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

P0404

EGR Range/Performance

The EGR valve does not move through its expected range or its position feedback does not track command. The valve may be sticking, the position sensor may be drifting or carbon buildup is preventing full travel.

SystemPowertrain
Typegeneric / SAE
GroupP0
Range / number4 / 04

Possible causes

  • Carbon buildup on EGR valve high
  • Position sensor drift medium
  • Mechanical valve damage low

Symptoms

  • Check engine light on
  • Pinging or knocking under load
  • Power loss and hesitation
  • Possible rough idle
  • Failed emissions inspection (NOx)

Inspection / repair

  • Difficulty: medium
  • DIY: shop recommended
  • Estimated cost: 150–800 €
  • Estimated time: 0.5–3 h
  • Component: egr valve
  • Component: egr position sensor
  • 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