OBD-II reference

All 9.533 generic OBD-II codes, explained in detail.

Causes, inspection steps and sources — a comprehensive DIY archive. Created and maintained with love for the detail. Good luck and have fun!

Powertrain generic / SAE

P23A5

Exhaust Heat Exchanger Bypass Valve B Control Performance

The bypass flap A of the exhaust heat exchanger does not move as commanded - the position feedback or downstream temperature does not respond to the control demand. The flap is mechanically stuck, the actuator gearing is worn, or the position sensor is offset.

SystemPowertrain
Typegeneric / SAE
GroupP2
Range / number3 / A5

Possible causes

  • Flap stuck due to soot or carbon high

Inspection / repair

  • Difficulty: medium
  • DIY: shop recommended
  • Estimated cost: 250–1200 €
  • Estimated time: 1.5–4 h
  • Component: exhaust bypass valve b
  • MIL / check engine light
  • emissions-relevant

Sources

References

How to read OBD-II codes

The first letter names the vehicle system, the second digit distinguishes generic from manufacturer-specific, the remaining digits group fault area and number.

PPowertrain: engine, transmission, emissions
BBody: chassis trim, comfort, interior
CChassis: suspension, brakes, steering
UNetwork: CAN, control modules, communication