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

P234D

Cylinder 9 Pressure Too Low

Cylinder 9 measured peak combustion pressure is below the calibrated minimum — typically low compression, weak injection, or stuck-open exhaust valve.

SystemPowertrain
Typegeneric / SAE
GroupP2
Range / number3 / 4D

Possible causes

  • Low compression on cylinder 9 (valves, rings, head gasket) high
  • Injector flow too low medium

Inspection / repair

  • Difficulty: hard
  • DIY: shop recommended
  • Estimated cost: 400–3500 €
  • Estimated time: 2–10 h
  • Component: cylinder 9 combustion
  • Component: cylinder compression
  • Component: fuel injector cyl 9
  • 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