrain, generic · Auxiliary emission controls

P04A6 Exhaust Pressure Control Valve B Position Sensor/Switch Circuit

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. P04A6 is the general circuit fault or open circuit of valve B's position sensor. Bentley reports bank 2 sensor faults as P04A8 instead. No manufacturer document available to us uses this code; the description mirrors the valve A counterpart P048B and CARB's monitoring requirement for input and output components.

Likely causes

Actuator with integrated position sensor faulty
Connector or wire at the underbody corroded, chafed or open
Engine module (sensor supply or input)

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€100–900
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

P04A7P04A8P04A9P04AAP048B

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