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

P21A3

Cylinder 8 Air-Fuel Ratio Imbalance

Cylinder 8 fuel trim deviates significantly from the bank average — a single-cylinder injector or intake fault.

SystemPowertrain
Typegeneric / SAE
GroupP2
Range / number1 / A3

Possible causes

  • Injector clogged or leaking high

Inspection / repair

  • Difficulty: hard
  • DIY: shop recommended
  • Estimated cost: 200–2500 €
  • Estimated time: 1–6 h
  • Component: fuel injector
  • MIL / check engine light
  • emissions-relevant

Sources

References

sae:J2012

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